Citation
Using stable carbon ssotope, microwear, and mesowear analyses to determine the paleodiets of neogene ungulates and the presence of C4 or C3 grasses in Northern and Central Florida

Material Information

Title:
Using stable carbon ssotope, microwear, and mesowear analyses to determine the paleodiets of neogene ungulates and the presence of C4 or C3 grasses in Northern and Central Florida
Creator:
Hoffman, Jonathan M. ( Dissertant )
Bloch, Jonathan I. ( Thesis advisor )
Hodell, David ( Reviewer )
Hulbert, Richard ( Reviewer )
Zimmerman, Andrew ( Reviewer )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
2006
Language:
English
Physical Description:
x, 102 p.

Subjects

Subjects / Keywords:
Fauna ( jstor )
Fossils ( jstor )
Grasses ( jstor )
Isotopes ( jstor )
Mammals ( jstor )
Specimens ( jstor )
Taxa ( jstor )
Teeth ( jstor )
Tooth enamel ( jstor )
Ungulates ( jstor )
Geology thesis, M.S ( local )
Dissertations, Academic -- UF -- Geological Sciences ( local )
Greater Orlando ( local )

Notes

Abstract:
Traditionally, hypsodont (high-crowned) teeth in North American ungulates (hoofed mammals) were thought to have coevolved with grasses during the middle Miocene. Isotopic evidence has demonstrated that tropical Câ‚„ grasses were not dominant and therefore not abundant enough to be responsible for this adaptive radiation. It has been proposed that high-altitude C₃ grasses were extensive throughout the Great Plains and were the dietary driving force behind the grazing adaptations. This study will test this hypothesis to see if it applies to the middle Miocene of the Southeastern United States. The [lower case delta]¹³C values from 24 specimens of 8 ungulate taxa from the Willacoochee Creek Fauna, an assemblage of middle Miocene mammals from northern Florida and southern Georgia, are presented here to determine if there is a significant Câ‚„ grass component in mammalian paleodiets. The [lower case delta]¹³C values indicate that all 8 taxa were consuming C₃ plant material, either browse or grass. Furthermore, microwear analyses conducted on 3 specimens of the most hypsodont taxon indicate that the mammal was eating grass. Combined with the [lower case delta]¹³C data, this study concludes that C₃ grasses were present in the middle Miocene of northern Florida and at least one hypsodont mammal was consuming them. This evidence supports a C₃ grass hypothesis of hypsodont radiations. Also, this study combines the mesowear paleodietary analysis with previously published isotopic data to 5 equid populations from 3 sites in central Florida, ranging in age from ~9.5 Ma to ~1.5 Ma, to trace the possible influence of C₃ grasses on ungulate diets. C₃ grasses were the primary food source for these horses until approximately 7 Ma. After that, the horses fed on a mixed diet of C₃ and Câ‚„ grasses until about 1.5 Ma. At that point in Florida, the abundance of C₃ grasses had diminished and the grazers primarily fed on Câ‚„ grasses.
Subject:
C₃, C₄, carbon, grass, grazing, Isotopes, Miocene, Paleoecology, Pliocene
General Note:
Title from title page of source document.
General Note:
Document formatted into pages; contains 112 pages.
General Note:
Includes vita.
Thesis:
Thesis (M.S.)--University of Florida, 2006.
Bibliography:
Includes bibliographical references.
General Note:
Text (Electronic thesis) in PDF format.

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University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Hoffman, Jonathan M.. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
3/1/2007

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USING STABLE CARBON ISOTOPE, MICROWEAR, AND MESOWEAR
ANALYSES TO DETERMINE THE PALEODIETS OF NEOGENE UNGULATES
AND THE PRESENCE OF C4 OR C3 GRASSES IN NORTHERN AND CENTRAL
FLORIDA













By

JONATHAN M. HOFFMAN


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2006

































Copyright 2006

by

Jonathan M. Hoffman
















ACKNOWLEDGMENTS

I would like to thank my advisor, Dr. Jonathan Bloch for his guidance on this

proj ect. I would also like to thank my committee members: Dr. David Hodell, Dr.

Richard Hulbert, and Dr. Andrew Zimmerman. Their suggestions and advice are greatly

appreciated. In addition to their helpful advice, Dr. Bloch, Dr. Hulbert, and Dr.

Zimmerman all aided in collecting fossil samples. I would like to thank Art Poyer and

Jeremy Green for their help in collecting samples. I am especially appreciative of the

Englehard Corporation and Dave Mihalik for allowing me to collect fossils from their

mines and being incredibly helpful at those sites.

I would like to thank Dr. Penny Higgins for her assistance in learning the

sampling techniques for stable isotope analysis of fossil teeth and the chemical protocol

for preparing those samples for analysis. I am greatly indebted to Dr. Jason Curtis for

running my samples on the mass spectrometer and for all of his advice.

My fellow graduate students aided me with discussion and advice. I am very

appreciative of P.J. Moore, Warren Grice, Jane Gustayson, and Derrick Newkirk for

listening and providing support. Finally, I would like to thank my family, who has always

supported me and encouraged me to pursue my passions.




















TABLE OF CONTENTS


page

ACKNOWLEDGMENT S ............. ...... .............. iii...


LIST OF TABLES ............. ...... ..............vi...


LI ST OF FIGURE S .............. .................... vii


AB STRAC T ................ .............. ix


CHAPTER


1 INTRODUCTION ................. ...............1.......... ......


2 FIELD AREA AND FAUNA ................. ...............17........... ...


3 MESOWEAR METHOD .............. ...............29....


Material s and Method s .............. ...............3 1....
Re sults............. ...... ._ ...............32...


4 MICROWEAR METHOD .............. ...............40....


Materials and Methods .............. ...............41....
Re sults............. ...... ._ ...............44...


5 STABLE ISOTOPE ANALYSIS .............. ...............48....


Back ground ............. ...... ._ ...............48...
Materials and Methods .............. ...............54....
Re sults............. ...... ._ ...............57...


6 DI SCUS SSION ............. ...... .__ ...............67..


7 CONCLUSIONS .............. ...............80....


APPENDIX


A MESOWEAR VALUES LISTED BY SAMPLE................ ...............82


B SERIAL STABLE ISOTOPE VALUES .............. ...............86....





1V





















LIST OF REFERENCES ................. ...............88................


BIOGRAPHICAL SKETCH ................. ...............102......... ......



































































v

















LIST OF TABLES


Table pg

2-1 Biochronological ranges of the Willacoochee Creek Fauna. ............. ........._......23

3-1 Systematic and morphological information about the taxa used in the mesowear
analy si s. .............. ...............3 5....

3-2 Observed percentages of mesowear attributes (% high and % low refer to the
percentage of specimens with high or low occlusal relief and % sharp, % round,
and % blunt refer to the percentage of specimens with sharp, round or blunt cusp
shape). ............. ...............36.....

3-3 Dietary classifications based on hierarchical cluster analyses of mesowear
attributes from Table 3-2 ................. ...............36........... ...

4-1 Individual microwear counts for 3 specimens ofAcritohippus isonesus and 7
specimens of Neohipparion trampa~sense. ............. ...............46.....

4-2 Calculated average microwear values and percentages for Acritohippus isonesus
and Neohipparion trampasense.............. ...............4

4-3 Isotopic data for equids from 4 central Florida sites. ............... ...................4

5-1 List of the 24 specimens analyzed for stable carbon and oxygen isotope analysis..60

5-2 Bulk stable carbon and oxygen isotope values for Willacoochee Creek Fauna.......61

5-3 Descriptive statistics of the 613C and 68 values for 8 herbivores from the
Willacoochee Creek Fauna. ........... ....._.._ ...............62...

6-1 Isotopic data for equids from 4 central Florida sites. ............... ...................7

A-1 Abbreviations: UF ID = catalogue number in Florida Museum of Natural
History collections,............... ..............8

B-1 Abbreviations: ELC = Englehard La Camelia Mine, MGF = Milwhite Gunn
Farm Mine, and LC2 = La Camelia 2 Mine. .............. ...............86....

















LIST OF FIGURES


Figure pg

2-1 Index map of middle Miocene localities in northern Florida. ........._._... ........._.....22

2-2 Composite section of the Torreya Formation and the location of the
Willacoochee Creek Fauna within the Dogtown Member. .............. ...................24

2-3 Correlated stratigraphic sections of the Englehard La Camelia and Milwhite
Gunn Farm Mines............... ...............25.

2-4 Fresh cut at the newest site, the Crescent Lake Mine, in Decatur County,
G eor gia. .............. ...............26....

2-5 Stratigraphic and temporal distribution of the 3 fossil sites studied in the
mesowear analysis, as well as a fourth (Moss Acres) ................ ..........__........27

2-6 Tooth positions. .............. ...............28....

3-1 Dendrogram illustrating the hierarchical cluster analysis of the 27 'typical'
grazers, browsers, and mixed feeders from Fortelius and Solounias (2000). ..........34

3-2 Examples of typical mesowear attributes ................. ...............35...............

3-3 Dendrograms illustrating the hierarchical cluster analyses of 6 studied taxa
amongst the 27 'typical' grazers, browsers, and mixed feeders from Fortelius
and Solounias (2000)............... ...............37.

5-1 Schematic of isotopic fractionation between atmospheric carbon and C3 plants,
as well as fractionation between C3 plants and ruminant herbivores. ......................59

5-2 Plot of bulk 813C VS. 6180 values for the 8 herbivores from the Willacoochee
Creek Fauna. ........... ..... ..._. ...............63.....

5-3 613C ValUeS for serial samples of two Aphelops specimens. ................ ................64

5-4 6 O0 values for serial samples of two Aphelops specimens. ................ ................64

5-5 613C ValUeS for serial samples of two M~erychippus primus specimens. ................65

5-6 6 O0 values for serial samples of two M~erychippus primus specimens. ................65










5-7 613C ValUeS for serial samples of two Acriohippus isonesus specimens. .................66

5-8 68 O values for serial sampling of two Acritohippus isonesus specimens. ..............66

6-1 Plot of microwear index versus 613C ValUeS. ................ ............... .............78















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

USING STABLE CARBON ISOTOPE, MICROWEAR, AND MESOWEAR
ANALYSES TO DETERMINE THE PALEODIETS OF NEOGENE UNGULATES
AND THE PRESENCE OF C4 OR C3 GRASSES IN NORTHERN AND CENTRAL
FLORIDA

By

Jonathan M. Hoffman

December 2006

Chair: Jonathan I. Bloch
Major Department: Geology

Traditionally, hypsodont (high-crowned) teeth in North American ungulates

(hoofed mammals) were thought to have coevolved with grasses during the middle

Miocene. Isotopic evidence has demonstrated that tropical C4 graSses were not dominant

and therefore not abundant enough to be responsible for this adaptive radiation. It has

been proposed that high-altitude C3 graSses were extensive throughout the Great Plains

and were the dietary driving force behind the grazing adaptations. This study will test

this hypothesis to see if it applies to the middle Miocene of the Southeastern United

States. The 613C ValUeS from 24 specimens of 8 ungulate taxa from the Willacoochee

Creek Fauna, an assemblage of middle Miocene mammals from northern Florida and

southern Georgia, are presented here to determine if there is a significant C4 graSS

component in mammalian paleodiets. The 613C ValUeS indicate that all 8 taxa were

consuming C3 plant material, either browse or grass. Furthermore, microwear analyses









conducted on 3 specimens of the most hypsodont taxon indicate that the mammal was

eating grass. Combined with the 613C data, this study concludes that C3 graSSCS WeTO

present in the middle Miocene of northern Florida and at least one hypsodont mammal

was consuming them. This evidence supports a C3 graSs hypothesis of hypsodont

radiations. Also, this study combines the mesowear paleodietary analysis with previously

published isotopic data to 5 equid populations from 3 sites in central Florida, ranging in

age from ~9.5 Ma to ~1.5 Ma, to trace the possible influence of C3 graSses on ungulate

diets. C3 graSses were the primary food source for these horses until approximately 7

Ma. After that, the horses fed on a mixed diet of C3 and C4 graSses until about 1.5 Ma. At

that point in Florida, the abundance of C3 graSses had diminished and the grazers

primarily fed on C4 graSSCS.















CHAPTER 1
INTTRODUCTION

Today, over 25% of North American natural biomes are nonforest (Webb, 1977).

The modern vegetation of North America is a sharp contrast to vegetation at the

beginning of the Cenozoic, when nearly all of North America was covered with forests

(Webb, 1977). Traditionally, paleontologists have believed that, beginning in the

Paleocene, parts of North America underwent a stepwise progression from forest to

savanna to grassland biomes (Webb, 1977). For most of the Paleocene, North America

was dominated by evergreen forests and cypress swamps (Wolfe, 1985; Wing and

Tiffney, 1987). It has been proposed that grasses originated amongst this vegetation in

the early Paleocene, although no direct evidence of grasses has been found in sediments

of that age (Linder, 1986; Crepet and Feldman, 1991). Nearly all the mammals in the

Paleocene belong to four orders: the Multiuberculata, Insectivora, Primates, and

'Condylarthra' (Webb and Opdyke, 1995). These mammals were small to medium in size

and were arboreal or scansorial (Webb and Opdyke, 1995). The multituberculate

Ptilodus, for example, possesses morphological adaptations consistent with those of a

modern tree squirrel, suggestive of an arboreal habit (Jenkins and Krause, 1983).

The grassland transitional sequence began meekly, during the late Paleocene with

the appearance of possible protosavannas in scattered open-country areas that constitute

breaks in the forest coverage (Webb, 1977). In the late Paleocene Crazy Mountain Field

of Montana, Simpson (1937) found that 90% of the fossils collected from floodplain

sediments consisted of carnivores and archaic ungulates such as perptychids,










phenacodontids, and arctocyonids. In the same area, taxa collected from swampy

woodland deposits were typically smaller, arboreal mammals (Simpson, 1937). A similar

pattern is apparent in late Paleocene and early Eocene sediments of the Rocky Mountain

intermontane basins. The late Paleocene Fort Union Formation from that region consists

of gray sediments indicative of swampy woodlands bounded by alluvial plains (Van

Houten, 1945; Bown, 1980). Small arboreal mammals have been collected from these

sediments, corroborating the environmental interpretation of woodlands (Van Houten,

1945). The early Eocene Willwood Formation, located in the same area, exhibits red-

banded flood plain sediments and ungulates suited for open-country habitation (Van

Houten, 1945; Bown, 1980; Hickey, 1980; Wing, 1980). Van Houten (1945) concluded

that the late Paleocene Rocky Mountain woodlands had, by the early Eocene, developed

flood plain savannas that existed in breaks in the forest.

A number of subtle modifications are evident in probable open-country taxa during

the late Paleocene and early Eocene. The condylarth M~eniscotherium exhibits molarized

premolars, molar crescents, and some cursorial limb elongation (Gazin, 1965), attributes

that improved the mastication of coarser vegetation and open-country locomotion. In the

Torrej onian North American Land Mammal Age (NALMA) of the middle Paleocene,

three orders of larger Asian immigrants arrived in North America: the Pantodonta,

Taeniodonta, and Dinocerata (Webb and Opdyke, 1995). Titanoides, a late Paleocene

pantodont, bears digging forelimbs that would have excavated coarse roots (Webb, 1977).

Taeniodonts, large clawed opossum-like root grabbers, were the first mammals to

develop hypsodont (high-crowned) teeth (Patterson, 1949). Crested molars and molarized

premolars are also seen at this time in the uintatheres (Order Dinocerata), which bear









"hornlike protuberances" indicative of herding behavior seen in open-country ungulates

(Wheeler, 1961).

Global climate fluctuated during the Paleocene. Deciduous tree populations began

increasing at about 63 Ma, indicative of cooling climate (Rose, 1981). This cooling trend

began near the boundary of the Torrej onian and Tiffanian and continued through the

Tiffanian, accompanied by the disappearance of small mammals and an increased

presence of larger mammals (Webb and Opdyke, 1995). The Tiffanian cooling trend was

followed by the initial appearance of open-country habitats that coincides with a global

warming trend at the end of the Tiffanian (Koch, Zachos, and Gingerich, 1992). This

warming trend began in the middle Paleocene (about 59 Ma) and peaked and ended with

the early Eocene Climatic Optimum (EECO, 52-50 Ma) (Zachos, Pagani, Sloan, Thomas,

and Billups, 2001). At northern latitudes, the peak mean annual temperature in the early

Eocene was between 250C and 300C, 150C to 200C warmer than today (Novacek, 1999).

The warming trend and EECO are marked by a 1.5%o decrease in 68 O values from

benthic foraminifera, the lowest such 68 O values in the Cenozoic (Zachos et al., 2001).

This global warmth had a maj or impact on both North American floral and faunal

communities. Between 55 and 53 Ma, the number of macrofloral species doubled in the

Paleocene/Eocene of the Bighorn Basin (Wing, Alroy, and Hickey, 1995). Early Eocene

fossil leaves exhibit "drip-tips" and smooth margins indicative of a tropical/subtropical

climate (Wolfe, 1978; Prothero, 1994). The evergreen forests of the Paleocene had given

way to early Eocene subtropical forests, while still maintaining some open-country

enclaves (MacGinitie, 1974; Rose, 1981; Bown and Krause, 1981, 1987).









The beginning of the Clarkforkian (latest Paleocene), at about 56 Ma, is marked by

the first maj or immigration episode of Asian mammals capable of exploiting the new

North American open-country niches (Webb and Opdyke, 1995; Lofgren, Lillegraven,

Clemens, Gingerich, and Williamson, 2004). The newly arrived Asian orders included

the Tillodontia and Rodentia, as well as the pantodont family Coryphodontidae (Rose,

1981; Krause and Maas, 1990). Many of these mammals had adapted to grazing lifestyles

in Asia. For example, Coryphodon, one of the Asian pantodonts that arrived in North

America in the late Paleocene, is believed to have already been a hippo-like amphibious

grazer that, based on canine grooves, rooted for food (Simons, 1960). In all, nine genera

immigrated from Asia to North America in the Clarkforkian (Stucky, 1990).

The Clarkforkian immigration episode continued into the Wasatchian, in the

earliest Eocene (Webb and Opdyke, 1995). The Clarkforkian-Wasatchian boundary

correlates with the Paleocene-Eocene boundary at about 55 Ma (Gingerich, 2001). The

early Wasatchian was subj ect to the largest mammal immigration wave in the North

American fossil record. At this time, European mammals crossed the North Atlantic over

the Thulean land bridge (Webb and Opdyke, 1995). This immigration episode included

the first North American appearances of order Perissodactyla (Hyracotherium), order

Artiodactyla (Diacodexis), the creodont family Hyaenodontidae, and the primate families

Adapidae and Omomyidae (Rose, 1981). Direct evidence of grass during the late

Paleocene and early Eocene is rare, but there are some fossil grasses that indicate the

presence of protosavannas: the oldest North American grass macrofossil, early Eocene in

age, comes from the Paleocene/ Eocene Wilcox Formation of western Tennessee (Crepet

and Feldman, 1991).









The morphological subtleties visible during the late Paleocene/early Eocene gave

way, in the middle and late Eocene, to more pronounced adaptations and shifts in both

floral and faunal communities due to the changing global climate. In the middle Eocene,

the global climate began cooling again and becoming drier, as evident from a 3.0%o

increase in benthic foraminifera 618O values over a 17 million year span, from 50 Ma to

33 Ma (Savin, 1977; Zachos et al., 2001). The increase in 618O values in the middle

Eocene (50-48 Ma) resulted entirely from a decrease in deep-sea temperature from about

120C to about 4.50C (Zachos et al., 2001). Subsequent ice sheet growth began by the late

Eocene (34 Ma) and was responsible for further 618O enrichment (Miller and Katz, 1987;

Zachos, Stott, and Lohmann, 1994; Zachos et al., 2001). It was also during the middle

Eocene that the first signs of seasonal aridity, such as evaporites and oxidized redbeds,

appear in the Rocky Mountain region (Webb and Opdyke, 1995).

As aridity and cooling increased in the middle Eocene, there was a maj or faunal

turnover in the subtropical forests. By the end of the Duchesnean, 80% of the terrestrial

mammal genera present in the Uintan (the previous age) had become extinct (Savage and

Russell, 1983; Stucky, 1990). The gradual disappearance of tropical forests in North

America prompted the decline of arboreal creatures such as primates (Webb, 1977). The

adapids and paromoyids, the last of the North American primates, disappeared at the end

of the Duchesnean (Prothero, 1994). The orders Condylarthra, Tillodontia, Dinocerata,

and Taeniodonta also disappeared in the late Duchesnean (~40 Ma), while many new

Asian immigrants arrived, most notably the eubrontotheres such as Duchesneodus

(Webb, 1977; Emry, 1981; Krishtalka et al., 1987; Prothero, 1994).










By the late Eocene, the cooler and drier climate allowed for the first true savannas

to dominate the midcontinent (Webb, 1977; Wing and Tiffney, 1987). Savannas, as

defined by Sears (1969), are any biomes that are subtropical open-country plains with

some trees, which includes areas such as thorn scrub and open deciduous forests, but do

not include open steppe or grasslands. The savannas that appeared in the late Eocene

were savanna woodlands, typified by the presence of the Leguminosae, Sapindaceae, and

Anacardiaceae floral families, similar to those of the modern Chihuahua region of

Mexico (Webb, 1977). As the global cooling continued, tropical flora and subtropical

forests retreated south of the Rocky Mountains (Leopold and MacGinitie, 1972).

Members of the grass family Poaceae are also present in the late Eocene.

Representatives of the subfamily Pooideae, from Tribes Stipeae ("e.g.", Stipa florissanti)

and Phalarideae, appear in the Florissant floral assemblage of Colorado, at about 34 Ma

(MacGinitie, 1953; Stebbins, 1981). The presence of these two tribes, endmembers of

two separate evolutionary lineages, suggests that the Pooideae was well-differentiated by

the end of the Eocene (Stebbins, 1981).

The new savanna woodland habitats were exploited by a number of adapting North

American mammals, as well as by late Eocene Asian immigrants already adapted to

savanna habitats. The combined autochthounous and invasive taxa, which followed the

Duchesnean faunal turnover, are termed the "White River chronofauna" (Emry, 1981).

Chronofaunas are assemblages of species that remain compositionally stable over a

significant amount of time (Olson, 1952). The "White River chronofauna" consists of an

increase in herbivore genera and species from the late Eocene through the Oligocene,

beginning around 40 Ma (Krishtalka et al., 1987; Webb and Opdyke, 1995). The number









of identified browsing mammalian genera rose from 8 in the Duchesnean to about 40

after the Duchesnean (Stucky, 1990). Likewise, the overall number of mammalian

herbivore species rose from less than 40 to about 90 during the Eocene-Oligocene

transition (Savage and Russell, 1983). The higher species numbers were maintained

throughout the Oligocene (Webb, 1989). Numerous modern mammalian families make

their first appearance in North America during the late Eocene, including: soricid

insectivores; sciurid, castorid, cricetid, and heteromyid rodents; leporid lagomorphs;

canid and mustelid carnivores; camlids; tyassuids; and rhinocerotids (Webb and Opdyke,

1995).

By the middle Oligocene, the "White River chronofauna" had become the first

North American chronofauna to exhibit significant diversity of hypsodont herbivores,

from rodents to ungulates (Gregory, 1971; Webb and Opdyke, 1995). These hypsodont

taxa include: leporids, castorids, comyids, rhinocerotids, hypertragulids, oromerycids,

and oreodonts (Webb, 1977). The oromerycid M~ontanatylopus, for example, has molars

significantly more hypsodont than its brachydont sister taxa (Prothero, 1986). The newest

Asian taxa, introduced through the connection of the North American and Asian

continents (McKenna, 1972), included a suite of selenodont (crescent-toothed)

artiodactyls already adapted for savanna feeding (Webb, 1977). Included in this group are

the families Camelidae, Hypertragulidae, Leptomerycidae, and Agriochoeridae (Webb,

1977). The newly introduced taxa flourished in the fresh savanna environments. One

taxon native to North America, Hyopsodus, acquired more lophodont (crest-toothed)

molars to chew coarser food (Gazin, 1968). Native rodents, such as the protoptychids and

cylindrodontids, developed open-country locomotive adaptations as well as dentitions









suited for coarser foods (Wood, 1962; Black and Dawson, 1966; Galbreath, 1969;

Wahlert, 1973). Larger herbivores existed in two general groups: semiamphibious

streamdwellers such as amynodont rhinos and long-limbed, cursorial taxa that roamed the

interfluves, such as equids (M~esohippus) and selenodont artiodactyls (Wall, 1982).

These adaptations, along with the diversification of many of these cursorial and

hypsodont taxa, mark the dominance of the woodland savannas that had become

widespread in the Oligocene (Webb, 1977). It is also likely that the "White River

chronofauna" established a positive feedback loop with the savanna biomes:

Large herbivores preferred feeding in more open woodlands; in turn, expansion of
open formations facilitated evolution of mixed-feeding herbivores. (p., 192, Webb
and Opdyke, 1995)

Additionally, there was a negative correlation between browsers and the spread of open-

country habitats (Webb and Opdyke, 1995). By the late Oligocene, browsers such as

titanotheres had disappeared as woodland savannas continued to spread (Webb and

Opdyke, 1995).

The expansion of woodland savannas is supported not only by hypsodont radiations

but other lines of both floral and faunal evidence. Aquatic reptiles in the Rocky Mountain

area underwent severe population decreases as a result of aridity and seasonality during

the late Eocene and Oligocene (Hutchinson, 1982). The late Eocene Florissant Flora of

Colorado records a decrease in the percentage of entire-margined leaves, indicating a

drop in mean annual temperature from 100C to ~12.50C (MacGinitie, 1962; Wolfe,

1985). Additionally, pedological studies on the Brule Formation of South Dakota (~33

Ma, early Orellan) and the Upper John Day Formation in central Oregon (~30 Ma,









earliest Arikareenan) suggest the presence of desert bunch grasslands during the

early/middle Oligocene (Retallack, 1997; Retallack, 2001; Retallack, 2004).

Grass, however, was still relatively rare in the fossil record of the Eocene and

Oligocene (Frederickson, 1981; Webb and Opdyke, 1995; Jacobs, Kingston, and Jacobs,

1999). There are two plausible explanations for this rarity. The first is that woody shrubs

dominated the landscape prior to the profusion of grasses (Huber, 1982). The second

possibility is that grasses suffer from a taphonomic bias, preventing the preservation of

grasses despite their actual abundance (Webb and Opdyke, 1995). Grasses are known to

be abundant elsewhere during the middle Eocene, including Australia (Truswell and

Harris, 1982) and Europe (Litke, 1968).

Immediately following the Eocene-Oligocene transition, the Drake and Tasmania

Passages opened (at ~31 and 32 Ma, respectively), increasing ocean circulation and

proliferating the global cooling trend from the Eocene (Lawyer and Gahagan, 2003). This

also allowed the establishment and preservation of permanent Antarctic ice sheets

(Hambrey, Ehrmann, and Larsen, 1991). The decrease in global temperature continued

until the late Oligocene (26 to 27 Ma), when another warming trend began (Miller,

Wright, and Fairbanks, 1991; Wright, Miller, and Fairbanks, 1992). This warming trend

reduced Antarctic ice sheet volume until the middle Miocene, ~15 Ma (Miller et al.,

1991; Wright et al., 1992). There were some short glaciation events interspersed

throughout this approximately 12 million year interval (Wright and Miller, 1993). This

warming reached its zenith during the middle Miocene Climatic Optimum (MCO), from

17-15 Ma, which is evident from decreased 68"O values (Vincent, Killingley, and Berger,

1985; Flower and Kennett, 1995). Oceanic and atmospheric cooling and ice sheet growth









followed the MCO, marked by about a 1%o increase in foraminifera 618O values from

14.0 to 13.8 Ma (Flower and Kennett, 1995).

There are two hypotheses for the mechanism that drove the middle Miocene

climate variability: greenhouse gases and oceanic circulation (Zachos et al., 1994). From

16.5 to 13.5 Ma, overlapping the MCO, benthic foraminifera 613C ValUeS WeTO eleVated

as high as 2.2%o (Vincent and Berger, 1985). This event, termed the Monterey Excursion,

possibly resulted from the draw down of atmospheric pCO2 through organic carbon

burial in marginal marine sediments (Vincent and Berger, 1985). It has been proposed

that the Monterey Excursion drove middle Miocene climate variability, although there is

a 2.5 million year lag between the onset of the proposed pCO2 draw down (16.5 Ma) and

the atmospheric cooling indicated by the 618O increase at 14 Ma (Vincent and Berger,

1985; Hodell and Woodruff, 1994). Atmospheric CO2 leVOIS and global climate may have

remained high during this lag due to the outgassing of CO2 fTOm the Columbia River

Flood Basalt from 17 to 14.5 Ma (Hodell and Woodruff, 1994). However, other

researchers have suggested that atmospheric CO2 leVOIS were low from 17 Ma to 14 Ma

(Pagani, Freeman, and Arthur, 1999; Flower, 1999; Royer et al., 2001). The middle

Miocene climate variability, therefore, may have resulted from the opening and closing of

tectonic gateways that altered oceanic circulation (Woodruff and Savin, 1989, 1991;

Raymo, 1994).

The first immigration episode of the Miocene occurred at approximately the same

time as the beginning of the MCO, from 18-17 Ma in the middle Hemingfordian (Webb

and Opdyke, 1995). These Asian immigrants include comyid rodents, the

biostratigraphically important cricetid rodent Copemys, and the first true cats in the New









World such as Pseudaeherus (Webb and Opdyke, 1995). The immigration also included

four "megaherbivores": the rhinocerotids Teleocera~s and Aphelops and the proboscideans

M~ioma~stodon and Gomphotherium (Webb and Opdyke, 1995). It is assumed that these

"megaherbivores" modified the savanna landscape much like modern elephants,

however, there is no direct evidence to support this hypothesis (Owen-Smith, 1988).

These immigrants comprise part of the "Sheep Creek chronofauna" of the early and

middle Miocene. The "Sheep Creek chronofauna" is also important because it chronicles

the grazing advancement of horses, with the transition of the browsing/mixed feeding

Parahippus to the grazing M~erychippus (Hulbert and MacFadden, 1991).

Treeless grassland prairies were initially thought to have become widespread in the

Great Plains at the beginning of the Barstovian Land Mammal Age (middle Miocene,

~15.8 Ma), replacing the steppe savannas (Kowalevsky, 1872; Webb, 1983). This timing

would correlate with the end of the middle Miocene climatic optimum. This

interpretation for grassland expansion was based largely on the prevalence of mammals

with grazing adaptations, especially horses, and has been viewed as a classic example of

coevolution. Mesodont horses such as Parahippus gave way to hypsodont horses, like

M~erychippus and Hipparion, that also exhibited increased enamel folding and cement

deposition on the cheek teeth (Webb, 1977). These adaptations, which improved the

grinding surface of the tooth, were also featured in camels, pronghorns, oreodonts,

rhinoceroses (diceratherine and teleoceratine), and at least four genera of gomphotheriid

proboscideans (Webb, 1977). The diversification of these taxa is directly correlated to the

degree of hypsodonty; the higher-crowned lineages experienced greater radiations

(Webb, 1977). The succession of grazers, starting at the beginning of the Barstovian










(15.8 Ma) and lasting through the end of the Clarendonian (8.8 Ma), has been termed the

'Clarendonian chronofauna' (Webb, 1983). It has also been suggested that this faunal

succession (and therefore the appearance of grasses) began during the beginning of the

late Hemingfordian at 17.5 Ma (Theodor, Janis, and Broekhuizen, 1998).

In addition to dental adaptations for grazing, many ungulates acquired elongated

limb modifications for open-country locomotion (Webb, 1977). Hypsodont horses, for

example, developed digital springing ligaments at about the same time that they

developed grazing dentitions (Camp and Smith, 1942). Rodents also adapted to savanna

habitats in the Miocene. Their teeth became higher-crowned (Rensberger, 1973) and their

limbs adapted for burrowing habits (Webb, 1977). Mylagaulids (Fagan, 1960),

heteromyids (Lindsay, 1972), geomyoids (Rensberger, 1971), and ochotonid rabbits

(Green, 1972) all diversified into an array of hypsodont burrowers. The abundance of

needlegrass taxa, specifically Stipidium and Berriochloa, in the High Plains region (Elias,

1942) seemingly confirmed the dominance of grasslands in the Great Plains during the

middle Miocene.

The traditional view of grassland evolution was modified by a study of the late

Miocene (12-13 Ma) Kilgore Flora of Nebraska. This floral assemblage depicted an

environment consisting of savannas with mesic and open grassy forests, but lacking any

open prairies (MacGinitie, 1962). Faunal evidence corroborates this claim. The presence

of arboreal rodents, primates, insectivores, brachydont browsers and mixed feeders

suggests that the Great Plains was still a woodland savanna with riparian forests through

the late Miocene (Gregory, 1971). Grasses, therefore, were abundant through the late

Miocene, but grasslands had yet to dominate the landscape. It was not until the Late










Hemphillian (Early Pliocene, ~5 Ma), that treeless steppe grasslands swept across the

Great Plains. The vertebrate evidence for this consists of the absence of arboreal and

browsing taxa, a limited diversity of grazing taxa, and an overall lower diversity of all

vertebrate taxa (Gregory, 1971).

The traditional grassland story has been further modified, in more recent years,

from multiple types of studies. Paleosol studies indicate the presence of short sod

grasslands in the Great Plains region in the early Miocene, ~19 Ma, and tall sod

grasslands by the late Miocene, ~7 Ma (Retallack, 1997; Retallack, 2001). Paleosol

studies also indicate the presence of sod grasslands in the Hemingfordian (early Miocene,

~ 19 Ma) in central Oregon (Retallack, 2004). Phytoliths, the silica granules found in

many plants, have also been used to identify savanna environments. Morphological

studies on phytolith assemblages from northwestern Nebraska indicate that open-habitat

grasses were present in savanna and woodland environments by the early Miocene

(Stroimberg, 2002; Stroimberg, 2004).

The most extreme revisions have come from stable isotope studies. Stable carbon

isotopes from paleosols and fossil tooth enamel from various regions reveal a global

increase in the C4 biomass during the late Miocene and early Pliocene (7-5 Ma) (Quade

et al., 1992; Cerling, Wang, and Quade, 1993; Wang, Cerling, and MacFadden, 1994;

MacFadden and Cerling, 1996; Cerling et al., 1997b). This observation was based

primarily on the bioapatite of the fossil teeth, which reflect the C3 C4 plant constituents of

the animal's diet through 813C ratios. It was proposed that the increase in C4 biomass was

due to lowered concentrations of CO2 in the atmosphere, which would have caused the

less efficient C3 plants to diminish and the more efficient C4 plants (mainly tropical










grasses) to flourish (Ehleringer, Sage, Flanagan, and Pearcy, 1991; Cerling et al., 1993;

Cerling et al., 1997b). This theory has been countered by Morgan, Kingston and Marino

(1994), who claim that there was no expansion of the C4 biomass and no connection

between the atmosphere and any changes in the C3/ C4 biomass. Rather, Morgan and

colleagues suggest that the apparent increase in C4 COnSumption by mammalian

herbivores is the result of faunal immigration or in situ speciation, not a change in the

floral populations. Also, the proposed decrease in atmospheric CO2 COncentrations has

been challenged due to a lack of direct evidence of a change in the partial pressure of

CO2 (Pagani et al., 1999).

The isotopic evidence modifies the grassland story in two ways: (1) It pushes the

dominance of C4 graSslands back as early as 7 Ma and, more importantly, (2) Denies a

significant C4 preSence before 7 Ma, casting doubt on the idea that grassy savannas

preceded the steppe environment in the Great Plains. Initially, the isotopic and faunal

evidence provided an interesting dilemma. The faunal morphological changes suggested

a strong presence of grass, presumably C4, in the Great Plains at 15.8 Ma (Webb, 1983)

or 17.5 Ma (Theodor et al., 1998). However, a major global increase in C4 biomass is not

documented in the paleodiets until 7 Ma (Cerling et al., 1993). This indicates an apparent

change in faunal morphology that began 8.8 to 10.5 million years before the ungulates

began eating C4 graSses, and therefore long before the dominance of the grasses believed

to have caused the adaptations (Fox and Koch, 2003).

More recent isotopic evidence has addressed this discrepancy by pushing the

appearance of C4 graSses back prior to the original 15.8 Ma age based on faunal

morphology. Fox and Koch (2003) looked at paleosol stable isotopes from the Great









Plains region of North America and suggested that the C4 biomass first appeared no later

than the early Miocene (about 23 Ma), but did not become dominant until the late

Miocene (as evident from the biomass shift seen at 7 Ma). Based on the paleosol and

faunal data, Fox and Koch (2003) suggested that typical Great Plains habitats in the late

Miocene consisted of C3 trees and shrubs over a light carpet of grass.

The apparent temporal gap between grazer morphology and C4 dominance could

then be the result of the expansion of cool climate C3 graSses (Wang et al., 1994; Fox and

Koch, 2003). Expansive C3 graSses in the middle Miocene could have been responsible

for the ungulate grazing adaptations, since C4 graSses were still too relatively low in

abundance to cause such expansive adaptive radiations (Fox and Koch, 2003). The idea

of C3 graSses driving hypsodonty radiations denotes a paradigm shift in how paleodiets

are assessed through stable isotopes. Initially, 613C ValUeS that reflected C3 diets were

typically ascribed to browse material, such as shrubbery and leaves. C3-COnSumers were

then categorized as "browsers" while C4 COnSumers were categorized as "grazers." This

was due, in large part, to the assumption that paleoenvironments are analogous to modern

environments. This assumption has recently been reevaluated. Wang et al (1994) first

suggested that a unique grassland environment composed of low-latitude C3 graSSCS

could have existed in the middle Miocene due to lower concentrations of atmospheric

CO2. JaniS, Damuth, and Theodor (2002) concluded that early Miocene ungulates are

unlike any ungulates from modern grassland and forest environments and, therefore,

represent a paleoenvironment unlike any seen today. This interpretation has been

supported by Fox and Koch (2003), who proposed the hypothesis of expansive C3 graSSCS









in woodland environments. Woodland savannas with C3 graSses would then constitute a

unique environment with no modern analogues.

In order to further assess this claim, and to evaluate the spread of C4 graSses across

North America, this study focuses on the middle Miocene to early Pleistocene (15-5 Ma)

of northern/central Florida and southern Georgia and seeks the presence of grasses in the

diets of ungulates. Of particular interest is the Willacoochee Creek Fauna, an early

Barstovian (~15 Ma) faunal assemblage that is mostly composed of possible early grazers

or mixed feeders ungulatess bearing mesodont to hypsodont teeth). This faunal

community existed at a pivotal point in the evolutionary history of mammals; when open-

habitat morphologies rapidly expanded. This study utilizes three methods of paleodiet

analysis: stable carbon isotope analysis, mesowear analysis, and microwear analysis. The

combination of stable isotopes and mesowear or microwear makes it possible to either

substantiate or refute the presence of C4 graSses in the paleodiets of middle Miocene

ungulates, as well as address alternative driving mechanisms for the adaptation of

hypsodonty. The objectives of this study are (1) Characterize the dietary habits of the

community of herbivores from the Willacoochee Creek Fauna, (2) Determine the

presence of any grasses, C3 Of C4, in nOrthern Florida during the middle Miocene, and (3)

Determine the presence of any grasses, C3 Of C4, in Florida leading up to the carbon

biomass shift at ~7 Ma.















CHAPTER 2
FIELD AREA AND FAUNA

The taxa in this study were excavated from sediments from seven sites in Florida

and Georgia. Three of the sites are located in northern Gadsen County, Florida: the

Englehard La Camelia Mine, the Milwhite Gunn Farm Mine, and the La Camelia 2 Mine

(Figure 2-1). Sediment samples were collected from the Englehard La Camelia and

Milwhite Gunn Mines in the late 1980's by field crews from the Florida Museum of

Natural History (FLMNH) and the University of Florida Department of Geological

Sciences (Bryant, 1991). Vertebrate fossils were also collected from these sites. Most of

the fossils were recovered from spoil piles, but these piles were positively associated with

the Dogtown Member of the Torreya Formation (Bryant, 1991). These fossils comprise

the Willacoochee Creek Fauna (WCF) assemblage, an early Barstovian (middle Miocene)

assemblage of mammals, birds, amphibians, and reptiles found in the Dogtown Member

(Bryant, 1991). The early Barstovian designation of the assemblage is based on the

presence of Copemys, Perognathus, Rakomeryx, and Ticholeptus, as well as the

overlapping age ranges of several other mammals (Bryant, 1991; Table 2-1). The

beginning of the Barstovian is defined by the appearance of Copemys and the early

Barstovian is characterized by the appearance of Perognathus, Rakomeryx, and

Ticholeptus (Tedford et al., 1987). The WCF bears mammals with known age ranges that

begin in the early Barstovian, restricting the age of the WCF to an upper limit of early

Barstovian (Bryant 1991). The overlapping age ranges of other mammals, such as those









of the Merychippine horses, support this age correlation. The absolute age of the early

Barstovian is between about 16.6 to 14.4 Ma (Tedford et al., 1987).

The Torreya Formation is part of the Hawthorn Group and it is the only part of that

group that is present in the eastern Florida panhandle (Scott, 1988; Huddlestun, 1988).

The formation is siliciclastic with scattered carbonate and phosphate deposits and can be

found throughout the eastern Florida panhandle and into southern Georgia (Bryant,

1991). Bryant (1991) described the Dogtown Member of the Torreya Formation as

"largely clay, with varying amounts of sand and dolomite, and is primarily present in

Gadsen County, Florida, and adjacent Decatur County, Georgia" (Figure 2-2). The

Englehard La Camelia Mine was designated as the type section of the Dogtown Member

(Bryant, 1991). Vertebrate fossils are found in the sand and sand/clay layers (Figure 2-3).

As mentioned earlier, the Milwhite Gunn Farm Mine also belongs to the Dogtown

Member, but it represents a unique lithology. It consists of well-indurated, weathering-

resistant, carbonate-cemented sandstone (Bryant, 1991). Bryant (1991) suggested that the

outcrop at the Milwhite Gunn Farm Mine represented a "subaerial exposure surface, but

no pedogenic horizonation is preserved." The Milwhite Gunn Farm Mine and Englehard

La Camelia Mine layers are contemporaneous, based on the in situ presence of the

rodents Copemys and Perognathus at both sites (Bryant, 1991).

There are two new sites, the La Camelia 2 and Crescent Lake Mines. The La

Camelia 2 Mine is located in northern Gadsen County, Florida, near the original

Englehard La Camelia Mine site. Over 2,000 pounds of sediment, as well as some

vertebrate fossils, were collected from La Camelia Mine 2 by an FLMNH/UF Geology

Department field crew in May, 2004. Like the previous sites, the sediment samples and









fossils were collected from spoil piles at this site. These piles, however, were positively

associated with a single unit at the site. This unit consists of interfingering sand and clay

layers and has been correlated with the Dogtown Member and aged as early Barstovian.

The unit correlation is based on lithology and the Barstovian age, which is derived from

the overlapping presence of Aphelops sp., which first appears in the Late

Hemingfordian, and Acritohippus isonesus (Figure 2-2).

The second new site, the Crescent Lake Mine, is located 15 miles north of the

Florida-Georgia Border in Decatur County. Vertebrate fossils and sediment were

collected from this site by FLMNH Hield crews in May, 2005. Unlike the other sites, these

samples were collected in situ along a fresh cut at the mine (Figure 2-4). The sediments at

the Crescent Lake Mine constitute a clayey sand layer representing terrestrial and marine

environments. Marine depositional environments are evident by the presence of abundant

invertebrate fossils, such as gastropods, bivalves, and echinoids (sea urchins), as well as

garfish scales. Based on the lithology of the unit and mammal assemblage, this site

correlates with the Dogtown Member of the Torreya Formation and an early Barstovian

age. The age is based on the presence of the brachydont Anchitherium clarencei and the

mesodont M\~erychippus primus, two horses with biochronological ranges in the WCF that

extended, and terminated, in the early Barstovian (Bryant, 1991; Figure 2-2).

Additionally, the hypsodont horse Acritohippus isonesus and the rhino Aphelops have

overlapping ranges in the Barstovian (Bryant, 1991).

The two sites discovered in the 1980's (Englehard La Camelia and Milwhite Gunn

Mines) have both been analyzed for strontium-isotopic and paleomagnetic dating. Four

reliable sSr/86Sr age estimates place the Dogtown Member between 16.6 + 1.0 and 14.7









+1.5 Ma (Bryan, MacFadden, and Mueller, 1992). The Dogtown Member is entirely of

reversed polarity, and, with biochronologic data, the unit correlates with Chron C5B-R

(Bryant et al., 1992). This correlation narrows the age of the Dogtown Member, and

therefore the WCF, to between 16.2 and 15.3 Ma (Bryant et al., 1992). This range has

been restricted further, to between 15.9 and 15.3 Ma, based on the Hemingfordian-

Barstovian boundary (Woodburne, Tedford, and Swisher, 1990). Bryant et al. (1992)

also determined that the Dogtown Member is time-transgressive, with sediments getting

younger to the north.

In addition to the middle Miocene sites, this study looks at younger sediments to

trace the presence of grasses in Florida. The three younger sites are all located in central

Florida. Ages for two of these sites are determined by biochronology. The Love Bone

Bed Site is late Miocene and designated as late Clarendonian in age (~9.5 Ma) and the

Upper Bone Valley Formation is early Pliocene and late Hemphillian (~4.5 Ma) (Figure

2-5; Hulbert, 1992; Morgan, 1994). The accuracy of these ages is within about f 0.5 Ma

(MacFadden and Cerling, 1996). The third site is the Leisey Shell Pit, which has been

dated at approximately 1.5 Ma, based on biochronological, sSr/86Sr, and paleomagnetic

data (Webb et al., 1989). The accuracy of this age is about f 0. 1 Ma and places the

Liesey Shell Pit in the early Pleistocene with an early Irvingtonian age (Figure 2-5).

These three sites were chosen for this study because stable carbon isotope analyses have

been previously conducted on large populations of fossil horses from these sites

(MacFadden and Cerling, 1996). These large populations are also ideal for mesowear

analyses.









The specimens analyzed in this study span approximately 14 million years.

Specimens from the Englehard La Camelia, Milwhite Gunn Farm, and La Camelia 2

Mines are representatives of the WCF from the Dogtown Member of the Torreya

Formation and are of early Barstovian (about 15.9 to 15.3 Ma) age (Bryant, 1991).

Before any analyses could be conducted, it was necessary to identify all of the

specimens. Despite the previous description of the WCF by Bryant (1991), many of the

collected fossils were still unidentified and not catalogued. Additionally, all of the fossils

from the new site needed to be identified and catalogued. These fossils, which are all

teeth, were identified by referencing published literature as well as identified specimens

from the FLMNH collections. The vast maj ority of unidentified specimens were horse

teeth. In addition to identifying the taxon, the tooth position was determined for each

tooth by comparing the widths of the parastyle and mesostyle and assessing the angle of

the mesostyle and plane of occlusal surface (Figure 2-6). Typically, the parastyle is wider

than the mesostyle in horse molars and vice versa for horse premolars (Bode, 1931).

More posterior-leaning mesostyle angles and shallower angles of the occlusal plane are

indicative of molars, while more anteriorly-leaning mesostyles and more pronounced

angles of the occlusal plane are apparent in premolars (Bode, 193 1). Identification of the

tooth position is important in this study since paleodiet analyses often use specific teeth

as a standard for paleodiet assessment.
































Figure 2-1. Index map of middle Miocene localities in northern Florida. 1 = Milwhite
Gunn Farm Mine, 2 = Englehard La Camelia Mine and La Camelia 2 Mine.
All of the Willacoochee Creek Fauna taxa were collected from the Dogtown
Member of the Torreya Formation. (Modified with permission from Bryant,
1991)


STOAlREYA FM.

DO GTOWNY MB1











Table 2-1. Biochronological ranges of the Willacoochee Creek Fauna. Solid lines
indicate known ranges and asterisks indicate range extensions. Note that all of
the ranges overlap in the early Barstovian. Also, Ticholeptus hypsodus,
Bouromeryx of. parvus, and Rakomeryxr sp. all occur only in the early
Barstovian. These ranges denote an early Barstovian age for the Dogtown
Member of the Torreya Formation. (Modified with permission from Bryant,
1991)
TAXON HEMINGFORDIAN BARSTOVIAN CLARENDONIAN
EARLY LATE EARLY LATE EARLY LATE
Lanthanotheriumsp ****
Mylagaulus sp.
cf. Protospermophilus sp.
Perognathus cf. minutus
Proheteromys sp.
Copey p
yoc" cf. proterva
Ticholeptus hypsodus
Bouromeryx cf. parvus

Anchitherium clarencel ****
Merychippus gunteri
Merychippus primus
Acritchippus isonesus
Aphelops sp.
KNOWN BIOCHRONOLOGICAL RANGE
wwwwwww BIOCHRONOLOGICAL RANGE EXTENSION










COMPOSITE SECTION









10O m








carbonate
Sclay/sand [sand clay E3cement


Figure 2-2. Composite section of the Torreya Formation and the location of the
Willacoochee Creek Fauna within the Dogtown Member. Note that the
Dogtown member is composed mostly of clayey sand and some clay.
(Modified with permission from Bryant, 1991)













LA CAMELIA
MINE


GUNN FARM
MINE


- m


( SAND
I SAND/CLAY
C CLAY
tt CABONTATE


**B VERTEBRATE FOSSIL HORIZON


Figure 2-3. Correlated stratigraphic sections of the Englehard La Camelia and Milwhite
Gunn Farm Mines. Note that the Willacoochee Creek Fauna are found in
layers composed of clayey sand, sand, and sand with carbonate cement.
(Modified with permission from Bryant, 1991)




























~C-ulN~~ Cy~.J:
r -r --


B)






Figre2-. reh utat henees ste te resent~ LaeMie i eatrCony



Georga. A)Crosssectin vie of snd an cla laye~' J~ris aov hefoslieru
layer. B) Bottom of th cut, where the fossiiferos caye ad sepoe.I
the oreroun iswhee teresrialverebrte fssis wee fund whie mrin
invertebrate were- fon lehr ntect
















FIANGHEM~BRE.II

IRCVIt~FLN IhlA
LEI;SE Y....





BONE VALLEY
5iL


MOSS ACRES HEMPIIL.I.JAN




LIOVE BONE BED -i

CI.4TIEP JAN





Figure 2-5. Stratigraphic and temporal distribution of the 3 fossil sites studied in the
mesowear analysis, as well as a fourth (Moss Acres) discussed later.
Neohipparion trampa~sense, Cormohipparion plicatile, and Cormohipparion
ingenuum are from the Love Bone Bed, Nannippus aztecus is from the Upper
Bone Valley Formation, and Equus "leidyi" is from the Leisey Shell Pits.
(Modified with permission from MacFadden and Cerling, 1996)




























A)

Mesostyle Pastl
Parastyle Mesostyle




I r'I




Anteror Poterio
B).


Figur 2-6 Tot o'in. )Temdr hrl a ih h nlso emssye






p)~tremola a n pe or ~ (b. oe h dferecsin aasyen

Figre -.mesh os~tylidths and the mdiferencres in ange oft the panges of occlussayle
srandoc.sa (Modfied with permissionh fritom. Bodre, itos 1931)per















CHAPTER 3
MESOWEAR METHOD

The mesowear method was devised by Fortelius and Solounias (2000) as a quick

and inexpensive process of determining the lifelong diet of a taxon. They determined

that, for extant mammals, broad conclusions on the diets, such as a grazer or browser

classification, can be deduced from the shape of the buccal cusps (either the paracone or

metacone) and the relative difference in height between the tip of the cusps and the

intercusp valley. The robustness of this method was confirmed by blind test studies that

revealed that there are no statistical differences in the scoring of attributes between

individual researchers (Kaiser et al., 2000).

The attributes that are evaluated, termed cusp shape and occlusal relief, were

originally only applied to the upper second molar (M2) and require at least 20 specimens

to obtain a reliable classification. Fortelius and Solounias (2000) used cusp shape and

occlusal relief to establish a "typical" set of 27 extant browsers, grazers, and mixed

feeders. This set was illustrated in a hierarchical cluster analysis (Figure 3-1), which

shows clusters of mammals that had similar wear (attrition- or abrasion-dominated). The

classification of each cluster ("e.g.", grazerr") was confirmed by direct observations

made on the diets of the animals. The mesowear technique can be extended to an extinct

taxon, which can then be included in the hierarchical cluster analysis to determine its

dietary classification. Mesowear analyses require large sample populations (>20), which

can be problematic for some localities, but the method yields an accurate depiction of an

animal's average lifelong diet.









In a study on hipparionine and extant equids, the mesowear method was "extended"

to broaden its application beyond the upper M2, to specific combinations of the upper

third premolar (P3), upper fourth premolar (P4), upper first molar (M1), and the upper

third molar (M3) (Kaiser and Solounias, 2003). This study was conducted with the goal

of expanding the application of the mesowear method beyond ungulate populations with

an abundance of M2s. The "extended" mesowear method, the combination of tooth

positions that yielded results most consistent with the M2 results, was that of the

P4+M1+M2+M3 teeth.

However, the "extended" method still requires positive identification of the tooth

positions. While this is not problematic when studying associated teeth, it can be difficult

to identify isolated teeth. This is especially true for equids. Bode (1931) showed that it

was possible to identify tooth position of unassociated teeth through the anterior-posterior

tilt of each tooth, but it has been noted that this method is time-consuming and does not

always result in a positive identification (Hulbert, 1987). This problem is often

encountered when trying to distinguish between a P3 and P4. Kaiser and Solounias

(2003) showed that the P3 in hipparionine equids was an unreliable indicator of paleodiet,

causing a shift towards a grazer classification. Additionally, they showed that the P4 is a

reliable indicator, particularly when grouped with molars (as in the "extended"

combination of P4-M3). To ensure correct dietary classifications based on unassociated

teeth, this study will apply the mesowear method only to molars, avoiding dubious

premolars. Previous studies have shown that analyses based on Mis and M2s yield the

same classifications as analyses based on only the M2s (Kaiser and Solounias, 2003;

Hoffman, unpublished).









Materials and Methods

Mesowear analyses were conducted on five equids from the younger central Florida sites:

Neohipparion trampa~sense, Cormohipparion plicatile, and Cormohipparion ingenuum

from the Love Bone Bed Site (~9.5 Ma); Nannippus aztecus from the Upper Bone Valley

Formation (~4.5 Ma), and Equus "leidyi" from the Leisey Shell Pit (~1.5 Ma) (Table 3-

1). Based on dental and post-cranial morphology, Neohipparion trampa~sense is a

probable grazer to mixed feeder while the Cormohipparion species are both expected to

be mixed feeders (MacFadden and Cerling, 1996). The taxon analyzed from the Upper

Bone Valley Formation is Nannippus aztecus, an expected grazer. Finally, Equus

"leidyi," an extremely hypsodont grazer from the Leisey Shell pit, was also analyzed.

Following the techniques described in Fortelius and Solounias (2000), the cheek

teeth of six different taxa were assessed for mesowear analysis, in terms of cusp shape

and occlusal relief (Figure 3-2). The cusp shape rating (sharp, round, or blunt) describes

the shape of the apex of the sharper cusp. The occlusal relief describes the height of the

cusps (high or low) relative to the valley between them. This rating can be quantified by

drawing a line that connects the apices of the two cusps, then measuring the vertical

distance between that line and the center of cusp valley. This value is then divided by the

length of the whole tooth. For equids, values greater than 0. 1 signify high occlusal relief

and values below 0. 1 signify low occlusal relief (Fortelius and Solounias, 2000). To

avoid teeth that were in the early or late stages of wear at time of deposition, only teeth

that are 25% to 75% of the maximum crown height were analyzed. Waterworn teeth were

also excluded from the sample set. When necessary, a magnifying lens was used in rating

the attributes.









As stated in Fortelius and Solounias (2000), the mesowear signal becomes stable

when there are more than 20 teeth, although a reasonable approximation is attained at

about 10 samples. In this study, at least 20 samples were measured for each taxon to

ensure correct classifications. The teeth that were analyzed include positively identified

Mis and M2s, as well as molars that could be either an Ml or an M2. Once the

measurements were recorded, the percentages for each attribute were calculated. Next,

these percentages were examined by hierarchical cluster analyses, using SPSS v. 11.5

software, to determine the dietary classification of each taxon. The variables entered into

the hierarchical cluster analyses are percentage high occlusal relief, percentage sharp

cusp shape, and percentage blunt cusp shape. Complete linkage and normalized

Euclidean distance were used in the analysis, following Fortelius and Solounias (2000).

Each taxon was entered into a separate cluster analysis, to avoid altering the morphology

of the dendrogram and possibly yielding biased clusters. The cluster placement of each

fossil taxon was used to determine its dietary classification. For example, a taxon that is

located within the cluster of 'typical' extant grazers would be classified as a grazer.

Results

The cusp shape and occlusal relief ratings for each sample are listed in the

Appendix A. The calculated percentages of the attribute ratings for each taxon are listed

in Table 3-2. In the hierarchical cluster analyses, all Hyve horses (Neohipparion

trampasense,~rtrtrtrt~t~t~ Cormohipparion plicatile, Cormohipparion ingenuum, Nannippus aztecus,

and Equus "le/Jyr )~~ are placed within the cluster of confirmed extant grazers (Table 3 -3,

Figure 3-3). N. trampasenser~rtrtrtrt~t~t~ clusters closest to Ceratotherium simum (White rhinoceros),

while C. plicatile is closest to Damnaliscus lunatus (topi) and C. ingennum is placed

closest to the subcluster of Alcelaphus buselaphus (hartebeest) and Connochaetes










taurinus (wildebeest). Conversely, N. aztecus forms its own sub cluster with Alcelaphus

buselaphus, placing closer than Connochaetes taurinus. Finally, E. "ledivi" is placed

closest to Bison bison (American plains bison). All of these extant herbivores are typical

hypsodont grazers.










0 5 10 15 20 25
+---------+---------+---------+---------+-----
















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Fiur 3-.Dnrga lutaigteheaciclcutraayi fte2 tpcl

grzes brwes n ie edr rm otlu n oona 20)
Brwe brvain r nuprcse rzrabeitosaei oe
cae n ie edrabrvain r pe n lwrcs.Abeitos
A =Acesacs S hnceo odiuD =Dieo ions V
Odciesvriins J kpajhntnG =Grfacneoadls
OH Odcilu hezouD=Dceohnssnaress g ael
grati Gt ael hnsni m vbsnocats o artau





hiso










Table 3-1. Systematic and morphological information about the taxa used in the
mesowear analysis. Abbreviations: MSCH = Maximum crown height
measured from the occlusal surface to the base of the crown along the
mesostyle. (N. trampasenser~rtrtrtrt~t~t~ tribe, age, and MSCH data from Hulbert, 1987; C.
plicatile and C. ingenuum tribe, age, an MSCH data from Hulbert, 1988; N.
aztecus tribe, age and MSCH data from Hulbert, 1988 and Hulbert, 1990;
Equus "leidyi" tribe, age, and MSCH data from Hulbert, 1995).

Molar Tooth
Taxon Tribe Site and Ag~e Level MSCH Morpholog
Nohipparion trampasense Hipparionini Love Bone Bed, ~9.5 Ma 60 mm Hypsodont
Cormohipparion plicatile Hipparionini Love Bone Bed, ~9.5 Ma 58 mm Hypsodont
Moderately
Cormohipparion ingenuum Hipparionini Love Bone Bed, ~9.5 Ma 49 mm
hypsodont
Nanppus aztecus Hipparionini Upper Bonie Valleyi Fm., ~4.5 Ma 51 mml Mdrtl
hypsodont
Eus"leidyi" Equinni Liesey Shell Pit, ~1.5 Ma 91.3 mm Extremelyhysdn






Ilaw


















siharlp round blunt
Cusp Shrape (C: 5)

Figure 3-2. Examples of typical mesowear attributes. The three types of cusp shape are
sharp, round, and blunt. The types of occlusal relief are high and low. The
dotted lines indicate the height of the occlusal relief, from the bottom of
intercusp valley to the apex of the highest cusp. (Modiefied with permission
from Kaiser and Fortelius, 2003)










Table 3-2. Observed percentages of mesowear attributes (% high and % low refer to the
percentage of specimens with high or low occlusal relief and % sharp, %
round, and % blunt refer to the percentage of specimens with sharp, round or
blunt cusp shape).

% % % % %
Taxon N high low sharp, round blunt

Neohipparion trampasense 49 24.5 75.5 2 57.2 40.8

Cormohipparion plicatile 45 35.6 64.4 8.9 60 31.1

Cormohipparion ingenuum 26 50 50 0 84.6 15.4

Nannippus aztecus 35 54.3 45.7 0 82.9 17.1

Equs leidyi 30 0 100 6.7 20 73.3


Taxon Site Age Classification


Nohipparion trampasense Love Site 9.5 & 0.5 Ma Grazer

Cormohipparion plicatile Love Site 9.5 & 0.5 Ma Grazer

Cormohipparion ingenuum Love Site 9.5 & 0.5 Ma Grazer

Nanppus aztecus Upper Bone Valley Fm. 4.5 & 0.5 Ma Grazer


Equs leidyi Leisey Shell Pit 1.5 & 0.1 Ma Grazer


Table 3-3. Dietary classifications based
attributes from Table 3-2.


on hierarchical cluster analyses of mesowear










Bescalec1 Distance Cluster Combine
0 5 10 15 20 25
+---------+---------+---------+---------+-----


Figure 3-3. Dendrograms illustrating the hierarchical cluster analyses of 6 studied taxa
amongst the 27 'typical' grazers, browsers, and mixed feeders from Fortelius
and Solounias (2000). A) Neohipparion trampasenser~rtrtrtrt~t~t~ (Nt). B)
Cormohipparion plicatile (Cp). C) Cormohipparion ingenuum (Ci). D)
NNNNNNNNNNNNNNNNNNNNanipu aztecus (Na). E) Equus "leidyi" (El). Note that all five equids place
within the "Grazers" cluster. Browser abbreviations are in upper case, grazer
abbreviations are in lower case, and mixed feeder abbreviations are in both
upper and lower case. Abbreviations: AA= Alces alces, RS= Rhinoceros
sondaicus, DB= Diceros bicornis, OV= Odocoileus virginianus, OJ= Okapia
johnstoni, GC= Giraffa camnelopardalis, OH= Odocoileus hemionus, DS=
Dicerorhinus sumatrensis, Gg= Galzella granti, Gt= Galzella thomsoni, Om=
Ovibos moschatus, To= Taurotragus oryx, Ts= Tragelaphus scriptus, Cc=
Cervus canadensis, Cs= Capricornis sumatraensis, Me= Aepyceros
melampus, ab= Alcelaphus buselaphus, ct= Connochaetes taurinus, he=
Hippotragus equinus, rr- Redunca redunca, ke= Kobus ellipsipyrmnus, hn=
Hippotragus niger, eb= Equus burchelli, eg= Equus grevyi, dl= Damnaliscus
lunatus, cs= Ceratotherium simum, bb= Bison bison.














Bescalec1 Distance Cluster Combine

0 5 10 15 20 25
+----------- ---- -+- ---- --- -+-- --- ----+-- --- ---- +


Rescaled Distance Cluster Combine

0 5 10 15 2~ 0 5
+----------- ---- -+- ---- --- -+-- --- ----+-- --- ---- +


T;o~





Becalc1lc Distance Cluster Combine
5 10 15 2 0


Rcscalec1 Distance Cluster Combine


Q3 DB

C il















CHAPTER 4
MICROWEAR METHOD

The microwear method is a dietary analysis that quantifies the microscopic wear on

herbivore teeth. The consumption of herbivorous diets leaves microscopic scratches and

pits on the tooth enamel known as microwear. Studies on microwear of extant herbivores

with known diets have revealed a correlation between microwear and diet (Teaford and

Walker, 1984; Grine, 1986; Teaford, 1988; Solounias and Hayek, 1993) One noticeable

trend is that grazers typically have more scratches than browsers while browsers bear

more pits than grazers (Solounias and Semprebon, 2002). These observations have led to

the establishment of a Microwear Index (MI) (MacFadden, Solounias, and Cerling,

1999). For a stated area of enamel ("e.g.", 0.5mm x 0.5mm), the MI is calculated as the

total number of scratches divided by the total number of pits. As a standard, an MI below

1.5 indicates a browsing diet and an MI above 1.5 indicates a grazing diet (MacFadden et

al., 1999). Additional conclusions can be drawn by comparing the analyzed tooth to a

database of the microwear of extant animals with observed known diets. Plots of the

number of pits versus the number of scratches for these extant herbivores reveal distinct

morphospaces indicative of browsing, grazing, and mixed diets (Solounias and

Semprebon, 2002).

Microwear studies were initially conducted at high magnification using Scanning

Electron Microscopy (SEM) imagery (Grine, 1986). Recently, however, a low-

magnification technique was developed to reduce the time and financial costs of the

microwear method. Analyzing microwear at only 35x magnification has been shown to










reveal the same results as high magnifieation (Solounias and Semprebon, 2002).

Solounias and Semprebon (2002) also created four additional quantifying characters to

attain a more detailed understanding of dietary habits. These characters can be used in

hierarchical cluster analyses to determine which kind of extant herbivores most closely

resemble the fossil taxa in terms of microwear, and therefore diet. However, microwear is

subj ect to the "Last Supper Effect," the limitation of reflecting an individual's last few

meals, rather than the life-history of diet (Grine, 1986). Therefore, microwear analyses

are based on the assumption that the animal's typical diet is reflected by these Einal

meals.

Materials and Methods

Microwear analyses were conducted on three samples of the most hypsodont taxon

from the WCF assemblage, Acritohippus isonesus. Microwear analyses were conducted

instead of mesowear because of the small sample size. The standard tooth position for

microwear analysis is the second molar (upper or lower) (Solounias and Semprebon,

2002; Rivals and Deniaux, 2003). No other horses, such as M~erychippus primus or

M~erychippus gunteri, from the WCF were analyzed for microwear because there are not

enough M2s for a statistical analysis. Due to the very limited sample size of the WCF,

only one tooth ofA. isonesus (part of an associated dentition) was positively identified as

a second molar (M2). The other two samples were identified as first or second molars

(M1/2s). Based on the curve of the mesostyle, it appears likely that both of these teeth are

second molars, but it cannot be stated with certainty. Statistical analyses, such as the

unpaired Students t-test and nonparametric Mann-Whitney test, were conducted on the

collected results to determine whether there exist significant differences between the

M1/2s and the one positively identified M2. Microwear analyses were also conducted on










specimens of the hypsodont horse, Neohipparion trampasense,~rtrtrtrt~t~t~ from the Love Bone Bed

site (~9.5 Ma) of north central Florida. These microwear results were used for

comparison to A. isonesus.

This study followed the procedure for microwear analysis outlined in Solounias and

Semprebon (2002). The first step is to clean the occlusal surface of each tooth using 95%

alcohol and cotton swabs. A mold is then made of the tooth using high-precision

polyvinylsiloxane dental impression material. The mold is removed and discarded in

order to remove any remaining debris from the enamel. A second mold is then made.

After the second mold has hardened, it is used to make a clear, high-quality epoxy cast

(using a resin to hardener ratio of 5:1). After 1-2 days, the cast has hardened and is ready

for analysis.

The standard for microwear analysis consists of looking at a 0.4 mm x 0.4 mm area

of the cast under 3 5x magnification (Solounias and Semprebon, 2002). Those dimensions

(0.4mm x 0.4mm) were used because the objective crosshairs had 0.4 mm increments at

that magnification. It should be noted that the only stereomicroscope with crosshairs

available for this study had 50x magnification, not 35x. Additionally, the crosshair

increments had larger spacing, causing the search area to be larger, about 0.5mm x 0.5

mm. The increased magnification and search area result in higher numbers of scratches

and pits than would be found using the standard magnification and search field. While

this has no effect on the calculated ratio of scratches to pits or on the percentages of other

quantitative categories, the increase in average pit and scratch numbers prevents the use

of hierarchical cluster analyses to assess dietary subcategories. However, these










subcategories are not essential for this study, which is only concerned with whether the

taxa were eating grass or browse.

To observe the micowear features, a light source is shone through the cast at a

shallow angle to the occlusal surface. The casts are analyzed in a dark room and

adjustments to the intensity and angle of the light source are often made to best observe

the microwear features. Two 0.5 mm x 0.5 mm areas were assessed for each tooth.

Following Solounias and Semprebon (2002), these areas were located along the shear

facet of the second enamel band on the paracone of each upper tooth. For lower teeth, the

search areas were restricted to the shear facet on the protocone. Pits are defined as

microscopic defects in the enamel that have a length:width ratio < 4, while scratches are

defects that have a ratio > 4 (Grine, 1986; Teaford and Robinson, 1987). These categories

are obvious under low magnification. Pits usually appear as fairly round dots with a

length:width ratio of about 1 or 2, while scratches are always much longer and typically

have length:width ratios much higher than 4. For each tooth, the pit and scratch numbers

from the two search areas are averaged. Pits are further classified as large or small. Small

pits are the most numerous type and are fairly rounded. There are usually a few pits that

are at least twice the diameter of the small pits. These are categorized as large pits and

appear deeper and dark due to less refraction. Scratches are subdivided into fine or

coarse. Fine scratches are the narrowest scratches. They are shallow and often are white

from light reflection. Coarse scratches are often dark and longer than most fine scratches.

It is also noted when a sample bears more than four cross scratches. Cross scratches are

any scratches that run roughly perpendicular to the maj ority of scratches. Finally, the

average microwear index for each taxon is calculated.









Results

The observed counts of microwear features for each specimen are recorded in Table

4-1 and the calculated MI and percentages are presented in Table 4-2. Table 4-1 follows

the format and uses some of the quantitative parameters established by Solounias and

Semprebon (2002). The average number of pits and scratches for each taxon is listed,

followed by the microwear index (the ratio of scratches to pits), and two of the newer

quantitative variables. Since the microscope field used in this study is not the commonly

used size, these variables cannot be utilized in cluster analyses to determine more detailed

similarities to the diets of extant mammals. However, these variables are helpful in

making general inferences. The listed percentages in Table 4-2 for each of these attributes

refer to the percentages of specimens that bear that corresponding attribute.

Unpaired Students t-tests and nonparametric Mann-Whitney tests were used to

examine the concordance of the three A. isonesus specimens. The MI' s of the two

dubiously identified teeth (UF 223080 and UF 223081) were compared to the MI of the

positively identified M2 (UF 223063). The Students t-test and Mann-Whitney p-values

for comparing UF 223080 UF 223063 are 0.6826 and 0.4386, respectively. The Students

t-test and Mann-Whitney p-values for comparing UF 223081 to UF 223063 are 0.2195

and 0. 1213, respectively. For both of the M1/2 specimens, the Mann-Whitney test and

Students t-test yield p-values greater than 0.05 and reveal no significant differences

between the MI's. For each sample of both A. isonesus and N. trampa~sense, the average

number of scratches is almost double the average number of pits. The average MI's for A.

isonesus and N. trampasenser~rtrtrtrt~t~t~ are 1.97 and 1.98, respectively. The MI' s ofA isonesus and

N trampa~sense were compared for statistical differences using an unpaired Students t-test

and nonparametric Mann-Whitney test. The p-values for the Students t-test and Mann-










Whitney test are 0.5707 and 0.8690, respectively. These p-values are greater than 0.05

and show that the MI's of A. isonesus and N. trampa~sense are not statistically distinct.

Additionally, all of the samples for both taxa had scratches that were predominantly fine.

Each sample also had at least four cross scratches.













Table 4-1. Individual microwear counts for 3 specimens ofdcritohippus isonesus and 7
specimens of Neohipparion trampasense. Each specimen has two areas (A
and B) assessed for microwear. Abbreviations: UF ID = catalogue number in
the Florida Museum of Natural History collections, # x-scratches = number of
cross-scratches.

# fine # coarse
Taxon flF IE) # pits # scratches # x-scratches scratches scratches
Acritohippus 223063A 22 86 39 83 3
isonesus 223063B 43 96 20 81 15
223080/< 17 58 16 53 5
223080B 37 57 10 53 4
223081/< 83 118 27 110 8
223081B 65 111 40 106 5

Nohipparion 27991A 29 70 15 62 8
tapsense 27991B 42 48 13 45 3
27992;\ 45 59 26 55 6
27992B 22 57 17 52 5
27993/< 11 34 18 28 6
27993B 23 39 5 35 4
32280A 68 103 31 98 5
32280B 42 76 16 67 9
32291/< 25 49 9 48 1
32291B 24 85 25 79 6
36287A 29 58 26 53 5
36287B 30 69 25 58 11
32114A 37 103 17 99 4
32114B 32 60 18 54 6










Table 4-2. Calculated average microwear values and percentages for Acritohippus
isonesus and Neohipparion trampasense.~rtrtrtrt~t~t~ Abbreviations: N = sample size,
Avg. # pits = the average number of pits for the sample population, Avg. #
scratches = the average number of scratches for the sample population, MI =
microwear index, % Fine scratches = the percentage of the sample population
that possess scratches that are predominantly fine, % coarse scratches = the
percentage of the sample population that possess scratches that are
predominantly coarse, % cross scratches = the percentage of the sample
population that exhibits at least 4 cross scratches.

Avg. Avg. % Fine % Coarse % Cross
Taxon N # pits # scratches MI scratches scratches scratches
A. isonesus 3 44.5 87.67 1.97 100 0 100
N.trampasense 7 32.79 65 1.98 100 0 100

Table 4-3. Isotopic data for equids from 4 central Florida sites. Abbreviations: UF ID =
catalogue number in Florida Museum of Natural History collections.
(Modified from MacFadden and Cerling, 1996)


Taxon Site UF ID Material 613 (ooo

9.5 Ma Level, late Clarendonian, late Miocene
Nohipparion trampasense Love Bone Bed 32230 R. P3- 3 -11.6
Cormohipparion plicatile Love Bone Bed 32265 R. P2 -12.6
Cormohipparion plicatile Love Bone Bed 32265 R. P3 -12.5
Cormohipparion plicatile Love Bone Bed 32265 R. P4 -11.0
Cormohipparion plicatile Love Bone Bed 32265 R. M' -12.0
Cormohipparion ingenuum Love Bone Bed 60396 R. P2 -10.8
Cormohipparion ingenuum Love Bone Bed 35979 R. P2 -10.8

7.0 Ma level, "middle" Hemphillian, late Miocene
Nannippus aztecus Moss Acres 69933 R. M3 -7.9
cf. Nannippus Moss Acres None R. p2 -5.3

4.5 Ma level, latest Hemphillian, early Pliocene
Nanppus Upper Bone Valley None L. M -6.0
Nannippus aztecus Upper Bone Valley 63633 L. M2 -9.1
Nannippus aztecus Upper Bone Valley 65796 R. M' -2.4

1.5 Ma level, early Irvingtonian, early Pleistocene
Eq~uus "leidyi Leisey 1A 80047 R. M3 -1.5
Equs leidyi Leisey 1A None R. P2 -3.5















CHAPTER 5
STABLE ISOTOPE ANALYSIS

Background

Plants utilize three different types of metabolic pathways to process and use carbon.

These pathways are: the C4 pathway (or Hatch-Slack cycle), the C3 photosynthetic

pathway (the Calvin cycle), and the CAM (Crassulacean acid metabolism) pathway

(Bender, 1971). The C4-dicarboxylic acid pathway utilizes CO2 through carboxylation of

phosphoenolpyruvate (O'Leary, 1988). The Calvin Cycle, used by C3 plants, uses the

enzyme ribulose biphosphate carboxylase to fix CO2 (O'Leary, 1988). The CAM

pathway also uses ribulose biphosphate carboxylase to take in CO2, but the process is

more similar to what happens in the bundle sheath cells of C4 plants (O'Leary, 1988).

Plants that use the C4 pathway are primarily tropical grasses, but also include some fruits

and vegetables (O'Leary, 1988). C3 plants include trees, shrubs, and cool-climate

grasses, and dicots (O'Leary, 1988). The CAM plants consist primarily of desert

succulents (O'Leary, 1988).

Each plant metabolic pathway results in the isotopic fractionation of carbon (Figure

5-1) as it is taken into the plant cells from CO2 (Bender, 1971). The heavier carbon

isotope, 13C, iS discriminated against to varying degrees dependent on the pathway used,

and the 13 /12C iSotopic ratios of plants decreases relative to atmospheric isotopic ratios

(Bender, 1971). The lighter isotope is preferentially used due to the physical and

chemical properties associated with its mass (O'Leary, 1988). The carbon isotopic ratio









(813C) is represented as the parts per thousand difference between the sample and a

standard, the Peedee Belemnite from South Carolina (Craig, 1957).

C3 plants have an average 613C Value Of -27.1l%o f 2.0%o and a range from about

-3 5%o to -22%o, while C4 plants have an average 613C Value Of -13.1l%o f 1.2%o and have a

more limited range from -14%o to -10%o (O'Leary, 1988). CAM plants have a range of

-10%o to -20%o that distinguishes them from C3 plants, but not C4 plants (O' Leary, 1988).

Since CAM plants are known to be dominant only in xeric habitats (Ehleringer et al.,

1991), they are typically not considered in paleodiet analyses of temperate or subtropical

p al eoenvi ronm ents .

When mammalian herbivores consume plants, the carbon isotopes are fractionated

once again. By determining the fractionation factor for the mammal in question, the

carbon isotopic signature can be used to determine the diet, in terms of C3 and C4

consumption, of the herbivore. Stable carbon isotope analyses were first used in

archaeology to determine the paleodiets of ancient human populations (MacFadden and

Cerling, 1996). These studies analyzed the inorganic apatite in bone, which exists

primarily as hydroxyapatite, or Calo(PO4)6(OH)2 (Hillson, 1986; Wang and Cerling,

1994; MacFadden and Cerling, 1996). Trace amounts of carbon are present in this

mineral when it is commonly altered during skeletal formation, with carbonate (CO3 -2

replacing phosphate to yield Callo(PO4,CO3)6(OH)2 (Hillson, 1986; Newesely, 1989;

McClellan and Kauwenbergh, 1990). Due to the porous nature of bone collagen, the

hydroxyapatite with structural carbonate is extremely susceptible to diagenetic alteration

(Quade et al., 1992). Dental enamel, however, is much more resistant to diagenesis

because it is has very low porosity and is more than 96% inorganic by weight (Quade et










al., 1992; Wang and Cerling, 1994). Additionally, enamel is more than 95%

hydroxyapatite (Hillson, 1986). Multiple studies have found that the biogenic apatite of

enamel does not undergo diagenesis in most depositional situations and therefore retains

primary isotopic values (Quade et al., 1992; Wang and Cerling, 1994).

Cerling and Harris (1999) determined an enrichment factor of +14. 1 f 0.5%o

between the 613C Of the plants consumed and the bioapatite in the enamel of extant

ruminant mammals. This consistent enrichment establishes distinct ranges of isotope

ratios for ruminants that consume C4 Of C3 plants. Grazers (animals that feed primarily

on C4 graSses) fall in a range of 0%o to +4%o while browsers (animals that feed off of

leaves from C3 Shrubs and trees) fall within a range of -21%o to -8%o (Cerling and Harris,

1999). Stable carbon isotope analyses can therefore be conducted on ruminant teeth to

determine diet. This method has been extended to extinct ruminants to determine a

general classification of feeding habit. To do this, paleodietary analyses have adopted the

categories used to describe extant herbivores, established by Hofmann and Stewart

(1972). There are three general categories: concentrate selectors (browsers), bulk and

roughage feeders (grazers), and intermediate feeders (mixed feeders that consume both

browse and grass) (Hofmann and Stewart, 1972). These categories have been subdivided

further to detail the complexity of the feeding strategy. These subdivisions, however, are

rarely used in paleodiet analyses because it is difficult to calculate percentages of plant

type for an extinct animal. It is also important to recognize that paleodiet studies that

utilize stable isotope analyses rely on two assumptions: 1) The metabolic pathways of the

plants behaved similarly in the past as they do today ("i.e.", fractionated to the same









degree), and 2) the metabolic pathways and enrichment factor of ruminant mammals have

been consistent throughout time.

There is another factor that must be corrected when analyzing stable carbon

isotopes in fossils. As stated above, the 613C ValUeS of modern ruminants are derived

from the fractionation of carbon from plant intake, which is fractionated from the fixation

from atmospheric CO2. Atmospheric 613C ValUeS have decreased from approximately

-6.5%o to approximately -8.0%o over the course of the last 200 years, due to the burning

of fossil fuels (Friedli, Loitscher, Oeschger, Siegenthaler, and Stauffer, B, 1986; Marino,

McElroy, Salawitch, and Spaulding, 1992). Due to this change in atmospheric 613C

values, fossil bioapatite values are about 0.5%o to 1.3%o more positive than the values of

modern mammals (Koch, Hoppe, and Webb, 1998). This adjustment shifts the

endmembers on the scale for paleodiet interpretation: a diet strictly consisting of C3

plants would be no more positive than -8.7%o and a pure C4 diet would be no more

negative than -0.5%o (Feranec, 2003). Using these endmembers, a browser (less then 10%

C4 intake) would have a 613C Value leSs than -7.9%o, a grazer (less than 10% C3 intake)

would have a 613C value greater than -1.3%o, and a mixed feeder would have a 613C ValUe

between -7.9%o and -1.3%o (Feranec, 2003).

In addition to the utility of 613C ValUeS, Valuable dietary and environmental

information can also be attained from the 6 O0 values of structural carbonate and

phosphate in enamel. Several studies have determined that the 6 O0 of a mammal's body

water is directly correlated to the 6 O0 of ingested water from drinking water and food,

such as plants (Luz, Kolodny, and Horowitz, 1984; Luz and Kolodny, 1985; Bryant and

Froelich, 1995; Bryant, Froelich, Showers, and Genna, 1996a; Kohn, 1996). Furthermore,









these 618O values are recorded in the structural carbonate and phosphate of mammalian

tooth enamel, which mineralizes in isotopic equilibrium with body water (Longinelli,

1984; Luz et al., 1984). This conclusion has been corroborated by the calculation of a

consistent fractionation factor for oxygen between body water and structural carbonate in

modern equids (Bryant, Koch, Froelich, Showers, and Genna, 1996). Therefore, the 618O

values of mammals can be used to determine the 618O values of their water source.

However, it must first be determined whether that particular mammal obtains most of its

body water from plants or drinking water.

For obligate drinkers, tooth enamel can reflect the 618O values of meteoric water.

The 618O values of precipitation are controlled by temperature (Dansgaard, 1964).

Typically, this link causes the 618O values of meteoric water to be enriched during

periods of warm weather and depleted during periods of cool weather (McCrea, 1950;

Bryant et al., 1996a). The 618O values of meteoric water can therefore be used to interpret

seasonality. As mentioned previously, the 618O values of water sources are reflected in

the carbonate and phosphate of mammalian tooth enamel (Longinelli, 1984; Luz et al.,

1984). However, the metabolic rate of the mammal can influence the 618O values

recorded in the enamel (Bryant and Froelich, 1995; Kohn, 1996; Kohn, Schoeninger, and

Valley, 1998; Zhow and Zheng, 2002). This poses a problem for using small mammals

as environmental indicators, but Bryant and Froelich (1995) note that "because the

proportion of oxygen taken up as liquid water increases while the food requirement

decreases, the proportion of surficial drinking water reflected in [68"O of body water] will

increase with increasing body size." The 618O of surface water will then be reflected in

the enamel phosphate and carbonate of large mammals that weigh more than 1 kg (Bryant









and Froelich, 1995). The use of 618O values from tooth enamel as environmental

indicators has been extended to fossils, where the variation of 68"O values of enamel

phosphate along serially sampled teeth from Miocene horses (Bryant et al., 1996a) and

Holocene bison and sheep (Gadbury, Todd, Jahren, and Amundson, 2000) has been

determined to reflect seasonality. Similar studies have been conducted using the

structural carbonate in tooth enamel (Cerling and Sharp, 1996; Higgins and MacFadden,

2004; MacFadden and Higgins, 2004). Therefore, along the serially sampled tooth of an

obligate drinker, more positive (or enriched) 68xO values will indicate summer and more

negative (or depleted) values will indicate winter (Fricke and O'Neil, 1996; Feranec and

MacFadden, 2000).

For herbivores that are not obligate drinkers, the 618O of structural carbonate in

fossil teeth reflects the 618O of the water in consumed leaves (Longinelli, 1984; Bryant,

Froehlich, Showers, and Genna, 1996; Koch, 1998). The 618O of water in plants is

influenced by temperature, and humidity (Dongman, Nurnberg, Fiirstel, and Wagener,

1974; Epstein, Thompson, and Yapp, 1977; Sternberg, Mulkey, and Wright, 1989). Due

to this relationship, evapotranspiration causes leaves in forest canopies and dry, open

habitats to have higher 618O values than ground-level leaves in cool, humid forests

(Fiirstel, 1978; Kohn, Schoeninger, and Valley, 1996; Cerling, Harris, Ambrose, Leakey,

and Solounias, 1997a). These values can be enriched by more than 20%o compared to the

68xO of local precipitation (Fiirstel, 1978; Kohn et al., 1996). For non-obligate drinkers,

the 618O of structural carbonate can yield some general information about the mammal's

habitat ("e.g.", arid, open areas versus cool forests), but it does not accurately reflect

seasonality.









Materials and Methods

The assemblage of eight ungulates analyzed ranges from expected browsers

(brachydont dentitions found in the unidentified artiodactyl, oreodont, one rhinocerotid,

and one equid) to expected mixed feeders/grazers (mesodont to hypsodont dentitions

found in three equids and one rhinocerotid). Due to the eruption order of teeth and the

weaning stage of mammals, the tooth positions most appropriate for a post-nursing diet

analysis are the third premolar (P3), fourth premolar (P4), and third molar (M3) (Bryant

et al., 1996a; Fricke and O'Neil, 1996; Hoppe, Stover, Pascoe, and Amundson, 2004).

Other teeth were analyzed for taxa that lacked any positively identified P3 s, P4s, or M3 s.

These taxa include Anchitherium clarencei, Teleocera~s, and Aphelops. In all, twenty-four

teeth were selected for bulk stable carbon and oxygen isotope analysis of enamel

carbonate (Table 5-1). Bulk samples, taken along the entire height of the tooth, yield an

average stable isotopic ratio for the time during which the enamel mineralized. Six

specimens, two from three different taxa, were also chosen for serial sampling to obtain

isotopic ratios with finer resolution. The taxa chosen were: Aphelops sp., the brachydont,

long-limbed rhinocerotid expected to be an open-country cursorial browser; M~erychippus

primus, a hypsodont horse presumed to be a mixed feeder; and Acritohippus isonesus, the

most hypsodont taxon from the assemblage that is expected to be a grazing horse.

Serial samples of bioapatite were taken from 6 teeth at 5-millimeter intervals along

the length of each tooth. Serial stable isotope analyses were conducted in order to analyze

the variation of diet for an individual. Since a tooth mineralizes from the crown to the

base over the course of a few months to two years (Hillson, 1986), serial samples reveal a

dietary interpretation from a smaller time interval than a bulk sample. However, the

isotopic signals are masked due to the slightly non-perpendicular mineralization of tooth









enamel (Passey and Cerling, 2002). Despite this effect, the serial samples still yield an

isotopic ratio that is averaged over shorter time intervals than a bulk sample and allows

some variation to be discerned (MacFadden and Higgins, 2004). For the purposes of this

study, it is important to show any C4 dietary influences throughout the mineralization

stage of the animal.

The sampling and preparation procedures for stable isotope analysis are comprised

of two main components: 1) physical sampling and 2) chemical processing. The physical

sampling consists of the actual removal of enamel for analysis and the chemical

processing is the procedural treatment of the enamel to remove organic compounds and

all other contaminants that will affect the stable isotope signature. The physical sampling

begins by identifying any enamel flakes on the tooth that appear pliable. The surface of

the flake is cleaned using brushes, and then removed. A drill is then used to remove any

dentine remaining on the inside surface of the flake. It is then ground in a clean mortar

and pestle, and the enamel powder is placed in a labeled microcentrifuge vial. If there are

no flakes apparent, then a part of the tooth must be drilled, preferably where the enamel is

thick. The surface is prepared by cleaning it with carbide dental drill bits and brushes.

All the cementum and soil must be removed from the tooth to avoid contaminating the

sample. Once the surface is cleaned, a Foredom drill is used at low RPM' s to remove

approximately 5 milligrams of pristine enamel. The drill operator must be careful not

drill into the dentine, as dentine has a different 813C Value fTOm enamel and will

contaminate the sample. Bulk samples were taken along the entire height of the tooth,

while serial samples were taken at 5-millimeter increments starting at the base of the










tooth. All the enamel powder is collected on weighing paper and placed into a labeled

microcentrifuge vial.

The first step in the chemical treatment of the enamel samples is to remove all

organic material that might affect the carbon isotope ratio. To do this, 1 mL of 30%

H202 is added to each sample. Then, the vials are closed and shaken on a Thermolyne

Type 16700 Mixer in order to thoroughly mix the enamel powder with the H202. The

samples are then placed, with the lids off, in a reaction cabinet overnight. After

approximately 24 hours, some of the samples may still be reacting with the H202,

indicating the presence of abundant organic residues. The samples are all treated a

second time with H202 to remove these organic materials.

After the second H202 treatment, the samples are centrifuged and the H202 is

removed. One milliliter of distilled water is added to each vial and then mixed. The

samples are centrifuged, and the water is removed using a pipetter. This rinsing step is

repeated two more times. After the third rinse, 1 mL of 0. 1 M acetic acid is added to the

vials to remove carbonates from the samples. The samples are shaken and left in the

reaction cabinet overnight. The samples are not allowed to react with the acetic acid for

more than 24 hours, since it has been shown that prolonged exposure to acetic acid can

affect the carbon isotope signatures (Lee-Thorpe, Sealy, and van der Merwe, 1989;

Vennemann, Hegner, Cliff, and Benz, 2001).

The next day, the samples are centrifuged and the acetic acid is removed. Distilled

water is used to rinse the samples three more times. After the rinses, 95% methanol is

added to each sample to remove water. Again, the samples are shaken to mix the









methanol with the enamel, and then the methanol is removed. Finally, the samples are

placed in the reaction cabinet to dry overnight.

After the samples have dried, they are analyzed using a VG Prism mass

spectrometer at the Department of Geological Sciences at the University of Florida.

Approximately 1 mg of each sample is placed in a small sample boat and loaded into the

mass spectrometer, accompanied by standards. The bulk samples are standardized to

either the MEme (MacFadden Elephantus maximus enamel, 613C = -10.43%o) or the

NBS-19 (613C = +1.95%o; Coplen, 1996) standard to ensure the precision of the results

and the calibration of the mass spectrometer. All of the serial samples are calibrated to

the NBS-19 standard. All of the measured isotopic values are then calibrated to the

universal V-PDB (Vienna Pee Dee Belemnite). The values are presented in standard

6-notation: 613C Of 6180 = [(Rsample RV-PDB) 1] x 1000, where Rsample IS the measured

13 /12C Of 180/160 ratio of the sample. The analytical precision of samples run with the

MEme standard is f0.05 and f0.07 for 613C and 68 ", respectively. The analytical

precision of samples run with the NBS-19 standard is f0.09 and f0.18 for 613C and 68 ",

respectively. The analytical precision is measured by calculating one standard deviation

of the corrected 813C and 68 values of the standards.

Results

The bulk 813C ValUeS for all the sampled specimens range from -11.39%o to -8.30%o

(Table 5-2, Table 5-3, Figure 5-2). The most positive mean bulk 813C value belongs to

Aphelops sp. and the most negative belongs to Teleocera~s sp., although Teleocera~s has a

sample size of only one. The bulk 68 O values for all the sampled specimens range from

-2.15%o to 2.71%o (Table 5-3, Figure 5-2).









Three taxa were selected for serial sampling: one expected browser with

brachydont dentition (Aphelops sp.) and two expected grazing/mixed feeding horses with

hypsodont dentitions (M\~erychippus primus and Acritohippus isonesus). Individual serial

stable isotope values are presented in Appendix B. The serial stable isotope samples for

the first specimen of Aphelops (UF 1 16827) range from -8.37%o to 11.72%o for carbon

and from -1.99%o to -0.31%o for oxygen. (Table 5-3, Figures 5-3 and 5-4). The second

specimen (UF 104227) has a narrower range of -9.76%o to -10.73%o for carbon and a

much wider and more positive range of 0.71%o to 3.46%o for oxygen (Table 5-3, Figures

5-3 and 5-4). For M\~erychippus primus, the serial 613C ValUeS range from -9.26%o to

-10.54%o (UF 221419) and from -9.39%o to -9.72%o (UF 221427) and the serial 6 O0

values range from 0. 15%o to 1.99%o (UF 221419) and from 1.12%o to 2.83%o (UF

221427) (Table 5-3, Figures 5-5 and 5-6). Acritohippus isonesus exhibits serial 813C

ranges of -9.92%o to -10.66%o (UF 221407) and -10.33%o to -11.96%o (UF 217590) as

well as serial 6 O0 ranges of 0.25%o to 2.56%o (UF 221407) and 0.62%o to 2.37%o (UF

217590) (Table 5-3, Figures 5-7 and 5-8).














Atmosphere CO,


-1 9 5%


Figure 5-1. Schematic of isotopic fractionation between atmospheric carbon and C3
plants, as well as fractionation between C3 plants and ruminant herbivores.
613C ValUeS are listed in parentheses. The average 613C Value foT C3 plants is
approximately -27.1%o and the average 613C Value foT C3-COnSuming
ruminants is approximately -13%o. The average isotopic fractionation between
atmospheric carbon and C3 plants is a depletion of about -19.5%o. The isotopic
fractionation between plants and ruminants is an enrichment of approximately
14.1l%o. (Modified with permission from Koch et al., 1992)


C3 vegetation
(-27.1%.0)










Table 5-1. List of the 24 specimens analyzed for stable carbon and oxygen isotope
analysis. Specimens are representatives of the Willacoochee Creek Fauna
from the early Barstovian (middle Miocene) Dogtown Member of the Torreya
Formation. Abbreviations: UF ID = catalogue number in the Florida Museum
of Natural History collections, ELC = Englehard La Camelia Mine, LC2 = La
Camelia 2, and MGF = Milwhite Gunn Farm Mine.

UJF ID Taxon Crown Height Tooth Site
221429 Teleoceras sp. Brachydont R. I ELC
104227 Aphelops sp. Brachydont Tooth fragment MGF
116827 Aphelops sp. Brachydont R. Mx fragment ELC
217565 cf. Aphelops Brachydont L. Px LC2
114723 Anchitherium clarencei Brachydont L. P2 ELC
221402 Anchitherium clarencei Brachydont R. M1 ELC
217590 Acritohippus isonesus Hypsodont L. P4 LC2
217562 Acritohippus isonesus Hypsodont R. M3 LC2
221405 Acritohippus isonesus Hypsodont L. M3 ELC
221407 cf. Acritohippus isonesus Hypsodont R. P3/4 ELC
114721 Merychippus gunteri Mesodont R. M3 ELC
116829 Merychippus gunteri Mesodont L. P3/4 ELC
221416 Merychippus gunteri Mesodont L. P3/4 ELC
221408 Merychippus gunteri Mesodont L. M3 ELC
114976 Merychippus primus Mesodont R. P3/4 ELC
104208 Merychippus primus Mesodont L. P3/4 MGF
221415 Merychippus primus Mesodont R. P3 ELC
221419 Merychippus primus Mesodont L. P4 ELC
221426 Merychippus primus Mesodont R. M3 ELC
221427 Merychippus primus Mesodont R. M3 ELC
221428 Merychippus primus Mesodont R. M3 ELC
221418 Merychippus primus Mesodont R. M3 ELC
116823 Ticholeptus hypsodus Brachydont R. M3 ELC
221434 Artiodactyla Brachydont R. M? ELC










Table 5-2. Bulk stable carbon and oxygen isotope values for Willacoochee Creek Fauna.
Abbreviations: UF ID = catalogue number in Florida Museum of Natural
History collections, Unident. = unidentified tooth position, ELC = Englehard
La Camelia Mine, MGF = Milwhite Gunn Farm Mine, and LC2 = La Camelia
2 Mine.

UJF ID Taxon 613C ooo) 6180 (%o) Tooth Site
221429 Teleoceras sp. -11.39 -0.41 R. I ELC
104227 Aphelops sp. -9.48 1.01 Unident. MGF
116827 Aphelops sp. -8.72 -2.15 R. Mx ELC
217565 cf. Aphelops -10.23 0.38 L. Px LC2
114723 Anchitherium clarencei -8.90 2.32 L. P2 ELC
221402 Anchitherium clarencei -10.23 1.45 R. M1 ELC
217590 Acritohippus isonesus -10.87 2.03 L. P4 LC2
217562 Acritohippus isonesus -11.00 -0.35 R. M3 LC2
221405 Acritohippus isonesus -9.67 1.95 L. M3 ELC
221407 cf. Acritohippus isonesus -10.16 1.02 R. P3/4 ELC
114721 Merychippus gunteri -11.09 -0.65 R. M3 ELC
116829 Merychippus gunteri -8.30 -0.16 L. P3/4 ELC
221416 Merychippus gunteri -9.72 1.86 L. P3/4 ELC
221408 Merychippus gunteri -11.19 0.67 L. M3 ELC
114976 Merychippus primus -8.78 1.36 R. P3/4 ELC
104208 Merychippus primus -9.54 -0.82 L. P3/4 MGF
221415 Merychippus primus -8.79 2.10 R. P3 ELC
221419 Merychippus primus -10.00 0.85 L. P4 ELC
221426 Merychippus primus -9.76 1.14 R. M3 ELC
221427 Merychippus primus -8.70 1.03 R. M3 ELC
221428 Merychippus primus -9.73 0.45 R. M3 ELC
221418 Merychippus primus -9.50 0.97 R. M3 ELC
116823 Ticholeptus hypsodus -9.83 0.33 R. M3 ELC
221434 Artiodactyla -10.87 0.66 R. M? ELC










Table 5-3. Descriptive statistics of the 613C and 68 values for 8 herbivores from the
Willacoochee Creek Fauna. Abbreviations: Unident. = unidentified, N =
sample size, SD = standard deviation.


Bulk Sampling
Taxon N 813 o/oo) 6180 (%o)
Mean SD Range Mean SD Range
Anchitherium clarencei 2 -9.57 0.94 -10.23 to -8.90 1.89 0.94 1.45 to 2.32
Merychippus primus 8 -9.35 0.51 -10.39 to -8.70 0.89 0.84 -0.82 to 2.10
Merychippus gunteri 4 -10.08 1.36 -11.19 to -8.30 0.43 1.10 -0.65 to 1.86
Acritohippus isonesus 5 -10.43 0.62 -11.00 to -9.67 1.16 1.11 -0.35 to 2.03
Teleoceras sp. 1 -11.40 ---0.41
Aphelops sp. 3 -9.48 0.76 -10.23 to -8.72 -0.25 1.67 -2.15 to 1.01
Ticholeptus hypsodus 1 -9.83 --0.33
Unident. artiodactyl 1 -10.87 --0.66

Serial Sampling
Taxon N 813 o/oo) 6180 (%o)
Mean SD Range Mean Range
Aphelops sp. 19 -10.52 0.82 -10.23 to -8.72 0.06 -1.99 to 3.46
Merychippus primus 9 -9.67 0.43 -10.39 to -8.70 1.66 0.15 to 2.90
Acritohippus isonesus 12 -10.66 0.65 -11.19 to -8.30 1.51 0.25 to 2.56
























































Figure 5-2. Plot of bulk 813C VS. 6180 values for the 8 herbivores from the Willacoochee Creek Fauna. Note that all the herbivores
bear bulk 813C ValUeS below -8.30%o and most specimens cluster between -9.50%o and -10.50%o.


2.50-

2.00-

1.50-

1.00-

0.50-




-0.50-

-1.00-

-1.50-

-2.00-

-2.50 -
-11.50


O


-11.00


-10.50


-10.0 0


-9.50


-9.0 0


-8.0 0


6 C (%9)~


+ Artiodactyla Acritohippus isonesus + Merychippus primus A Merychippus gunteri

SAnchitherium clarencei + Aphelops x TeloceraIs


cl Ticholeptus hypsoclus
















-8.00


-8.50

-9.00


-9.50

-10.00


-10.50

-11.00




-12.00


0 5 10 15 20 25 30 35 40 45 50
Position along tooth (mm)



Figure 5-3. F13C ValUeS for serial samples of two Aphelops specimens. Note that all the
values are lower than -8.37 %o. Position along tooth refers to the distance from
the base of the tooth.







3.50-



2.50-



1.50-


S0 If

0.50



-0.50-


-1.50 -o--UF116827 -m-UF104227


-2.50
0 5 10 15 20 25 30 35 40 45 50
Position Along Tooth (mm)



Figure 5-4. 6 O0 values for serial samples of two Aphelops specimens. Note that both

specimens exhibit variation outside of the range of error. Position along tooth
refers to the distance from the base of the tooth.












-9.00


-9.25


-9.50




" -10.00


-10.25


-10.50


-10.75


-*- UF 221419 -m- UF 221427


Position along tooth (mm)


Figure 5-5. 613C ValUeS for serial samples of two M~erychippus primus specimens. Note
that all the values are lower than -9.26%o. Position along tooth refers to the
distance from the base of the tooth.


O 5 10 15 20
Position along tooth (mm)


Figure 5-6. 618O values for serial samples of two M~erychippus primus specimens. Note
that both specimens exhibit variation outside of the range of error. Position

along tooth refers to the distance from the base of the tooth.












9.75

-10.00


-10.25

-10.50

-10.75




-11.25

-11.50

-11.75


-12.00

-12.25


-4-UF 221407 -m-UF 217590


10 15 20
Position along tooth (mm)


Figure 5-7. 613C ValUeS for serial samples of two Acriohippus isonesus specimens. Note
that all the values are lower than -9.92%o. Position along tooth refers to the
distance from the base of the tooth.


3.00




2.50




2.00








1.00




0.50




0.00


5 10 15 20
Position along tooth (mm)


Figure 5-8. 618O values for serial sampling of two Acritohippus isonesus specimens.
Note that both specimens exhibit variation outside of the range of error.

Position along tooth refers to the distance from the base of the tooth.















CHAPTER 6
DISCUSSION

Of the eight taxa analyzed from the Willacoochee Creek Fauna (WCF), three are

expected to yield significant proportions of browse in their diets: Anchitherium clarencei,

Ticholeptus hypsodus, and Aphelops. A. clarencei is a three-toed horse with low-crowned

cheek teeth and stocky limbs suggestive of a browse diet in a woodland habitat (Janis et

al., 2002). The only positively identified artiodactyl from the WCF, T. hypsodus, has a

mesodont dentition and is expected to be a mixed feeder (Lander, 1998). Aphelops is a

hornless, brachydont aceratherine rhino with long limbs suggestive of a cursorial habit

(Matthew, 1932; Janis, 1982). Aphelops is traditionally described as an open-country

browser, with the extant black rhino (Diceros bicornis) cited as a modern analog

(Matthew, 1932). Furthermore, Janis (1982) described all aceratherine rhinos as browsers

within woodland savannas. There has been some variance on the dietary classification of

Aphelops. Webb (1983) recognized Aphelops and Teleocera~s as grazers from the

'Clarendonian Chronofauna,' the succession of Barstovian-Clarendonian grazers.

However, stable isotopic analyses ofAphelops specimens from multiple Florida localities

(ranging from 9.5 to 4.5 Ma), combined with crown-height data, suggest that Aphelops

was eating C3 browse material before and after the ~7 Ma spread of C4 graSSCS

(MacFadden, 1998). The WCF Aphelops specimens are approximately 6 million years

older than the previously analyzed specimens, but the dental and postcranial

morphologies still suggest a diet of C3 browse.









Teleocera~s is a moderately hypsodont teleoceratine rhino with short limbs. It has

been traditionally interpreted as semi-aquatic grazer, comparable to the extant

hippopotamus, Hippopotamust~~~~~tttt~~~~ amphibious (Scott, 1937; Voorhies, 1981; Webb, 1983;

Prothero, 1992). Matthew (1932) rej ected the hypothesis of a semi-aquatic habitat for

Teleocera~s, and instead suggested that the rhino grazed on grassy plains. Voorhies and

Thomasson (1979) determined that Teleocera~s was a grazer, based on the presence of

grass anthoecia in the oral and body cavities of specimens from the Ashfall Fossil Beds in

Nebraska (10 Ma). They were, however, unable to determine whether that grass

originated from mesic or lacustrine environments. Recent isotopic evidence, however,

has revealed that: 1) Teleocera~s was, based on 68 values, not primarily aquatic; and 2)

Teleocera~s was a mixed feeder, consuming significant portions of C3 graSs prior to the 7

Ma spread of C4 graSses and then shifting to a diet of C4 graSses after 7 Ma (MacFadden,

1998). This interpretation likens Teleocera~s to the extant white rhino (Ceratotheriunt

sinsun), a grazer (MacFadden, 1998). Based on this interpretation of Teleocera~s, the

specimens from the WCF would be expected to have 613C Signatures indicative of a

mixed diet, possibly composed of C3 graSSCS.

The remaining equids from the WCF are all hypsodont three-toed horses. The

hypsodont teeth of 2erychippus primus and M~erychippus gunteri suggest a

grazing/mixed diet for these equids. Janis (1988) points out that, despite fairly hypsodont

cheek teeth, the M~erychippus dentition is more similar to that of extant mixed feeders

than to grazers. Whether M~erychippus was a grazer or mixed feeder, the tooth

morphology suggests that there is at least some grazing component to the animal's diet.









Acritohippus isonesus, the most hypsodont taxon of the WCF, would be expected to be a

grazer.

Based on average bulk stable carbon isotope values, all eight taxa from the WCF

fell within the range of a C3-dominated diet, between -21%o and -8%o (Cerling and

Harris, 1999). Additionally, only one sample had a 613C Value more positive than -8.7%o

(a M~erychippus gunteri specimen had a value of -8.30O%o), indicating that nearly the entire

WCF community was consuming strictly C3 plants, according to the pre-industrial ranges

of Feranec (2003). Even the most positive value was still more negative than -7.9%o,

indicating that the animal was eating less than 10% C4 graSS.

However, atmospheric 613C ValUeS during the middle Miocene were considerably

higher than during the pre-industrial Holocene (Vincent and Berger, 1985). During the

Monterey Excursion, from 16.5 Ma to 13.5 Ma, 613C ValUeS of benthic foraminifera were

as high as +2.2%o, indicative of higher atmospheric 613C (Zachos et al., 2001). The higher

atmospheric 613C WOuld raise the 613C Of plants, slightly raising the 613C Of the enamel of

mammals that consume the plants. This increase would be no greater than about 1%o.

Taking this enrichment into account, the 613C Signatures of all the samples are well

within a pure C3 diet. This suggests that each ungulate was either grazing on C3 graSSCS Of

browsing, and not consuming any significant amounts of C4 graSs. The serial sampling of

Aphelops sp., M~erychippusprimus, and Acritohippus isonesus, also reveal no significant

C4 fluctuations in diet at any point during the mineralization of the enamel. For both

Aphelops sp. and M\~erychippus primus, the most enriched serial sample was not greater

than -8.7%o, indicating a pure C3 diet. Once again, when the higher atmospheric 613C iS

considered, the serial samples fall well within the range of a pure C3 diet.










The stable carbon isotope analyses support the browser interpretations based on

dental morphologies for A. clarencei, T. hypsodus, and Aphelops. Conversely, the

dentitions and lack of a C4 Signal for Teleoceras and the three hypsodont equids suggest

that they were consuming C3 graSses. Unfortunately, the sample sizes ofM. primus, M~

gunteri, and Teleocera~s are inadequate for further investigation of grass consumption

("e.g.", microwear or mesowear analyses). Likewise, the sample sizes of the suspected

browsers are also insufficient for direct confirmation of a browse-dominated diet. A.

isonesus, however, can be assessed for evidence of a grass diet through microwear

analy si s.

While conducting the microwear analyses, there was some doubt as to whether

two of the A. isonesus molars were M2s. However, since the parametric and

nonparametric statistical tests found no significant differences between the microwear

indices (MI) of each A. isonesus specimen, they are accepted here as all being M2 teeth.

The average microwear index (MI) for A. isonesus is 1.97, well above the 1.5 threshold

for grazers (MacFadden et al., 1999). The MI for N. trampa~sense is 1.98, which is also

significantly higher than 1.5. This supports the mesowear analysis, which classifies N.

trampasenser~rtrtrtrt~t~t~ as a grazer. The MI of A. isonesus is not statistically different from that of

N. trampasense.~rtrtrtrt~t~t~ The relatively high MI of A. isonesus, coupled with the lack of a

significant difference to the MI from the grazing N. trampa~sense, suggests that A.

isonesus was also dominantly a grazer, with no significant browse component. The 613C

data and microwear index indicate that A. isonesus was a C3 grazer (Figure 6-1). This

conclusion is supported by the scratch morphology. The quantified scratches in extant

grazers have indicated that a prevalence of fine scratches are observed in consumers of C3









grasses, while coarse scratches dominate the enamel wear of C4 graZeTS (Solounias and

Semprebon, 2002). For each sample ofA. isonesus, fine scratches composed at least 84%

of the total number of scratches.

Further paleoecological interpretations can be made from the bulk and serial 613C

values of the WCF. In closed canopy forests, CO2 becomes trapped near the forest floor,

elevating the CO2 COncentration near the forest floor and in turn depleting the 613C Of that

air which, in turn, results in the depletion of 13C in plant tissues (Medina and Minchin,

1980; Medina, Montes, Cuevas, and Rokzandic, 1986; van der Merwe and Medina, 1989;

Cerling et al., 1997a). Further depletion of 13C in plant tissues results from the lack of

light reaching the forest floor, caused by the dense cover of the canopy (Medina and

Minchin, 1980; Medina et al., 1986; van der Merwe and Medina, 1989). These factors

cause the understory plants of a closed canopy forest to bear 613C ValUeS as low as -37%o,

a phenomenon known as the "Canopy Effect" (Medina and Minchin, 1980; Medina et al.,

1986; van der Merwe and Medina, 1989). The average 613C Value for these plants is -

30.9%o (Ehleringer, Field, Lin, and Kuo, 1986). Modern C3 plants that grow in open

areas and do not suffer from water stress exhibit a 813C range from -26 to -27%o (Cerling

et al., 1997a).

The range of bulk 813C ValUeS for all the sampled WCF is -11.39%o to -8.3%o,

which, considering analytical and fractionation error, indicates a diet that ranges in

isotopic composition from -25.49%o a 0.59%o to -22.40%o a 0.59%o. An adjustment for

the Monterey Excursion of -1%o changes the range to approximately -26.49%o a 0.59%o to

-23.40%o a 0.59%o. With this adjustment, all of the bulk samples have 613C ValUeS above

the maximum limit (-27%o) for the "Canopy Effect," although the error range of the









Teleocera~s sample extends down to -27.08%o. Even the two brachdyont taxa,

Anchitherium clarencei and Aphelops, have dietary bulk 813C ranges that preclude them

from eating ground-level browse in a closed canopy forest. The serial sampling also does

not support a closed-canopy dietary component. All the serial samples for M. primus,

Aphelops, and A. isonesus indicate diets that have 613C ValUeS above -27%o, except one A.

isonesus sample that yields a dietary value of -27.06%o. The error range of this sample,

along with the higher serial 613C ValUeS for this specimen, suggests that this specimen

was still not eating in a closed-canopy forest. The range of bulk and serial 613C ValUeS

for the WCF reveals that the mammals lived and ate in an open habitat, such as a

woodland savanna or grassland.

Paleoecological interpretations can also be made from the bulk 813C ValUeS of the

WCF. When C3 plants are suffering water stress, they become enriched in 13C (Ehleringer

et al., 1986; Ehleringer and Cooper, 1988; Ehleringer, 1991). During episodes of water

stress, plants close their stomata to conserve water, consequently reducing CO2 intake

and enriching the 613C Of C3 plant tissues as high as -22%o (Ehleringer et al., 1986;

Ehleringer and Cooper, 1988; Ehleringer, 1991). As mentioned above, the calibrated

isotopic range of the WCF diet is -25.49%o a 0.59%o to -22.40%o a 0.59%o. An adjustment

for the Monterey Excursion of -1%o changes the range to approximately -26.49%o &

0.59%o to -23.40%o f 0.59%o. This range suggests that the WCF were feeding off of C3

plants in open areas that periodically experienced water stress. This interpretation is

supported by the serial sampling, which reveals dietary ranges of -24.36%o a 0.59%o to

-25.64%o a 0.59%o for two serially sampled M. primus specimens and -25.02%o a 0.59%o

to -27.06%o a 0.59%o for the two serially sampled A. isonesus specimens. The serially









sampled specimens of Aphelops also support an interpreted diet of water-stressed C3

plants, with significantly variant dietary ranges of -23.47%o a 0.59%o to -26.82%o &

0.59%o. The stable carbon isotopic evidence suggests that the WCF were consuming

water-stressed plants in open arid and seasonal environment, such as open-country plains.

Interpretations about local seasonality can be made from the serial 6 O0 values

from the structural carbonate in the enamel of the WCF. Assuming that equids from the

middle Miocene were obligate drinkers like modern equids, the serial sampling should

reveal a noticeable curve in 68 O values. For M. primus, specimens UF221419 and

UJF221427 display trends that are nearly mirror images of one another. Enamel

mineralization, which begins at the crown, began during the winter for UF 221419, which

is evident from the low 6 O0 values at 15 and 10 mm from the base of the tooth. Enamel

mineralization, which takes about 1.5 to 2.8 years for cheek teeth in modern equids

(Bryant et al., 1996a), ended in the summer. Contrastingly, enamel mineralization for

UF221427 began in spring or early summer and was mostly completed by winter,

according to the high 68 O values from 20 to 5 mm from the tooth base that are within

error of one another. Although modern equid cheek teeth take a minimum of about 1.5

years to mineralize, it is possible for the teeth of 2erychippus primus to take less than a

year since the teeth are less high-crowned than modern equids. It should be noted that

each sample along the tooth bears a 6 O0 value that is time-averaged over a few months.

The other equid that was serially sampled, A. isonesus, reveals two distinct curves that

are also mirror images. UF221407 appears to have begun enamel mineralization towards

the end of summer or fall and continued through the entire winter and into the next









summer. UF217590 began enamel mineralization in early summer or spring, in the

winter.

Modern rhinocerotids are obligate drinkers (Clauss et al., 2005). Assuming that

Aphelops is also an obligate drinker, the 618O values of the enamel carbonate should

reflect any seasonal variation. UF 104227 displays considerable variation. Tooth

formation began during the 618O lows of winter. There are two summer peaks and three

winter troughs, indicating that the Aphelops cheek tooth formed over roughly two years.

The 618O variation of UF 1 16827 is not as pronounced as UF 104227, but a curve outside

the error ranges is discernible. Tooth mineralization for UF 104227 began in a summer

peak. The curve features two summer peaks and two winter lows, suggesting that the

Aphelops molar took slightly more than a year to mineralize. The lower 618O values of

UF 1 16827 indicates that the tooth mineralized during a period of cooler temperatures

than UF 104227. Overall, the 618O variation in both Aphelops specimens supports the

interpretation seasonality in northern Florida during the middle Miocene.

The variation of 68"O values for the serially sampled specimens ofM.~ primus, A .

isonesus, and Aphelops suggests that the WCF experienced significant seasonality. This

stable oxygen isotopic data supports the interpretations of periodic water-stress made

from the stable carbon isotopic data. The seasonality experienced by the WCF is typical

of the warming that took place in the middle Miocene.

The middle Miocene (early Barstovian) WCF represent an interesting transition in

the paleodiets of Floridian mammals. The mesodont equid Parahippus leonensis can be

found at the early Miocene (Hemingfordian) Thomas Farm locality, from about 19 to 18

Ma (Hulbert and MacFadden, 1991). The rate of wear for P. leonensis cheek teeth is









about half of wear rate of grazing equids, indicating a mixed diet of grass and browse

(Hulbert, 1984). This interpretation has been supported by mesowear analyses (Hoffman,

unpublished). This suggests that grasses, either C3 Of C4, eXiSted in central Florida as far

back as 19 Ma, but the mesodont equids at were still consuming significant amounts of

browse. Only hypsodont equids, like Acritohippus isonesus, were capable of exploiting

the more abrasive grasses. Thomas Farm also yields the brachydont equids Anchitherium

and Archaeohippus. A diminuitive presence of grasses would explain the lack of

hypsodont taxa at the Thomas Farm site. It was only after C3 graSses became more

abundant, by 15.8 Ma in northern Florida, that equids radiated into hypsodont lineages.

Mesowear analyses revealed grazing diets for all five of the hypsodont equids from

the last 10 million years. Coupled with previous isotopic data (Table 6-1), it is possible to

trace the existence of C3 graSses over the last 10 million years in Florida. All three horses

from the Love Site (Neohipparion trampasense,~rtrtrtrt~t~t~ Cormohipparion plicatile, and

Cormohipparion ingenuum) have 613C ValUeS indicative of a C3-dominated diet.

Furthermore, the most positive 613C Value Of these samples is -10.8%o, well below -8.7%o.

This indicates that the diets of these horses consisted purely of C3 plants. Since the

mesowear analyses indicate that these taxa were primarily grazers, they must have been

feeding on C3 graSses. The 613C ValUeS from enamel indicate a range of -26.7%o to

-24.9%o for the consumed plants. This suggests that the equids were eating water-stressed

C3 graSses in seasonal, open habitat. This interpretation compares favorably with other

studies. The population dynamics of N. trampasenser~rtrtrtrt~t~t~ from the Love Site reveal a high rate

of tooth wear, comparable to the modern zebra Equus burchelli, which indicates a highly

abrasive grass-dominated diet (Hulbert, 1982). The presence of discrete age classes at the









site suggests that the area was a wooded grassland savanna with seasonal rains that

controlled the migratory and birthing patterns (Hulbert, 1982). N. trampasenser~rtrtrtrt~t~t~ migrated

away from the Love site during the wet season to give birth, then returned during the dry

season (Hulbert, 1982). This interpretation is supported by the range of 613C ValUeS,

which suggest that the equids at the Love Site were consuming water-stressed grasses.

The next site, the Upper Bone Valley Formation, features specimens ofl~annippus

aztecus that represent the 4.5 Ma level. The three 613C ValUeS for N. aztecus indicate a

diet composed of both C3 and C4 plant material (Table 6-1). Combined with the

mesowear grazer classification, N. aztecus can be interpreted as an opportunistic grazer,

feeding on both C3 and C4 graSses and possibly some browse. This level is dated after the

global shift in carbon biomass, when C4 graSses became dominant. However, the N.

aztecus specimens consist of an Ml, an M2, and an M1/2. First molars are completely

mineralized during the weaning process, suggesting that the isotopic compositions of

Mis are influenced by the mother's milk (Bryant et al., 1996a; Fricke and O'Neil, 1996;

Hoppe et al., 2004). Second molars are not completely mineralized until after the

weaning process ends, but they can still reflect the isotopic composition of the nursing

diet (Bryant et al., 1996a; Fricke and O'Neil, 1996; Hoppe et al., 2004). The M2 and

M1/2 613C ValUeS, therefore, might be skewed.

A study conducted on 6 sympatric horses from Upper Bone Valley Formation

concluded that, as recently as 5 million years ago, Cq tropical grasses in Florida coexisted

with C3 graSses. Using microwear, this study showed that Nannippus aztecus, along with

the sympatric late Hemphillian horse Pseudhipparion simpsoni, consumed both C3 and C4

grasses (MacFadden et al., 1999). This study substantiates the interpretation of









NNNNNNNNNNNNNNNNNNNNanipu aztecus as a C3 C4 grazer. Furthermore, older N. aztecus specimens from the 7

Ma Moss Acres Racetrack site (Table 6-1) have 613C ValUeS of -7.9%o and -5.3%o. These

values indicate a mixed diet of C3 and C4 plants. Mesowear analyses could not be

conducted on this population because the population size was too small (<20). However,

if this population behaved similarly to the younger Upper Bone Valley Nannippus

populations ("i.e.", they were primarily grazing), then this population was likely

composed of C3 C4 graZeTS.

Finally, the Leisey Shell Pit represents the 1.5 Ma level. The specimens of Equus

"~le/Jy/" have 613C ValUeS that are more negative than -1.3%o, indicating a C4-dominated

diet with a minor C3 COmponent. Modern Equus is predominantly a grazer, but is known

to eat other locally available plants (Berger, 1986). The isotopic and mesowear data

suggests that, like modern Equus, Equus "leidyi" was a dominant C4 grazer at 1.5 Ma.

Previous work (MacFadden et al., 1999) as well as the mesowear analyses of

various Florida equid populations have shown that C3 graSses were present in Florida

from ~10 to ~5 Ma. In light of the microwear and isotopic data retrieved from the WCF,

it appears that the record of C3 graSses in northern Florida and southern Georgia extends

back to at least 15 million years ago. As evidenced by the consumption C3 graSses by a

hypsodont taxon, it is possible that C3 graSses forced the adaptation of hypsodonty in

ungulates.












I I II


2 3





0 17



" 11
09

0) 5


Pure C, IVixed Diet Pure C4













Q Acritohippus isonesus
HNeohipparion trampasense


|


-12 -11 -10


-9 -8 -7 -6 -5 -4 -3 -2 -1 0


8' C (V-PDB)



Figure 6-1. Plot of microwear index versus 613C ValUeS. The dashed line represents a
microwear index of 1.5, the boundary between a browser and a grazer
classification. Solid lines mark the boundaries between 'Pure C3 diet', 'Mixed
diet', 'Pure C4 diet" and transitional zones. 613C ValUeS below -8.7%o indicate
a pure C3 diet. Note that both Acritohippus isonesus and Neohipparion
trampasenser~rtrtrtrt~t~t~ have microwear indices above 1.5 and 813C ValUeS below -8.7%o,
suggesting diets composed purely of C3 graSSCS.











Table 6-1. Isotopic data for equids from 4 central Florida sites. Abbreviations: UF ID =
catalogue number in Florida Museum of Natural History collections.
(Modified woth permission from MacFadden and Cerling, 1996)


Taxon Site UF ID Material 613C (ooo


9.5 Ma Level, late Clarendonian, late Miocene
Love Bone Bed 32230 R. P3- 3
Love Bone Bed 32265 R. P2
Love Bone Bed 32265 R. P3
Love Bone Bed 32265 R. P4
Love Bone Bed 32265 R. M'
Love Bone Bed 60396 R. P2
Love Bone Bed 35979 R. P2


Neohipparion trampasense
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion ingenuum
Cormohipparion ingenuum


-11.6
-12.6
-12.5
-11.0
-12.0
-10.8
-10.8


7.0 Ma level,
Moss Acres
Moss Acres


"middle" Hemphillian, late Miocene
69933 R. M3
None R. P2


Nannippus aztecus
cf. Nannippus



Nannippus
Nannippus aztecus
Nannippus aztecus


4.5 Ma level, latest Hemphillian, early Pliocene
Upper Bone Valley None L. M
Upper Bone Valley 63633 L. M2
Upper Bone Valley 65796 R. M'


1.5 Ma level, early Irvingtonian, early Pleistocene
Equus "lleidyi"l Leisey 1A 80047 R. M3
Equus "leidvi Leisey 1A None R. P?















CHAPTER 7
CONCLUSIONS

Stable carbon isotope analyses of the Willacoochee Creek Fauna, the oldest

isotopically sampled taxa in Florida, provide no evidence for the presence of C4 graSSCS

in the diets of ungulates in northern Florida and southern Georgia at from 15.3 to 15.9

Ma. This suggests that C4 graSses were not present in the area at important time in

mammal evolution and, since they are not a significant dietary component, it is unlikely

that they were responsible for hypsodonty adaptations. Furthermore, the microwear of the

most hypsodont taxon from the WCF, Acritohippus isonesus, indicates a grazing diet.

Combined with the C3-COnSuming classification, based on 6 13C ValUeS from bioapatite,

the microwear suggests that Acritohippus isonesus ate C3 graSses. This substantiates the

presence of C3 graSses in the middle Miocene of northern Florida and supports Fox and

Koch's (2003) claim that C3 graSses were responsible for the hypsodonty adaptations.

Stable carbon and oxygen isotope values also indicate that the Willacoochee Creek Fauna

ate many water-stressed plants and lived in an open, arid, and seasonal environment, such

as open-country plains

Mesowear analyses and previously published isotope data reveal that the C3

grasses were the primary dietary component in some Floridian horses at ~9.5 Ma. Even

after the global carbon biomass shift at ~7 Ma, C3 graSses persisted in Florida and were

significant dietary components until at least ~4.5 Ma. By ~1.5 Ma, it appears that

abundance of C3 graSses finally subsided in Florida, where the dominant grazer (Equus

"le/Jyr )i~ was consuming mostly C4 graSs. This long reliance off of C3 graSses suggests









that C3 graSses were a driving mechanism for the appearance of hypsodonty in ungulates.

The combinations of mesowear and stable isotope analyses and microwear and stable

isotope analyses have proven to be valuable tools in assessing the origins of hypsodonty.

Future work will involve applying these combined methods to the northern Great Plains,

where there is a rich record of ungulate fossils.





UF ID Taxon Locality
62251 Neohipparion trampasense Love Site
25637 Neohipparion trampasense Love Site
27992 Neohipparion trampasense Love Site
32273 Neohipparion trampasense Love Site
32258 Neohipparion trampasense Love Site
27991 Neohipparion trampasense Love Site
32253 Neohipparion trampasense Love Site
53428 Neohipparion trampasense Love Site
53427 Neohipparion trampasense Love Site
32256 Neohipparion trampasense Love Site
32272 Neohipparion trampasense Love Site
32252 Neohipparion trampasense Love Site
53429 Neohipparion trampasense Love Site
53230 Neohipparion trampasense Love Site
53243 Neohipparion trampasense Love Site
53256 Neohipparion trampasense Love Site
53269 Neohipparion trampasense Love Site
53244 Neohipparion trampasense Love Site
53257 Neohipparion trampasense Love Site
53232 Neohipparion trampasense Love Site
53271 Neohipparion trampasense Love Site
53246 Neohipparion trampasense Love Site
53272 Neohipparion trampasense Love Site
53234 Neohipparion trampasense Love Site
53247 Neohipparion trampasense Love Site
53273 Neohipparion trampasense Love Site
53235 Neohipparion trampasense Love Site
53248 Neohipparion trampasense Love Site
53236 Neohipparion trampasense Love Site
53249 Neohipparion trampasense Love Site
53275 Neohipparion trampasense Love Site
53237 Neohipparion trampasense Love Site
53250 Neohipparion trampasense Love Site
53276 Neohipparion trampasense Love Site
53225 Neohipparion trampasense Love Site
53251 Neohipparion trampasense Love Site


Material
L. M1
L. M1
L. M2
L. M2
R. M2
L. M2
L. M2
L. M2
L. M1
L. M2
L. M2
L. M2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
R. M1/2
L. M1/2
L. M1/2
L. M1/2
R. M1/2
R. M1/2
R. M1/2
L. M1/2
L. M1/2
R. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
R. M1/2
L. M1/2
L. M1/2
R. M1/2
L. M1/2
L. M1/2


APPENDIX A
MESOWEAR VALUES LISTED BY SAMPLE


Table A-1. Abbreviations: UF ID = catalogue number in Florida Museum of Natural
History collections, CS = Cusp Shape, OR = Occlusal Relief, BVF = Bone
Valley Formation, Leisey = Leisey Shell Pit, B = Blunt, R = Round, S =
Sharp, H = High, L = Low.


CS OR











Table A-1.
UF ID
53277
53265
53278
53282
96934
53338
36289
27993
96933
32270
32260
32250
35891
32262
27316
32264
32283
32266
69811
53346
53377
53347
53348
53363
53379
53331
53349
53364
53351
53365
53352
53366
53336
53353
53367
53370
53339
53371
32300
32254
32296
53426
53396
53375
53391
53395
53394


Continued
Taxon
Neohipparion trampasense
Neohipparion trampasense
Neohipparion trampasense
Neohipparion trampasense
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion plicatile
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum


Locality
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site


Material
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M2
R. M2
R. M2
R. M2
L. M2
R. M1
L. M2
R. M2
L. M1
L. M2
R. M2
R. M2
L. M2
L. M2
R. M1
R. M1/2
L. M1/2
R. M1/2
R. M1/2
L. M1/2
L. M1/2
R. M1/2
R. M1/2
L. M1/2
R. M1/2
L. M1/2
R. M1/2
L. M1/2
R. M1/2
R. M1/2
L. M1/2
L. M1/2
R. M1/2
L. M1/2
L. M2
R. M2
L. M2
R. M1
R. M2
L. M1/2
R. M1/2
R. M1/2
R. M1/2











Table A-1.
UF ID
53390
53389
53383
53384
53385
62409
96377
62417
62391
62430
62398
62429
62395
62427
6700
57576
57576
212370
211769
208402
207957
203506
156921
156920
130079
124209
102613
102612
102611
100239
100241
93223
67981
63630
55933
55893
53953
47371
17252
208360
211787
211892
58296
63627
63633
63693
63964


Continued
Taxon
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Cormohipparion ingenuum
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus


Locality
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
Love Site
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF
BVF


Material
R. M1/2
R. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
R. M1/2
L. M1/2
R. M1/2
L. M1/2
R. M1/2
L. M1/2
R. M1/2
R. M2
L. M1
L. M2
R. M1
R. M1/2
R. M1/2
R. M1
R. M1/2
R. M2
R. M1
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1/2
R. M1
R. M1/2
R. M1
L. M1
L. M1
L. M1
L. M1
L. M1
L. M2
L. M1
L. M1











Table A-1.
UF ID
63967
17279
47362
80090
85523
85780
83800
85776
85772
85771
82642
84173
85708
85720
85710
85683
84172
85679
81636
85680
81797
85719
85727
85698
85730
85729
82079
85724
85689
85692


Continued
Taxon
Nannippus aztecus
Nannippus aztecus
Nannippus aztecus
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi"
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "
Equus "leidyi "


Locality
BVF
BVF
BVF
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey
Leisey


Material
L. M1
L. M1
L. M2
L. M1
L. M2
R. M1
R. M2
L. M1
R. M1
L. M1
L. M1
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2
L. M1/2


















APPENDIX B
SERIAL STABLE ISOTOPE VALUES


Table B-1. Abbreviations: ELC
Farm Mine, and LC2


Englehard La Camelia Mine, MGF = Milwhite Gunn
La Camelia 2 Mine.


Sample
Height

O nun

5 nun

10 nun

15 nun

20 nun

25 nun

30 nun

35 nun

40 nun

45 nun

50 nun
O nun
5 nun
10 nun
15 nun
20 nun
25 nun
30 nun
35 nun

0 nun

5 nun

10 nun

15 nun

0 nun

5 nun


813C oo)

-8.37

-9.98

-9.41

-9.91

-10.72

-10.94

-11.44

-11.35

-11.55

-11.28

-11.72
-9.76
-10.55
-10.40
-10.53
-10.54
-10.29
-10.39
-10.73

-9.26

-10.54

-10.19

-9.27

-9.39

-9.66


6180 (%o)


UJF ID

116827

116827

116827

116827

116827

116827

116827

116827

116827

116827

116827
104227
104227
104227
104227
104227
104227
104227
104227

221419

221419

221419

221419

221415

221415


Taxon

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.

Aphelops sp.
Aphelops sp.
Aphelops sp.
Aphelops sp.
Aphelops sp.
Aphelops sp.
Aphelops sp.
Aphelops sp.
Aphelops sp.

Merychippus primus

Merychippus primus

Merychippus primus

Merychippus primus

Merychippus primus

Merychippus primus


Tooth Site


R. Mx

R. Mx

R. Mx

R. Mx

R. Mx

R. Mx

R. Mx

R. Mx

R. Mx

R. Mx

R. Mx
Unident.
Unident.
Unident.
Unident.
Unident.
Unident.
Unident.
Unident.

L. P4

L. P4

L. P4

L. P4

R. P3

R. P3


-1.89

-1.95

-1.65

-1.26

-1.42

-1.55

-1.99

-1.19

-0.80

-0.90

-0.31
0.71
2.34
1.87
1.22
3.46
3.15
1.67
1.60

1.99

0.67

0.15

0.15

1.15

2.90


ELC

ELC

ELC

ELC

ELC

ELC

ELC

ELC

ELC

ELC

ELC
MGF
MGF
MGF
MGF
MGF
MGF
MGF
MGF

ELC

ELC

ELC

ELC

ELC

ELC











Table B-1. Continued


Sample
Height
10 mm

15 mm

20 mm

0 mm

5 mm

10 mm

15 mm

20 mm

25 mm

0 mm

5 mm

10 mm

15 mm

20 mm

25 mm


813 o/oo) 6180 (%o)


Tooth Site


UF ID

221415

221415

221415

221407

221407

221407

221407

221407

221407

217590

217590

217590

217590

217590

217590


Taxon

Merychippus primus

Merychippus primus

Merychippus primus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus

Acritohippus isonesus


-9.72

-9.49

-9.50

-9.94

-10.16

-10.34

-9.92

-10.63

-10.66

-10.52

-10.33

-10.70

-10.94

-11.78

-11.96


2.65

2.48

2.83

1.12

0.25

0.36

0.97

1.68

2.56

0.62

2.01

2.37

2.13

2.16

1.82


R. P

R. P3

R. P3

R. P3/4

R. P3/4

R. P3/4

R. P3/4

R. P3/4

R. P3/4

L. P4

L. P4

L. P4

L. P4

L. P4

L. P4


ELC

ELC

ELC

ELC

ELC

ELC

ELC

ELC

ELC

LC2

LC2

LC2

LC2

LC2

LC2
















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Full Text

PAGE 1

USING STABLE CARBON ISOTOPE, MICROWEAR, AND MESOWEAR ANALYSES TO DETERMINE THE PALEODIETS OF NEOGENE UNGULATES AND THE PRESENCE 0F C4 OR C3 GRASSES IN NORTH ERN AND CENTRAL FLORIDA By JONATHAN M. HOFFMAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

PAGE 2

Copyright 2006 by Jonathan M. Hoffman

PAGE 3

iii ACKNOWLEDGMENTS I would like to thank my advisor, Dr. J onathan Bloch for his guidance on this project. I would also like to thank my committee members: Dr. David Hodell, Dr. Richard Hulbert, and Dr. Andrew Zimmerma n. Their suggestions and advice are greatly appreciated. In addition to their helpful advice, Dr. Bloch, Dr. Hulbert, and Dr. Zimmerman all aided in collecting fossil samp les. I would like to thank Art Poyer and Jeremy Green for their help in collecting samples. I am especially appreciative of the Englehard Corporation and Dave Mihalik for allowing me to collect fossils from their mines and being incredibly helpful at those sites. I would like to thank Dr. Penny Higgins for her assistan ce in learning the sampling techniques for stable isotope analysis of fossil teeth and the chemical protocol for preparing those samples for analysis. I am greatly indebted to Dr. Jason Curtis for running my samples on the mass spectrometer and for all of his advice. My fellow graduate students aided me with discussion and advice. I am very appreciative of P.J. Moore, Warren Grice, Jane Gustavson, and Derrick Newkirk for listening and providing support. Fi nally, I would like to thank my family, who has always supported me and encouraged me to pursue my passions.

PAGE 4

iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES..........................................................................................................vii ABSTRACT.......................................................................................................................ix CHAPTER 1 INTRODUCTION........................................................................................................1 2 FIELD AREA AND FAUNA.....................................................................................17 3 MESOWEAR METHOD...........................................................................................29 Materials and Methods...............................................................................................31 Results........................................................................................................................ .32 4 MICROWEAR METHOD.........................................................................................40 Materials and Methods...............................................................................................41 Results........................................................................................................................ .44 5 STABLE ISOTOPE ANALYSIS...............................................................................48 Background.................................................................................................................48 Materials and Methods...............................................................................................54 Results........................................................................................................................ .57 6 DISCUSSION.............................................................................................................67 7 CONCLUSIONS........................................................................................................80 APPENDIX A MESOWEAR VALUES LISTED BY SAMPLE.......................................................82 B SERIAL STABLE ISOTOPE VALUES....................................................................86

PAGE 5

v LIST OF REFERENCES...................................................................................................88 BIOGRAPHICAL SKETCH...........................................................................................102

PAGE 6

vi LIST OF TABLES Table page 2-1 Biochronological ranges of the Willacoochee Creek Fauna....................................23 3-1 Systematic and morphological informati on about the taxa used in the mesowear analysis.....................................................................................................................35 3-2 Observed percentages of mesowear at tributes (% high and % low refer to the percentage of specimens with high or low occlusal relief and % sharp, % round, and % blunt refer to the pe rcentage of specimens with sharp, round or blunt cusp shape).......................................................................................................................36 3-3 Dietary classifications based on hierarchical clus ter analyses of mesowear attributes from Table 3-2..........................................................................................36 4-1 Individual microwear counts for 3 specimens of Acritohippus isonesus and 7 specimens of Neohipparion trampasense ................................................................46 4-2 Calculated average microwear values and percentages for Acritohippus isonesus and Neohipparion trampasense ................................................................................47 4-3 Isotopic data for equids fr om 4 central Florida sites................................................47 5-1 List of the 24 specimens analyzed fo r stable carbon and oxygen isotope analysis..60 5-2 Bulk stable carbon and oxygen isotope values for Willacoochee Creek Fauna.......61 5-3 Descriptive statistics of the 13C and 18O values for 8 herbivores from the Willacoochee Creek Fauna.......................................................................................62 6-1 Isotopic data for equids fr om 4 central Florida sites................................................79 A-1 Abbreviations: UF ID = catalogue nu mber in Florida Museum of Natural History collections,...................................................................................................82 B-1 Abbreviations: ELC = Englehard La Camelia Mine, MGF = Milwhite Gunn Farm Mine, and LC2 = La Camelia 2 Mine.............................................................86

PAGE 7

vii LIST OF FIGURES Figure page 2-1 Index map of middle Miocene lo calities in northern Florida...................................22 2-2 Composite section of the Torreya Formation and the location of the Willacoochee Creek Fauna within the Dogtown Member.......................................24 2-3 Correlated stratigraphic sections of the Englehard La Camelia and Milwhite Gunn Farm Mines.....................................................................................................25 2-4 Fresh cut at the newest site, the Crescent Lake Mine, in Decatur County, Georgia.....................................................................................................................26 2-5 Stratigraphic and temporal distributi on of the 3 fossil s ites studied in the mesowear analysis, as well as a fourth (Moss Acres)..............................................27 2-6 Tooth positions.........................................................................................................28 3-1 Dendrogram illustrating the hierarchical cluster analysis of the 27 typical grazers, browsers, and mixed feeders fr om Fortelius and Solounias (2000)...........34 3-2 Examples of typical mesowear attributes.................................................................35 3-3 Dendrograms illustrating the hierarchical cluster analyses of 6 studied taxa amongst the 27 typical grazers, browsers and mixed feeders from Fortelius and Solounias (2000)................................................................................................37 5-1 Schematic of isotopic fractionati on between atmospheric carbon and C3 plants, as well as fractionation between C3 plants and rumina nt herbivores.......................59 5-2 Plot of bulk 13C vs. 18O values for the 8 herbivor es from the Willacoochee Creek Fauna..............................................................................................................63 5-3 13C values for serial samples of two Aphelops specimens.....................................64 5-4 18O values for serial samples of two Aphelops specimens.....................................64 5-5 13C values for serial samples of two Merychippus primus specimens...................65 5-6 18O values for serial samples of two Merychippus primus specimens...................65

PAGE 8

viii 5-7 13C values for serial samples of two Acriohippus isonesus specimens..................66 5-8 18O values for serial sampling of two Acritohippus isonesus specimens...............66 6-1 Plot of microwear index versus 13C values............................................................78

PAGE 9

ix Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science USING STABLE CARBON ISOTOPE, MICROWEAR, AND MESOWEAR ANALYSES TO DETERMINE THE PALEODIETS OF NEOGENE UNGULATES AND THE PRESENCE 0F C4 OR C3 GRASSES IN NORTHRN AND CENTRAL FLORIDA By Jonathan M. Hoffman December 2006 Chair: Jonathan I. Bloch Major Department: Geology Traditionally, hypsodont (high-crowned) teeth in North American ungulates (hoofed mammals) were thought to have co evolved with grasses during the middle Miocene. Isotopic evidence has demonstrated that tropical C4 grasses were not dominant and therefore not abundant enough to be respons ible for this adaptive radiation. It has been proposed that high-altitude C3 grasses were extensive throughout the Great Plains and were the dietary driving force behind th e grazing adaptations. This study will test this hypothesis to see if it applies to the middle Miocene of the Southeastern United States. The 13C values from 24 specimens of 8 ungulate taxa from the Willacoochee Creek Fauna, an assemblage of middle Mi ocene mammals from northern Florida and southern Georgia, are presented here to determine if there is a significant C4 grass component in mammalian paleodiets. The 13C values indicate that all 8 taxa were consuming C3 plant material, either browse or gra ss. Furthermore, microwear analyses

PAGE 10

x conducted on 3 specimens of the most hyps odont taxon indicate that the mammal was eating grass. Combined with the 13C data, this study concludes that C3 grasses were present in the middle Miocene of northern Florida and at least one hypsodont mammal was consuming them. This evidence supports a C3 grass hypothesis of hypsodont radiations. Also, this study combines the mesow ear paleodietary analys is with previously published isotopic data to 5 equi d populations from 3 sites in central Florida, ranging in age from ~9.5 Ma to ~1.5 Ma, to trace the possible influence of C3 grasses on ungulate diets. C3 grasses were the primary food source fo r these horses until approximately 7 Ma. After that, the horses fed on a mixed diet of C3 and C4 grasses until about 1.5 Ma. At that point in Florida, the abundance of C3 grasses had diminished and the grazers primarily fed on C4 grasses.

PAGE 11

1 CHAPTER 1 INTRODUCTION Today, over 25% of North American na tural biomes are nonforest (Webb, 1977). The modern vegetation of North America is a sharp contrast to vegetation at the beginning of the Cenozoic, when nearly all of North America was covered with forests (Webb, 1977). Traditionally, paleontologists have believed that, beginning in the Paleocene, parts of North America underwen t a stepwise progression from forest to savanna to grassland biomes (Webb, 1977). Fo r most of the Paleocene, North America was dominated by evergreen forests and cypress swamps (Wolfe, 1985; Wing and Tiffney, 1987). It has been pr oposed that grasses originated amongst this vegetation in the early Paleocene, although no direct evidence of grasses has been found in sediments of that age (Linder, 1986; Crepet and Fe ldman, 1991). Nearly all the mammals in the Paleocene belong to four orders: the Multiuberculata, Insectivora, Primates, and Condylarthra (Webb and Opdyke, 1995). These ma mmals were small to medium in size and were arboreal or scansorial (W ebb and Opdyke, 1995). The multituberculate Ptilodus for example, possesses morphological adaptations consistent with those of a modern tree squirrel, sugges tive of an arboreal habit (J enkins and Krause, 1983). The grassland transitional sequence bega n meekly, during the late Paleocene with the appearance of possible protosavannas in scattered open-country areas that constitute breaks in the forest coverage (Webb, 1977). In the late Paleocene Crazy Mountain Field of Montana, Simpson (1937) found that 90% of the fossils collected from floodplain sediments consisted of carnivores and ar chaic ungulates such as perptychids,

PAGE 12

2 phenacodontids, and arctocyonids. In the sa me area, taxa collected from swampy woodland deposits were typically smaller, arboreal mammals (Simpson, 1937). A similar pattern is apparent in late Paleocene and early Eocene se diments of the Rocky Mountain intermontane basins. The late Paleocene Fort Union Formation from that region consists of gray sediments indicative of swampy woodlands bounded by allu vial plains (Van Houten, 1945; Bown, 1980). Small arboreal mammals have been collected from these sediments, corroborating the environmental interpretation of woodlands (Van Houten, 1945). The early Eocene Willwood Formation, locat ed in the same area, exhibits redbanded flood plain sediments and ungulates suited for open-country habitation (Van Houten, 1945; Bown, 1980; Hickey, 1980; Wing, 1980). Van Houten (1945) concluded that the late Paleocene Rocky Mountain w oodlands had, by the early Eocene, developed flood plain savannas that existe d in breaks in the forest. A number of subtle modifi cations are evident in proba ble open-country taxa during the late Paleocene and ea rly Eocene. The condylarth Meniscotherium exhibits molarized premolars, molar crescents, and some curs orial limb elongation (G azin, 1965), attributes that improved the mastication of coarser vegetation and ope n-country locomotion. In the Torrejonian North American Land Mammal Age (NALMA) of the middle Paleocene, three orders of larger Asian immi grants arrived in North America: the Pantodonta, Taeniodonta, and Dinocerat a (Webb and Opdyke, 1995). Titanoides a late Paleocene pantodont, bears digging forelimbs that would have excavated coarse roots (Webb, 1977). Taeniodonts, large clawed opossum-like root grubbers, were the first mammals to develop hypsodont (high-crowne d) teeth (Patterson, 1949). Cr ested molars and molarized premolars are also seen at this time in th e uintatheres (Order Di nocerata), which bear

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3 "hornlike protuberances" indica tive of herding behavior s een in open-country ungulates (Wheeler, 1961). Global climate fluctuated during the Paleocene. Deci duous tree populations began increasing at about 63 Ma, indicative of coo ling climate (Rose, 1981) This cooling trend began near the boundary of the Torrejonian and Tiffanian and continued through the Tiffanian, accompanied by the disappearance of small mammals and an increased presence of larger mammals (Webb and O pdyke, 1995). The Tiffanian cooling trend was followed by the initial appearance of open-count ry habitats that co incides with a global warming trend at the end of the Tiffania n (Koch, Zachos, and Gingerich, 1992). This warming trend began in the middle Paleocene (about 59 Ma) and peaked and ended with the early Eocene Climatic Optimum (EECO, 52 Ma) (Zachos, Pagani, Sloan, Thomas, and Billups, 2001). At northern latitudes, the peak mean annual temperature in the early Eocene was between 25C and 30C, 15C to 20C warmer than today (Novacek, 1999). The warming trend and EECO are marked by a 1.5 decrease in 18O values from benthic foraminifera, the lowest such 18O values in the Cenozoic (Zachos et al., 2001). This global warmth had a major impact on both North American floral and faunal communities. Between 55 and 53 Ma, the numbe r of macrofloral sp ecies doubled in the Paleocene/Eocene of the Bighorn Basin (Wi ng, Alroy, and Hickey, 1995). Early Eocene fossil leaves exhibit drip-tips and smooth margins indicative of a tropical/subtropical climate (Wolfe, 1978; Prothero, 1994). The evergreen forests of the Paleocene had given way to early Eocene subtropical forests, while still maintaining some open-country enclaves (MacGinitie, 1974; Rose, 1981; Bown and Krause, 1981, 1987).

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4 The beginning of the Clarkfor kian (latest Paleocene), at about 56 Ma, is marked by the first major immigration episode of As ian mammals capable of exploiting the new North American open-country niches (Webb and Opdyke, 1995; Lofgren, Lillegraven, Clemens, Gingerich, and Williamson, 2004). Th e newly arrived Asian orders included the Tillodontia and Rodentia, as well as th e pantodont family Coryphodontidae (Rose, 1981; Krause and Maas, 1990). Many of these mammals had adapted to grazing lifestyles in Asia. For example, Coryphodon one of the Asian pantodonts that arrived in North America in the late Paleocene, is believed to have already been a hippo-like amphibious grazer that, based on canine grooves, rooted fo r food (Simons, 1960). In all, nine genera immigrated from Asia to North Amer ica in the Clarkforkian (Stucky, 1990). The Clarkforkian immigration episode continued into the Wasatchian, in the earliest Eocene (Webb and Opdyke, 1995). The Clarkforkian-Wasatchian boundary correlates with the Paleocen e-Eocene boundary at about 55 Ma (Gingerich, 2001). The early Wasatchian was subject to the larges t mammal immigration wave in the North American fossil record. At this time, Europ ean mammals crossed the North Atlantic over the Thulean land bridge (Webb and Opdyke, 1995). This immigration episode included the first North American appear ances of order Perissodactyla ( Hyracotherium ), order Artiodactyla ( Diacodexis ), the creodont family Hyaenodontidae, and the primate families Adapidae and Omomyidae (Rose, 1981). Dire ct evidence of grass during the late Paleocene and early Eocene is rare, but ther e are some fossil grasses that indicate the presence of protosavannas: the oldest North American grass macrofossil, early Eocene in age, comes from the Paleocene/ Eocene Wilc ox Formation of western Tennessee (Crepet and Feldman, 1991).

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5 The morphological subtleties visible during the late Pale ocene/early Eocene gave way, in the middle and late Eocene, to more pronounced adaptations and shifts in both floral and faunal communities due to the chan ging global climate. In the middle Eocene, the global climate began cooling again a nd becoming drier, as evident from a 3.0 increase in benthic foraminifera 18O values over a 17 million year span, from 50 Ma to 33 Ma (Savin, 1977; Zachos et al., 2001). The increase in 18O values in the middle Eocene (50 Ma) resulted entirely from a decrease in deep-sea temperature from about 12C to about 4.5C (Zachos et al., 2001). Subs equent ice sheet grow th began by the late Eocene (34 Ma) and was responsible for further 18O enrichment (Miller and Katz, 1987; Zachos, Stott, and Lohma nn, 1994; Zachos et al., 2001). It was also during the middle Eocene that the first signs of seasonal aridit y, such as evaporites and oxidized redbeds, appear in the Rocky Mountain region (Webb and Opdyke, 1995). As aridity and cooling increased in the middle Eocene, there was a major faunal turnover in the subtropical forests. By the end of the Duchesn ean, 80% of the terrestrial mammal genera present in the Uintan (the pr evious age) had become extinct (Savage and Russell, 1983; Stucky, 1990). The gradual disappearance of tropical forests in North America prompted the decline of arboreal creatures such as primates (Webb, 1977). The adapids and paromoyids, the last of the Nort h American primates, disappeared at the end of the Duchesnean (Prothero, 1994). The orders Condylarthra, Tillodontia, Dinocerata, and Taeniodonta also disappeared in the la te Duchesnean (~40 Ma), while many new Asian immigrants arrived, most not ably the eubrontotheres such as Duchesneodus (Webb, 1977; Emry, 1981; Krishtalka et al., 1987; Prothero, 1994).

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6 By the late Eocene, the cooler and drier climate allowed for the first true savannas to dominate the midcontinent (Webb, 1977; Wing and Tiffney, 1987). Savannas, as defined by Sears (1969), are any biomes that are subtropical opencountry plains with some trees, which includes areas such as t horn scrub and open deciduous forests, but do not include open steppe or gras slands. The savannas that appeared in the late Eocene were savanna woodlands, typified by the pres ence of the Leguminosae, Sapindaceae, and Anacardiaceae floral families, similar to those of the modern Chihuahua region of Mexico (Webb, 1977). As the global cooling continued, tropical fl ora and subtropical forests retreated south of the Rocky Mountains (Leopold and MacGinitie, 1972). Members of the grass family Poaceae are also present in the late Eocene. Representatives of the subfamily Pooi deae, from Tribes Stipeae (e.g., Stipa florissanti ) and Phalarideae, appear in the Florissant fl oral assemblage of Colorado, at about 34 Ma (MacGinitie, 1953; Stebbins, 1981). The presence of these two tribes, endmembers of two separate evolutionary lin eages, suggests that the Pooide ae was well-differentiated by the end of the Eocene (Stebbins, 1981). The new savanna woodland habitats were exploited by a number of adapting North American mammals, as well as by late Eocen e Asian immigrants already adapted to savanna habitats. The combined autochthounous and invasive taxa, which followed the Duchesnean faunal turnover, are termed the White River chronofauna (Emry, 1981). Chronofaunas are assemblages of species th at remain compositionally stable over a significant amount of time (Olson, 1952). The White River chronofauna consists of an increase in herbivore genera and species fr om the late Eocene through the Oligocene, beginning around 40 Ma (Krishtalka et al., 1987; Webb and Opdyke, 1995). The number

PAGE 17

7 of identified browsing mammalian genera rose from 8 in the Duchesnean to about 40 after the Duchesnean (Stucky, 1990). Likewise, the overall number of mammalian herbivore species rose from less than 40 to about 90 during the Eocene-Oligocene transition (Savage and Russell, 1983). The higher species numbers were maintained throughout the Oligocene (Webb, 1989). Nume rous modern mammalian families make their first appearance in North America dur ing the late Eocene, including: soricid insectivores; sciurid, castorid, cricetid, and heteromyid r odents; leporid lagomorphs; canid and mustelid carnivores; camlids; ty assuids; and rhinocerotids (Webb and Opdyke, 1995). By the middle Oligocene, the White River chronofauna had become the first North American chronofauna to exhibit si gnificant diversity of hypsodont herbivores, from rodents to ungulates (Gregory, 1971; Webb and Opdyke, 1995). These hypsodont taxa include: leporids, castorid s, eomyids, rhinocerotids, hypertragulids, oromerycids, and oreodonts (Webb, 1977). The oromerycid Montanatylopus for example, has molars significantly more hypsodont than its brachydont sister taxa (Prothero, 1986). The newest Asian taxa, introduced through the connec tion of the North American and Asian continents (McKenna, 1972), included a suite of selenodont (crescent-toothed) artiodactyls already adapted fo r savanna feeding (Webb, 1977). Included in this group are the families Camelidae, Hypertragulidae, Le ptomerycidae, and Agriochoeridae (Webb, 1977). The newly introduced taxa flourishe d in the fresh savanna environments. One taxon native to North America, Hyopsodus acquired more lophodont (crest-toothed) molars to chew coarser food (Gazin, 1968). Nativ e rodents, such as the protoptychids and cylindrodontids, developed open-country loco motive adaptations as well as dentitions

PAGE 18

8 suited for coarser foods (Wood, 1962; Bl ack and Dawson, 1966; Galbreath, 1969; Wahlert, 1973). Larger herbivores exis ted in two general groups: semiamphibious streamdwellers such as amynodont rhinos and long-limbed, cursorial taxa that roamed the interfluves, such as equids ( Mesohippus ) and selenodont artiod actyls (Wall, 1982). These adaptations, along with the diversif ication of many of these cursorial and hypsodont taxa, mark the dominance of the woodland savannas that had become widespread in the Oligocene (Webb, 1977). It is also likely that the White River chronofauna established a positive feedback loop w ith the savanna biomes: Large herbivores preferred feeding in more open woodla nds; in turn, expansion of open formations facilitated evolution of mixed-feeding herb ivores. (p., 192, Webb and Opdyke, 1995) Additionally, there was a nega tive correlation between browse rs and the spread of opencountry habitats (Webb and Opdyke, 1995). By the late Oligocene, browsers such as titanotheres had disappeared as woodland sa vannas continued to spread (Webb and Opdyke, 1995). The expansion of woodland savannas is supported not only by hypsodont radiations but other lines of both floral and faunal evid ence. Aquatic reptiles in the Rocky Mountain area underwent severe population decreases as a result of ar idity and seasonality during the late Eocene and Oligocene (Hutchinson, 1982). The late Eocene Florissant Flora of Colorado records a decrease in the percentage of entire-m argined leaves, indicating a drop in mean annual temperature from 10 C to ~12.5 C (MacGinitie, 1962; Wolfe, 1985). Additionally, pedological studies on th e Brule Formation of South Dakota (~33 Ma, early Orellan) and the Upper John Da y Formation in central Oregon (~30 Ma,

PAGE 19

9 earliest Arikareenan) sugges t the presence of desert bunch grasslands during the early/middle Oligocene (Retallack, 1 997; Retallack, 2001; Retallack, 2004). Grass, however, was still relatively rare in the fossil record of the Eocene and Oligocene (Frederickson, 1981; Webb and O pdyke, 1995; Jacobs, Kingston, and Jacobs, 1999). There are two plausible explanations for this rarity. The first is that woody shrubs dominated the landscape prior to th e profusion of grasses (Huber, 1982). The second possibility is that grasses suffer from a taphonomic bias, preventing the preservation of grasses despite their actu al abundance (Webb and Opdyke, 1995). Grasses are known to be abundant elsewhere during the middle Eo cene, including Australia (Truswell and Harris, 1982) and Europe (Litke, 1968). Immediately following the Eocene-Oligocen e transition, the Drake and Tasmania Passages opened (at ~31 and 32 Ma, respec tively), increasing ocean circulation and proliferating the global coo ling trend from the Eocene (Lawver and Gahagan, 2003). This also allowed the establishment and preser vation of permanent Antarctic ice sheets (Hambrey, Ehrmann, and Larsen, 1991). The decrease in global temperature continued until the late Oligocene (26 to 27 Ma), wh en another warming trend began (Miller, Wright, and Fairbanks, 1991; Wright, Miller and Fairbanks, 1992). This warming trend reduced Antarctic ice sheet volume until the middle Miocene, ~15 Ma (Miller et al., 1991; Wright et al., 1992). There were some short glaciation events interspersed throughout this approximately 12 million year interval (W right and Miller, 1993). This warming reached its zenith during the middle Miocene Climatic Optimum (MCO), from 17-15 Ma, which is evident from decreased 18O values (Vincent, Killingley, and Berger, 1985; Flower and Kennett, 1995). Oceanic and atmo spheric cooling and ice sheet growth

PAGE 20

10 followed the MCO, marked by about a 1 increase in foraminifera 18O values from 14.0 to 13.8 Ma (Flower and Kennett, 1995). There are two hypotheses for the mechanism that drove the middle Miocene climate variability: greenhouse gases and o ceanic circulation (Zachos et al., 1994). From 16.5 to 13.5 Ma, overlapping the MCO, benthic foraminifera 13C values were elevated as high as 2.2 (Vincent and Berger, 1985). This event, termed the Monterey Excursion, possibly resulted from the draw down of atmospheric p CO2 through organic carbon burial in marginal marine sedi ments (Vincent and Berger, 1985). It has been proposed that the Monterey Excursion drove middle Mi ocene climate variability, although there is a 2.5 million year lag between the onset of the proposed p CO2 draw down (16.5 Ma) and the atmospheric cooling indicated by the 18O increase at 14 Ma (Vincent and Berger, 1985; Hodell and Woodruff, 1994). Atmospheric CO2 levels and global climate may have remained high during this la g due to the outgassing of CO2 from the Columbia River Flood Basalt from 17 to 14.5 Ma (Hodell and Woodruff, 1994). However, other researchers have suggested that atmospheric CO2 levels were low from 17 Ma to 14 Ma (Pagani, Freeman, and Arthur, 1999 ; Flower, 1999; Royer et al., 2001). The middle Miocene climate variability, therefore, may ha ve resulted from the opening and closing of tectonic gateways that altered oceani c circulation (Woodruff and Savin, 1989, 1991; Raymo, 1994). The first immigration episode of the Mio cene occurred at approximately the same time as the beginning of the MCO, from 18-17 Ma in the middle Hemingfordian (Webb and Opdyke, 1995). These Asian immigrants include eomyid rodents, the biostratigraphically impor tant cricetid rodent Copemys and the first true cats in the New

PAGE 21

11 World such as Pseudaelurus (Webb and Opdyke, 1995). The immigration also included four megaherbivores: the rhinocerotids Teleoceras and Aphelops and the proboscideans Miomastodon and Gomphotherium (Webb and Opdyke, 1995). It is assumed that these megaherbivores modified the savanna landscape much like modern elephants, however, there is no direct evidence to support this hypothesis (Owen-Smith, 1988). These immigrants comprise part of the S heep Creek chronofauna of the early and middle Miocene. The Sheep Creek chronofaun a is also important because it chronicles the grazing advancement of horses, with th e transition of the br owsing/mixed feeding Parahippus to the grazing Merychippus (Hulbert and MacFadden, 1991). Treeless grassland prairies were initially thought to have become widespread in the Great Plains at the beginning of the Bars tovian Land Mammal Age (middle Miocene, ~ 15.8 Ma), replacing the steppe savannas (Kowalevsky, 1872; Webb, 1983). This timing would correlate with the end of the middle Miocene climatic optimum. This interpretation for grassland expansion was based largely on the prevalence of mammals with grazing adaptations, especially horses, a nd has been viewed as a classic example of coevolution. Mesodont horses such as Parahippus gave way to hypsodont horses, like Merychippus and Hipparion that also exhibited increased enamel folding and cement deposition on the cheek teeth (Webb, 1977). These adaptations, which improved the grinding surface of the tooth, were also featured in camels, pronghorns, oreodonts, rhinoceroses (diceratherine and teleo ceratine), and at least four genera of gomphotheriid proboscideans (Webb, 1977). The diversification of these taxa is direc tly correlated to the degree of hypsodonty; th e higher-crowned lineages experienced greater radiations (Webb, 1977). The succession of grazers, starting at the beginning of the Barstovian

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12 (15.8 Ma) and lasting through the end of the Clarendonian (8.8 Ma), has been termed the 'Clarendonian chronofauna' (Webb, 1983). It ha s also been suggested that this faunal succession (and therefore the appearance of gr asses) began during the beginning of the late Hemingfordian at 17.5 Ma (T heodor, Janis, and Broekhuizen, 1998). In addition to dental adaptations fo r grazing, many ungulates acquired elongated limb modifications for open-country loco motion (Webb, 1977). Hypsodont horses, for example, developed digital springing ligamen ts at about the same time that they developed grazing dentitions (Camp and Smit h, 1942). Rodents also adapted to savanna habitats in the Miocene. Their teeth becam e higher-crowned (Rensberger, 1973) and their limbs adapted for burrowing habits (Webb, 1977). Mylagaulids (Fagan, 1960), heteromyids (Lindsay, 1972), geomyoids (R ensberger, 1971), and ochotonid rabbits (Green, 1972) all diversified into an array of hypsodont burrowers. The abundance of needlegrass taxa, specifically Stipidium and Berriochloa in the High Plains region (Elias, 1942) seemingly confirmed the dominance of gra sslands in the Grea t Plains during the middle Miocene. The traditional view of grassland evolu tion was modified by a study of the late Miocene (12 Ma) Kilgore Flora of Nebraska This floral assemblage depicted an environment consisting of savannas with mesi c and open grassy forests, but lacking any open prairies (MacGinitie, 1962). Faunal eviden ce corroborates this claim. The presence of arboreal rodents, primat es, insectivores, brachydont browsers and mixed feeders suggests that the Great Plains was still a w oodland savanna with riparian forests through the late Miocene (Gregory, 1971). Grasses, therefore, were abunda nt through the late Miocene, but grasslands had yet to domina te the landscape. It was not until the Late

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13 Hemphillian (Early Pliocene, ~5 Ma), that tr eeless steppe grasslands swept across the Great Plains. The vertebrate evidence for th is consists of the ab sence of arboreal and browsing taxa, a limited diversity of grazing taxa, and an overa ll lower diversity of all vertebrate taxa (Gregory, 1971). The traditional grassland story has been further modified, in more recent years, from multiple types of studies. Paleosol studies indicate the presence of short sod grasslands in the Great Plains region in the early Miocene, ~19 Ma, and tall sod grasslands by the late Miocene, ~7 Ma (Retallack, 1997; Reta llack, 2001). Paleosol studies also indicate the presen ce of sod grasslands in the Hemingfordian (early Miocene, ~ 19 Ma) in central Oregon (R etallack, 2004). Phytoliths, th e silica granules found in many plants, have also been used to identify savanna environments. Morphological studies on phytolith assemblages from northwe stern Nebraska indica te that open-habitat grasses were present in savanna and w oodland environments by the early Miocene (Strmberg, 2002; Strmberg, 2004). The most extreme revisions have come from stable isotope studies. Stable carbon isotopes from paleosols and fossil tooth enam el from various regions reveal a global increase in the C4 biomass during the late Miocene a nd early Pliocene (7 Ma) (Quade et al., 1992; Cerling, Wang, and Quade, 1993; Wang, Cerling, and MacFadden, 1994; MacFadden and Cerling, 1996; Cerling et al., 1997b). This observation was based primarily on the bioapatite of the fossil teeth, which reflect the C3/C4 plant constituents of the animals diet through 13C ratios. It was proposed that the increase in C4 biomass was due to lowered concentrations of CO2 in the atmosphere, which would have caused the less efficient C3 plants to diminish and the more efficient C4 plants (mainly tropical

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14 grasses) to flourish (Ehleri nger, Sage, Flanagan, and Pear cy, 1991; Cerling et al., 1993; Cerling et al., 1997b). This theory has b een countered by Morgan, Kingston and Marino (1994), who claim that there was no expansion of the C4 biomass and no connection between the atmosphere a nd any changes in the C3/ C4 biomass. Rather, Morgan and colleagues suggest that the apparent increase in C4 consumption by mammalian herbivores is the result of faunal immigration or in situ speciation, not a change in the floral populations. Also, the proposed decrease in atmospheric CO2 concentrations has been challenged due to a lack of direct evid ence of a change in th e partial pressure of CO2 (Pagani et al., 1999). The isotopic evidence modifies the grassl and story in two ways: (1) It pushes the dominance of C4 grasslands back as early as 7 Ma and, more importantly, (2) Denies a significant C4 presence before 7 Ma, casting doubt on the idea that grassy savannas preceded the steppe environment in the Great Plains. Initially, the isotopic and faunal evidence provided an interesting dilemma. The faunal morphological changes suggested a strong presence of grass, presumably C4, in the Great Plains at 15.8 Ma (Webb, 1983) or 17.5 Ma (Theodor et al., 1998). Howe ver, a major global increase in C4 biomass is not documented in the paleodiets unti l 7 Ma (Cerling et al., 1993). This indicates an apparent change in faunal morphology that began 8.8 to 10.5 million years before the ungulates began eating C4 grasses, and therefore long before the dominance of the grasses believed to have caused the adaptations (Fox and Koch, 2003). More recent isotopic evidence has addr essed this discrepancy by pushing the appearance of C4 grasses back prior to the or iginal 15.8 Ma age based on faunal morphology. Fox and Koch (2003) looked at pa leosol stable isotopes from the Great

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15 Plains region of North Amer ica and suggested that the C4 biomass first appeared no later than the early Miocene (about 23 Ma), but did not become dominant until the late Miocene (as evident from the biomass shift s een at 7 Ma). Based on the paleosol and faunal data, Fox and Koch (2003) suggested that typical Great Pl ains habitats in the late Miocene consisted of C3 trees and shrubs over a light carpet of grass. The apparent temporal gap between grazer morphology and C4 dominance could then be the result of the expansion of cool climate C3 grasses (Wang et al., 1994; Fox and Koch, 2003). Expansive C3 grasses in the middle Miocene could have been responsible for the ungulate grazing adaptations, since C4 grasses were still too relatively low in abundance to cause such expansive ad aptive radiations (Fox and Koch, 2003). The idea of C3 grasses driving hypsodonty radiations deno tes a paradigm shift in how paleodiets are assessed through stable isotopes. Initially, 13C values that reflected C3 diets were typically ascribed to browse materi al, such as shrubbery and leaves. C3-consumers were then categorized as browsers while C4 consumers were categorized as grazers. This was due, in large part, to the assumption that paleoenvironments are analogous to modern environments. This assumption has recently b een reevaluated. Wang et al (1994) first suggested that a unique grassland envi ronment composed of low-latitude C3 grasses could have existed in the middle Miocene due to lower concentrations of atmospheric CO2. Janis, Damuth, and Theodor (2002) conc luded that early Mi ocene ungulates are unlike any ungulates from modern grassland and forest environments and, therefore, represent a paleoenvironment unlike any s een today. This interpretation has been supported by Fox and Koch (2003), who proposed the hypothesis of expansive C3 grasses

PAGE 26

16 in woodland environments. Woodland savannas with C3 grasses would then constitute a unique environment with no modern analogues. In order to further assess this claim, and to evaluate the spread of C4 grasses across North America, this study focuses on the mi ddle Miocene to early Pleistocene (15 Ma) of northern/central Florida and southern Geor gia and seeks the presence of grasses in the diets of ungulates. Of partic ular interest is the Willacoochee Creek Fauna, an early Barstovian (~15 Ma) faunal assemblage that is mostly composed of possible early grazers or mixed feeders (ungulates bearing me sodont to hypsodont teeth). This faunal community existed at a pivotal point in the ev olutionary history of mammals; when openhabitat morphologies rapidly expanded. This study utilizes three methods of paleodiet analysis: stable carbon isotope analysis, meso wear analysis, and microwear analysis. The combination of stable isotopes and mesowear or microwear makes it possible to either substantiate or refute the presence of C4 grasses in the paleodiets of middle Miocene ungulates, as well as address alternative dr iving mechanisms for the adaptation of hypsodonty. The objectives of this study are (1 ) Characterize the diet ary habits of the community of herbivores from the Willacoochee Creek Fauna, (2) Determine the presence of any grasses, C3 or C4, in northern Florida during the middle Miocene, and (3) Determine the presence of any grasses, C3 or C4, in Florida leading up to the carbon biomass shift at ~7 Ma.

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17 CHAPTER 2 FIELD AREA AND FAUNA The taxa in this study were excavated from sediments fr om seven sites in Florida and Georgia. Three of the sites are located in northern Gadsen County, Florida: the Englehard La Camelia Mine, the Milwhite Gunn Farm Mine, and the La Camelia 2 Mine (Figure 2-1). Sediment samples were colle cted from the Englehard La Camelia and Milwhite Gunn Mines in the late 1980's by field crews from the Florida Museum of Natural History (FLMNH) and the University of Florida Department of Geological Sciences (Bryant, 1991). Vertebrate fossils were also collected from these sites. Most of the fossils were recovered from spoil piles, bu t these piles were positively associated with the Dogtown Member of the Torreya Formati on (Bryant, 1991). These fossils comprise the Willacoochee Creek Fauna (WCF) assemblage an early Barstovian (middle Miocene) assemblage of mammals, birds, amphibians, and reptiles found in the Dogtown Member (Bryant, 1991). The early Barstovian desi gnation of the assemblage is based on the presence of Copemys Perognathus, Rakomeryx and Ticholeptus as well as the overlapping age ranges of several other ma mmals (Bryant, 1991; Table 2-1). The beginning of the Barstovian is defined by the appearance of Copemys and the early Barstovian is characterized by the appearance of Perognathus Rakomeryx and Ticholeptus (Tedford et al., 1987). The WCF bear s mammals with known age ranges that begin in the early Barstovian, restricting the age of the WC F to an upper limit of early Barstovian (Bryant 1991). The overlapping ag e ranges of other mammals, such as those

PAGE 28

18 of the Merychippine horses, support this age correlation. The absolute age of the early Barstovian is between about 16.6 to 14.4 Ma (Tedford et al., 1987). The Torreya Formation is part of the Hawt horn Group and it is the only part of that group that is present in the eastern Flor ida panhandle (Scott, 1988; Huddlestun, 1988). The formation is siliciclastic with scattered carbonate and phosphate deposits and can be found throughout the eastern Florida panhandle and into southern Georgia (Bryant, 1991). Bryant (1991) describe d the Dogtown Member of the Torreya Formation as "largely clay, with varying amounts of sand and dolomite, and is primarily present in Gadsen County, Florida, and adjacent Decatur County, Georgia" (Figure 2-2). The Englehard La Camelia Mine was designated as the type section of the Dogtown Member (Bryant, 1991). Vertebrate foss ils are found in the sand and sa nd/clay layers (Figure 2-3). As mentioned earlier, the Milwhite Gunn Fa rm Mine also belongs to the Dogtown Member, but it represents a uni que lithology. It consists of well-indurated, weatheringresistant, carbonate-cemented sa ndstone (Bryant, 1991). Bryant (1991) suggested that the outcrop at the Milwhite Gunn Farm Mine repr esented a "subaerial exposure surface, but no pedogenic horizonation is preserved." The Milwhite Gunn Farm Mine and Englehard La Camelia Mine layers are contemporaneous, based on the in situ presence of the rodents Copemys and Perognathus at both sites (Bryant, 1991). There are two new sites, the La Camelia 2 and Crescent Lake Mines. The La Camelia 2 Mine is located in northern Gadsen County, Fl orida, near the original Englehard La Camelia Mine site. Over 2,000 pounds of sediment, as well as some vertebrate fossils, were collected from La Camelia Mine 2 by an FLMNH/UF Geology Department field crew in May, 2004. Like the previous sites, the sediment samples and

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19 fossils were collected from spoil piles at th is site. These piles, however, were positively associated with a single unit at the site. This unit consists of interfingering sand and clay layers and has been correlated with the D ogtown Member and aged as early Barstovian. The unit correlation is based on lithology and th e Barstovian age, wh ich is derived from the overlapping presences of Aphelops sp., which first appears in the Late Hemingfordian, and Acritohippus isonesus (Figure 2-2). The second new site, the Crescent Lake Mi ne, is located 15 miles north of the Florida-Georgia Border in Decatur County. Vertebrate fossils and sediment were collected from this site by FLMNH field cr ews in May, 2005. Unlike th e other sites, these samples were collected in situ along a fresh cut at the mine (F igure 2-4). The sediments at the Crescent Lake Mine constitute a clayey sand layer representing terrestrial and marine environments. Marine depositional environmen ts are evident by the presence of abundant invertebrate fossils, such as gastropods, bivalves, and echinoi ds (sea urchins), as well as garfish scales. Based on the lithology of th e unit and mammal assemblage, this site correlates with the Dogtown Me mber of the Torreya Formati on and an early Barstovian age. The age is based on th e presence of the brachydont Anchitherium clarencei and the mesodont Merychippus primus two horses with biochronologi cal ranges in the WCF that extended, and terminated, in the early Ba rstovian (Bryant, 1991; Figure 2-2). Additionally, the hypsodont horse Acritohippus isonesus and the rhino Aphelops have overlapping ranges in the Ba rstovian (Bryant, 1991). The two sites discovered in the 1980's (E nglehard La Camelia and Milwhite Gunn Mines) have both been analyzed for stront ium-isotopic and paleomagnetic dating. Four reliable 87Sr/86Sr age estimates place the Dogtow n Member between 16.6 1.0 and 14.7

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20 1.5 Ma (Bryan, MacFadden, and Mueller, 1992) The Dogtown Member is entirely of reversed polarity, and, with biochronologic data, the unit correlates with Chron C5B-R (Bryant et al., 1992). This correlation narro ws the age of the Dogtown Member, and therefore the WCF, to between 16.2 and 15.3 Ma (Bryant et al., 1992). This range has been restricted further, to between 1 5.9 and 15.3 Ma, based on the HemingfordianBarstovian boundary (Woodburne, Tedford, and Swisher, 1990). Br yant et al. (1992) also determined that the Dogtown Member is time-transgressive, with sediments getting younger to the north. In addition to the middle Miocene sites, this study looks at younger sediments to trace the presence of grasses in Florida. Th e three younger sites are al l located in central Florida. Ages for two of th ese sites are determined by biochronology. The Love Bone Bed Site is late Miocene and designated as late Clarendonian in age (~9.5 Ma) and the Upper Bone Valley Formation is early Pliocen e and late Hemphillia n (~4.5 Ma) (Figure 2-5; Hulbert, 1992; Morgan, 1994). The accur acy of these ages is within about 0.5 Ma (MacFadden and Cerling, 1996). The third site is the Leisey Shell Pit, which has been dated at approximately 1.5 Ma based on biochronological, 87Sr/86Sr, and paleomagnetic data (Webb et al., 1989). The accuracy of this age is about 0.1 Ma and places the Liesey Shell Pit in the early Pleistocene w ith an early Irvingtoni an age (Figure 2-5). These three sites were chosen for this study because stable carbon is otope analyses have been previously conducted on large populations of fossil horses from these sites (MacFadden and Cerling, 1996). These large pop ulations are also ideal for mesowear analyses.

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21 The specimens analyzed in this study span approximately 14 million years. Specimens from the Englehard La Camelia, Milwhite Gunn Farm, and La Camelia 2 Mines are representatives of the WCF fr om the Dogtown Member of the Torreya Formation and are of early Barstovian (about 15.9 to 15.3 Ma) age (Bryant, 1991). Before any analyses could be conducted, it was necessary to identify all of the specimens. Despite the previous description of the WCF by Bryant (1991), many of the collected fossils were still unidentified and not catalogued. Additionally, all of the fossils from the new site needed to be identified and catalogued. These fossils, which are all teeth, were identified by referencing published literature as well as identified specimens from the FLMNH collections. The vast major ity of unidentified specimens were horse teeth. In addition to identifying the taxon, the tooth position was determined for each tooth by comparing the widths of the parastyl e and mesostyle and assessing the angle of the mesostyle and plane of occlusal surface (F igure 2-6). Typically, the parastyle is wider than the mesostyle in horse molars and vice versa for horse premolars (Bode, 1931). More posterior-leaning mesostyle angles and sh allower angles of the occlusal plane are indicative of molars, while more anterior ly-leaning mesostyles and more pronounced angles of the occlusal plane are apparent in premolars (Bode, 1931). Identification of the tooth position is important in this study since paleodiet anal yses often use specific teeth as a standard for paleodiet assessment.

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22 Figure 2-1. Index map of middle Miocene local ities in northern Florida. 1 = Milwhite Gunn Farm Mine, 2 = Englehard La Camelia Mine and La Camelia 2 Mine. All of the Willacoochee Cr eek Fauna taxa were collected from the Dogtown Member of the Torreya Formation. (Modi fied with permission from Bryant, 1991)

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23 Table 2-1. Biochronological ranges of th e Willacoochee Creek Fauna. Solid lines indicate known ranges and asterisks indica te range extensions. Note that all of the ranges overlap in the early Barstovian. Also, Ticholeptus hypsodus Bouromeryx cf. parvus and Rakomeryx sp. all occur only in the early Barstovian. These ranges denote an ear ly Barstovian age for the Dogtown Member of the Torreya Formation. (Modified with permission from Bryant, 1991) TAXONHEMINGFORDIAN BARSTOVIAN CLARENDONIAN EARLYLATEEARLYLATEEARLYLATE Lanthanotherium sp. Mylagaulus sp. cf. Protospermophilus sp. Perognathus cf. minutus Proheterom y s sp. Copemys sp. Cynorca cf. proterva Ticholeptus hypsodus Bouromeryx cf. parvus Rakomeryx sp. Anchitherium clarencei Merychippus gunteri Merychippus primus Acritohippus isonesus Aphelops sp. KNOWN BIOCHRONOLOGICAL RANGE BIOCHRONOLOGICAL RANGE EXTENSION ********* ********* ********* *********

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24 Figure 2-2. Composite section of the To rreya Formation and the location of the Willacoochee Creek Fauna within th e Dogtown Member. Note that the Dogtown member is composed mostly of clayey sand and some clay. (Modified with permission from Bryant, 1991)

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25 Figure 2-3. Correlated stratigra phic sections of the Englehar d La Camelia and Milwhite Gunn Farm Mines. Note that the W illacoochee Creek Fauna are found in layers composed of clayey sand, sa nd, and sand with carbonate cement. (Modified with permission from Bryant, 1991)

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26 A) B) Figure 2-4. Fresh cut at the newest site, the Crescent La ke Mine, in Decatur County, Georgia. A) Cross-section view of sand and clay layers above the fossiliferous layer. B) Bottom of the cut, where the fossiliferous clayey sand is exposed. In the foreground is where terr estrial vertebrate fossils were found, while marine invertebrates were found elsewhere on the cut.

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27 Figure 2-5. Stratigraphic and temporal distribution of the 3 fossil sites studied in the mesowear analysis, as well as a four th (Moss Acres) discussed later. Neohipparion trampasense Cormohipparion plicatile and Cormohipparion ingenuum are from the Love Bone Bed, Nannippus aztecus is from the Upper Bone Valley Formation, and Equus leidyi is from the Leisey Shell Pits. (Modified with permission from MacFadden and Cerling, 1996)

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28 A) B) Figure 2-6. Tooth positions. A) The modern hor se jaw with the angles of the mesostyles and occlusal surfaces for each tooth position. Abbreviations: pm2 = upper 2nd premolar, pm3 = upper 3rd premolar, pm4 = upper 4th premolar, m1 = upper 1st molar, m2 = upper 2nd molar, m3 = upper 3rd molar, pm1 = lower 1st premolar, pm2 = lower 2nd premolar, pm3 = lower 3rd premolar, m1 = lower 1st molar, m2 = lower 2nd molar, m3 = lower 3rd molar. B) Buccal view of upper 4th premolar (a) and upper 1st molar (b). Note the differences in parastyle and mesostyle widths and the differences in angles of the plane of occlusal surface. (Modified with permission from Bode, 1931)

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29 CHAPTER 3 MESOWEAR METHOD The mesowear method was devised by Fort elius and Solounias (2000) as a quick and inexpensive process of determining the lifelong diet of a taxon. They determined that, for extant mammals, broad conclusions on the diets, such as a grazer or browser classification, can be deduced from the shape of the buccal cusps (either the paracone or metacone) and the relative difference in heig ht between the tip of the cusps and the intercusp valley. The robustness of this method was confirmed by blind test studies that revealed that there are no statistical differe nces in the scoring of attributes between individual researchers (Kaiser et al., 2000). The attributes that are evaluated, termed cusp shape and occlusal relief, were originally only applied to the upper second mo lar (M2) and require at least 20 specimens to obtain a reliable classification. Forteliu s and Solounias (2000) used cusp shape and occlusal relief to establish a "typical" se t of 27 extant browsers, grazers, and mixed feeders. This set was illustrated in a hierar chical cluster analysis (Figure 3-1), which shows clusters of mammals that had similar wear (attritionor abrasion-dominated). The classification of each cluster (e.g., graze r) was confirmed by direct observations made on the diets of the animals. The mesow ear technique can be extended to an extinct taxon, which can then be included in the hier archical cluster analys is to determine its dietary classification. Mesowear analyses require large sample populations (>20), which can be problematic for some localities, but th e method yields an accura te depiction of an animals average lifelong diet.

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30 In a study on hipparionine and extant equi ds, the mesowear method was extended to broaden its application beyond the upper M 2, to specific combinations of the upper third premolar (P3), upper fourth premolar (P4), upper first molar (M1), and the upper third molar (M3) (Kaiser and Solounias, 2003). This study was conducted with the goal of expanding the application of the mesow ear method beyond ungulate populations with an abundance of M2s. The extended mesowear method, the combination of tooth positions that yielded results most consistent with the M2 results, was that of the P4+M1+M2+M3 teeth. However, the extended method still requires positive identification of the tooth positions. While this is not problematic when studying associated teeth, it can be difficult to identify isolated teet h. This is especially true for e quids. Bode (1931) showed that it was possible to identify tooth position of unassociated teeth through the anterior-posterior tilt of each tooth, but it has been noted that this method is time-consuming and does not always result in a positiv e identification (Hulbert, 1987) This problem is often encountered when trying to distinguish be tween a P3 and P4. Kaiser and Solounias (2003) showed that the P3 in hipparionine equi ds was an unreliable i ndicator of paleodiet, causing a shift towards a grazer classification. A dditionally, they showed that the P4 is a reliable indicator, particularly when gr ouped with molars (as in the extended combination of P4-M3). To ensure correct di etary classifications based on unassociated teeth, this study will apply the mesowear method only to molars, avoiding dubious premolars. Previous studies have shown that anal yses based on M1s and M2s yield the same classifications as analyses based on only the M2s (Kaiser and Solounias, 2003; Hoffman, unpublished).

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31 Materials and Methods Mesowear analyses were conducted on five e quids from the younger central Florida sites: Neohipparion trampasense Cormohipparion plicatile and Cormohipparion ingenuum from the Love Bone Bed Site (~9.5 Ma); Nannippus aztecus from the Upper Bone Valley Formation (~4.5 Ma), and Equus leidyi from the Leisey Shell Pit (~1.5 Ma) (Table 31). Based on dental and post-cranial morphology, Neohipparion trampasense is a probable grazer to mixed feeder while the Cormohipparion species are both expected to be mixed feeders (MacFadden and Cerling, 1996). The taxon analyzed from the Upper Bone Valley Formation is Nannippus aztecus an expected grazer. Finally, Equus leidyi, an extremely hypsodont grazer from the Le isey Shell pit, was also analyzed. Following the techniques described in Fo rtelius and Solounias (2000), the cheek teeth of six different taxa we re assessed for mesowear analysis, in terms of cusp shape and occlusal relief (Figure 32). The cusp shape rating (s harp, round, or blunt) describes the shape of the apex of the sharper cusp. The occlusal relief descri bes the height of the cusps (high or low) relative to the valley between them. This rating can be quantified by drawing a line that connects the apices of th e two cusps, then measuring the vertical distance between that line and the center of cu sp valley. This value is then divided by the length of the whole tooth. For equids, values greater than 0.1 signify high occlusal relief and values below 0.1 signify low occlusal relief (Fortelius and Solounias, 2000). To avoid teeth that were in the early or late stages of wear at time of deposition, only teeth that are 25% to 75% of the maximum crown he ight were analyzed. Waterworn teeth were also excluded from the sample set. When n ecessary, a magnifying lens was used in rating the attributes.

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32 As stated in Fortelius and Solounias ( 2000), the mesowear signal becomes stable when there are more than 20 teeth, although a reasonable approximation is attained at about 10 samples. In this study, at least 20 samples were measured for each taxon to ensure correct classifications. The teeth that were analyzed include positively identified M1s and M2s, as well as molars that coul d be either an M1 or an M2. Once the measurements were recorded, the percentage s for each attribute were calculated. Next, these percentages were examined by hierarchical cluster analyses, using SPSS v.11.5 software, to determine the dietary classifica tion of each taxon. The variables entered into the hierarchical cluster analyses are percen tage high occlusal reli ef, percentage sharp cusp shape, and percentage blunt cusp shape. Complete linkage and normalized Euclidean distance were used in the analys is, following Fortelius and Solounias (2000). Each taxon was entered into a separate clus ter analysis, to avoi d altering the morphology of the dendrogram and possibly yielding biased clusters. The cluster placement of each fossil taxon was used to determine its dietary classification. For example, a taxon that is located within the cluster of typical extant grazers would be classified as a grazer. Results The cusp shape and occlusal relief rati ngs for each sample are listed in the Appendix A. The calculated percentages of th e attribute ratings for each taxon are listed in Table 3-2. In the hierarchical cluster analyses, all five horses ( Neohipparion trampasense Cormohipparion plicatile Cormohipparion ingenuum Nannippus aztecus and Equus leidyi ) are placed within the cluster of confirmed extant grazers (Table 3-3, Figure 3-3). N trampasense clusters closest to Ceratotherium simum (White rhinoceros), while C plicatile is closest to Damaliscus lunatus (topi) and C ingennum is placed closest to the subcluster of Alcelaphus buselaphus (hartebeest) and Connochaetes

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33 taurinus (wildebeest). Conversely, N aztecus forms its own subcluster with Alcelaphus buselaphus placing closer than Connochaetes taurinus. Finally, E lediyi is placed closest to Bison bison (American plains bison). All of these extant herbivores are typical hypsodont grazers.

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34 Figure 3-1. Dendrogram illustrating the hierar chical cluster analysis of the 27 typical grazers, browsers, and mixed feeders fr om Fortelius and Solounias (2000). Browser abbreviations are in upper case grazer abbreviations are in lower case, and mixed feeder abbreviations are upper and lower cas e. Abbreviations: AA= Alces alces RS= Rhinoceros sondaicus DB= Diceros bicornis OV= Odocoileus virginianus OJ= Okapia johnstoni GC= Giraffa camelopardalis OH= Odocoileus hemionus DS= Dicerorhinus sumatrensis Gg= Gazella granti Gt= Gazella thomsoni Om= Ovibos moschatus To= Taurotragus oryx Ts= Tragelaphus scriptus Cc= Cervus canadensis Cs= Capricornis sumatraensis Me= Aepyceros melampus, ab= Alcelaphus buselaphus ct= Connochaetes taurinus he= Hippotragus equinus rr= Redunca redunca ke= Kobus ellipsipyrmnus hn= Hippotragus niger eb= Equus burchelli eg= Equus grevyi dl= Damaliscus lunatus cs= Ceratotherium simum bb= Bison bison

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35 Table 3-1. Systematic and morphological information about the taxa used in the mesowear analysis. Abbreviations : MSCH = Maximum crown height measured from the occlusal surface to the base of the crown along the mesostyle. ( N trampasense tribe, age, and MSCH da ta from Hulbert, 1987; C plicatile and C ingenuum tribe, age, an MSCH data from Hulbert, 1988; N aztecus tribe, age and MSCH data from Hulbert, 1988 and Hulbert, 1990; Equus leidyi tribe, age, and MSCH data from Hulbert, 1995). Taxon Tribe Site and Age Level Molar MSCH Tooth Morphology Neohipparion trampasense HipparioniniLove Bone Bed, ~9.5 Ma 60 mm Hypsodont Cormohipparion plicatile HipparioniniLove Bone Bed, ~9.5 Ma 58 mm Hypsodont Cormohipparion ingenuum HipparioniniLove Bone Bed, ~9.5 Ma 49 mm Moderately hypsodont Nannippus aztecus HipparioniniUpper Bone Valley Fm., ~4.5 Ma51 mm Moderately hypsodont Equus leidyi Equinni Liesey Shell Pit, ~1.5 Ma 91.3 mm Extremely hypsodont Figure 3-2. Examples of typical mesowear at tributes. The three types of cusp shape are sharp, round, and blunt. The types of o cclusal relief are high and low. The dotted lines indicate the he ight of the occlusal relief, from the bottom of intercusp valley to the apex of the hi ghest cusp. (Modiefied with permission from Kaiser and Fortelius, 2003)

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36 Table 3-2. Observed percentages of mesowear attributes (% high and % low refer to the percentage of specimens with high or low occlusal relief and % sharp, % round, and % blunt refer to the percentage of specime ns with sharp, round or blunt cusp shape). Taxon N % high % low % sharp % round % blunt Neohipparion trampasense 49 24.5 75.5 2 57.2 40.8 Cormohipparion plicatile 45 35.6 64.4 8.9 60 31.1 Cormohipparion ingenuum 26 50 50 0 84.6 15.4 Nannippus aztecus 35 54.3 45.7 0 82.9 17.1 Equus "leidyi" 30 0 100 6.7 20 73.3 Table 3-3. Dietary classificat ions based on hierarchical cl uster analyses of mesowear attributes from Table 3-2. Taxon Site Age Classification Neohipparion trampasense Love Site 9.5 0.5 Ma Grazer Cormohipparion plicatile Love Site 9.5 0.5 Ma Grazer Cormohipparion ingenuum Love Site 9.5 0.5 Ma Grazer Nannippus aztecus Upper Bone Valley Fm. 4.5 0.5 Ma Grazer Equus "leidyi" Leisey Shell Pit 1.5 0.1 Ma Grazer

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37 A) Figure 3-3. Dendrograms illustrating the hierarch ical cluster analyses of 6 studied taxa amongst the 27 typical grazers, browsers and mixed feeders from Fortelius and Solounias (2000). A) Neohipparion trampasense (Nt). B) Cormohipparion plicatile (Cp). C) Cormohipparion ingenuum (Ci). D) Nannippus aztecus (Na). E) Equus leidyi (El). Note that all five equids place within the Grazers cluster. Browser a bbreviations are in upper case, grazer abbreviations are in lower case, and mi xed feeder abbreviations are in both upper and lower case. Abbreviations: AA= Alces alces RS= Rhinoceros sondaicus DB= Diceros bicornis OV= Odocoileus virginianus OJ= Okapia johnstoni GC= Giraffa camelopardalis OH= Odocoileus hemionus DS= Dicerorhinus sumatrensis Gg= Gazella granti Gt= Gazella thomsoni Om= Ovibos moschatus To= Taurotragus oryx Ts= Tragelaphus scriptus Cc= Cervus canadensis Cs= Capricornis sumatraensis Me= Aepyceros melampus, ab= Alcelaphus buselaphus ct= Connochaetes taurinus he= Hippotragus equinus rr= Redunca redunca ke= Kobus ellipsipyrmnus hn= Hippotragus niger eb= Equus burchelli eg= Equus grevyi dl= Damaliscus lunatus cs= Ceratotherium simum bb= Bison bison

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38 B) C)

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39 D) E)

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40 CHAPTER 4 MICROWEAR METHOD The microwear method is a dietary analysis that quantifies the microscopic wear on herbivore teeth. The consumption of herbivor ous diets leaves micr oscopic scratches and pits on the tooth enamel known as microwear. Studies on micr owear of extant herbivores with known diets have revealed a correlati on between microwear and diet (Teaford and Walker, 1984; Grine, 1986; Teaford, 1988; Solounias and Hayek, 1993) One noticeable trend is that grazers typically have more sc ratches than browsers while browsers bear more pits than grazers (Solounias and Se mprebon, 2002). These observations have led to the establishment of a Microwear Index (MI) (MacFadden, Solounias, and Cerling, 1999). For a stated area of enamel (e.g., 0.5 mm x 0.5mm), the MI is calculated as the total number of scratches divide d by the total number of pits. As a standard, an MI below 1.5 indicates a browsing diet a nd an MI above 1.5 indicates a grazing diet (MacFadden et al., 1999). Additional conclusions can be draw n by comparing the analyzed tooth to a database of the microwear of extant animal s with observed known diets. Plots of the number of pits versus the numbe r of scratches for these extant herbivores reveal distinct morphospaces indicative of browsing, gr azing, and mixed diets (Solounias and Semprebon, 2002). Microwear studies were initially conduc ted at high magnifi cation using Scanning Electron Microscopy (SEM) imagery (Grine, 1986). Recently, however, a lowmagnification technique was developed to redu ce the time and financial costs of the microwear method. Analyzing microwear at only 35x magnification has been shown to

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41 reveal the same results as high magn ification (Solounias and Semprebon, 2002). Solounias and Semprebon (2002) also created four additional quantifyi ng characters to attain a more detailed understa nding of dietary hab its. These characters can be used in hierarchical cluster analyses to determine wh ich kind of extant herbivores most closely resemble the fossil taxa in terms of microwea r, and therefore diet. However, microwear is subject to the Last Supper Effect, the lim itation of reflecting an individuals last few meals, rather than the life-history of diet (Grine, 1986). Therefore, microwear analyses are based on the assumption that the animals typical diet is reflected by these final meals. Materials and Methods Microwear analyses were conducted on th ree samples of the most hypsodont taxon from the WCF assemblage, Acritohippus isonesus Microwear analyses were conducted instead of mesowear because of the small sample size. The standard tooth position for microwear analysis is the second molar (upper or lower) (Solounias and Semprebon, 2002; Rivals and Deniaux, 2003). No other horses, such as Merychippus primus or Merychippus gunteri from the WCF were analyzed for microwear because there are not enough M2s for a statistical analysis. Due to the very limited sample size of the WCF, only one tooth of A isonesus (part of an associated dentition) was positively identified as a second molar (M2). The other two samples we re identified as first or second molars (M1/2s). Based on the curve of the mesostyle, it appears likely that both of these teeth are second molars, but it cannot be stated with certainty. Statistical analyses, such as the unpaired Students t-test and nonparametric Mann-Whitney test, were conducted on the collected results to determine whether ther e exist significant differences between the M1/2s and the one positively identified M2. Microwear analyses were also conducted on

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42 specimens of the hypsodont horse, Neohipparion trampasense from the Love Bone Bed site (~9.5 Ma) of north central Fl orida. These microwear results were used for comparison to A isonesus This study followed the procedure for microw ear analysis outlined in Solounias and Semprebon (2002). The first step is to clean th e occlusal surface of each tooth using 95% alcohol and cotton swabs. A mold is then made of the tooth using high-precision polyvinylsiloxane dental impression material. The mold is removed and discarded in order to remove any remaining debris from the enamel. A second mold is then made. After the second mold has hardened, it is used to make a clear high-quality epoxy cast (using a resin to hardener ratio of 5:1). Afte r 1 days, the cast has hardened and is ready for analysis. The standard for microwear analysis consis ts of looking at a 0.4 mm x 0.4 mm area of the cast under 35x magnification (Solounias and Semprebon, 2002). Those dimensions (0.4mm x 0.4mm) were used because the objective crosshairs had 0.4 mm increments at that magnification. It should be noted that the only stereo microscope with crosshairs available for this study had 50x magnifi cation, not 35x. Additionally, the crosshair increments had larger spacing, causing the sear ch area to be larger about 0.5mm x 0.5 mm. The increased magnification and search ar ea result in higher numbers of scratches and pits than would be found using the standard magnificat ion and search field. While this has no effect on the calculate d ratio of scratches to pits or on the percentages of other quantitative categories, the increase in averag e pit and scratch numbers prevents the use of hierarchical cluster analyses to asse ss dietary subcategories. However, these

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43 subcategories are not essential for this st udy, which is only concerned with whether the taxa were eating grass or browse. To observe the micowear features, a li ght source is shone through the cast at a shallow angle to the occlusal surface. Th e casts are analyzed in a dark room and adjustments to the intensity and angle of the light source are often made to best observe the microwear features. Two 0.5 mm x 0.5 mm areas were assessed for each tooth. Following Solounias and Semprebon (2002), thes e areas were located along the shear facet of the second enamel band on the par acone of each upper tooth. For lower teeth, the search areas were restricted to the shear facet on the protocone. Pits are defined as microscopic defects in the enamel that have a length:width ratio < 4, while scratches are defects that have a ratio 4 (Grine, 1986; Teaford and Robinson, 1987). These categories are obvious under low magnification. Pits usua lly appear as fairly round dots with a length:width ratio of about 1 or 2, while scra tches are always much longer and typically have length:width ratios much higher than 4. For each tooth, the pit and scratch numbers from the two search areas are averaged. Pits ar e further classified as large or small. Small pits are the most numerous type and are fair ly rounded. There are usually a few pits that are at least twice the diameter of the small pits. These are categori zed as large pits and appear deeper and dark due to less refraction. Scratches ar e subdivided into fine or coarse. Fine scratches are the narrowest scra tches. They are shallow and often are white from light reflection. Coarse scra tches are often dark and longer than most fine scratches. It is also noted when a sample bears more th an four cross scratches. Cross scratches are any scratches that run roughly perpendicular to the majority of scratches. Finally, the average microwear index for each taxon is calculated.

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44 Results The observed counts of microwear features fo r each specimen are recorded in Table 4-1 and the calculated MI and percentages are presented in Table 42. Table 4-1 follows the format and uses some of the quantita tive parameters established by Solounias and Semprebon (2002). The average number of pits and scratches for each taxon is listed, followed by the microwear index (the ratio of scratches to pits), and two of the newer quantitative variables. Since the microscope fi eld used in this study is not the commonly used size, these variables cannot be utilized in cluster analys es to determine more detailed similarities to the diets of extant mammals. However, these variables are helpful in making general inferences. The listed percentage s in Table 4-2 for each of these attributes refer to the percentages of specimens th at bear that corresponding attribute. Unpaired Students t-tests and nonparametric Mann-Whitney tests were used to examine the concordance of the three A isonesus specimens. The MIs of the two dubiously identified teeth (U F 223080 and UF 223081) were compared to the MI of the positively identified M2 (UF 223063). The Stude nts t-test and Mann-Whitney p-values for comparing UF 223080 UF 2230 63 are 0.6826 and 0.4386, respectively. The Students t-test and Mann-Whitney p-values for comparing UF 223081 to UF 223063 are 0.2195 and 0.1213, respectively. For both of the M1/2 specimens, the Mann-Whitney test and Students t-test yield p-valu es greater than 0.05 and reve al no significant differences between the MIs. For each sample of both A isonesus and N trampasense the average number of scratches is almost double the av erage number of pits. The average MIs for A isonesus and N trampasense are 1.97 and 1.98, respectively. The MIs of A isonesus and N trampasense were compared for statistical differenc es using an unpaired Students t-test and nonparametric Mann-Whitney test. The pvalues for the Students t-test and Mann-

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45 Whitney test are 0.5707 and 0.8690, respectively. These p-values are greater than 0.05 and show that the MIs of A isonesus and N trampasense are not statistically distinct. Additionally, all of the samples for both taxa had scratches that were predominantly fine. Each sample also had at l east four cross scratches.

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46 Table 4-1. Individual microwear counts for 3 specimens of Acritohippus isonesus and 7 specimens of Neohipparion trampasense Each specimen has two areas (A and B) assessed for microwear. Abbreviations: UF ID = catalogue number in the Florida Museum of Natural History collections, # x-scratches = number of cross-scratches. Taxon UF ID # pits# scratches # x-scratches # fine scratches # coarse scratches Acritohippus 223063A 22 86 39 83 3 isonesus 223063B 43 96 20 81 15 223080A 17 58 16 53 5 223080B 37 57 10 53 4 223081A 83 118 27 110 8 223081B 65 111 40 106 5 Neohipparion 27991A 29 70 15 62 8 trampasense 27991B 42 48 13 45 3 27992A 45 59 26 55 6 27992B 22 57 17 52 5 27993A 11 34 18 28 6 27993B 23 39 5 35 4 32280A 68 103 31 98 5 32280B 42 76 16 67 9 32291A 25 49 9 48 1 32291B 24 85 25 79 6 36287A 29 58 26 53 5 36287B 30 69 25 58 11 32114A 37 103 17 99 4 32114B 32 60 18 54 6

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47 Table 4-2. Calculated average micr owear values and percentages for Acritohippus isonesus and Neohipparion trampasense Abbreviations: N = sample size, Avg. # pits = the average number of pits for the sample population, Avg. # scratches = the average number of sc ratches for the sample population, MI = microwear index, % Fine scratches = th e percentage of the sample population that possess scratches that are predomin antly fine, % coarse scratches = the percentage of the sample population that possess scratches that are predominantly coarse, % cross scratches = the percentage of the sample population that exhibits at least 4 cross scratches. Taxon N Avg. # pits Avg. # scratches MI % Fine scratches % Coarse scratches % Cross scratches A. isonesus 3 44.5 87.67 1.97100 0 100 N. trampasense 7 32.79 65 1.98100 0 100 Table 4-3. Isotopic data for e quids from 4 central Florida sites. Abbreviations: UF ID = catalogue number in Florida Museum of Natural History collections. (Modified from MacFadden and Cerling, 1996) Taxon Site UF ID Material 13C() 9.5 Ma Level, late Clarendonian, late Miocene Neohipparion trampasense Love Bone Bed 32230 R. P3-M3 -11.6 Cormohipparion plicatile Love Bone Bed 32265 R. P2 -12.6 Cormohipparion plicatile Love Bone Bed 32265 R. P3 -12.5 Cormohipparion plicatile Love Bone Bed 32265 R. P4 -11.0 Cormohipparion plicatile Love Bone Bed 32265 R. M1 -12.0 Cormohipparion ingenuum Love Bone Bed 60396 R. P2 -10.8 Cormohipparion ingenuum Love Bone Bed 35979 R. P2 -10.8 7.0 Ma level, "middle" Hemphillian, late Miocene Nannippus aztecus Moss Acres 69933 R. M3 -7.9 cf. Nannippus Moss Acres None R. p2 -5.3 4.5 Ma level, latest Hemphillian, early Pliocene Nannippus Upper Bone Valley None L. M -6.0 Nannippus aztecus Upper Bone Valley 63633 L. M2 -9.1 Nannippus aztecus Upper Bone Valley 65796 R. M1 -2.4 1.5 Ma level, early Irving tonian, early Pleistocene Equus "leidyi" Leisey 1A 80047 R. M3 -1.5 Equus "leidyi" Leisey 1A None R. P2 -3.5

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48 CHAPTER 5 STABLE ISOTOPE ANALYSIS Background Plants utilize three different types of metabolic pathways to process and use carbon. These pathways are: the C4 pathway (or Hatch-Slack cycle), the C3 photosynthetic pathway (the Calvin cycle), and the CA M (Crassulacean acid metabolism) pathway (Bender, 1971). The C4-dicarboxylic acid pathway utilizes CO2 through carboxylation of phosphoenolpyruvate (OLeary, 1988). Th e Calvin Cycle, used by C3 plants, uses the enzyme ribulose biphosphate carboxylase to fix CO2 (OLeary, 1988). The CAM pathway also uses ribulose biphos phate carboxylase to take in CO2, but the process is more similar to what happens in the bundle shea th cells of C4 plants (OLeary, 1988). Plants that use the C4 pathway are primarily tropical grasse s, but also include some fruits and vegetables (OLeary, 1988). C3 plants include trees, shrubs, and cool-climate grasses, and dicots (OLeary, 1988). The CAM plants consist primarily of desert succulents (OLeary, 1988). Each plant metabolic pathway results in the isotopic fractionati on of carbon (Figure 5-1) as it is taken into the plant cells from CO2 (Bender, 1971). The heavier carbon isotope, 13C, is discriminated against to varyi ng degrees dependent on the pathway used, and the 13C/12C isotopic ratios of plants decreases re lative to atmospheri c isotopic ratios (Bender, 1971). The lighter isotope is preferentially us ed due to the physical and chemical properties associated with its mass (OLeary, 1988). The carbon isotopic ratio

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49 ( 13C) is represented as the parts per thousand difference between the sample and a standard, the Peedee Belemnite from South Carolina (Craig, 1957). C3 plants have an average 13C value of -27.1 2.0 and a range from about -35 to -22, while C4 plants have an average 13C value of -13.1 1.2 and have a more limited range from -14 to -10 (OL eary, 1988). CAM plants have a range of -10 to -20 that distinguishes them from C3 plants, but not C4 plants (O Leary, 1988). Since CAM plants are known to be dominant only in xeric habitats (Ehleringer et al., 1991), they are typically not cons idered in paleodiet analyses of temperate or subtropical paleoenvironments. When mammalian herbivores consume pl ants, the carbon isotopes are fractionated once again. By determining the fractionati on factor for the mammal in question, the carbon isotopic signature can be used to determine the diet, in terms of C3 and C4 consumption, of the herbivore. Stable car bon isotope analyses were first used in archaeology to determine th e paleodiets of ancient human populations (MacFadden and Cerling, 1996). These studies analyzed the inorganic apatite in bone, which exists primarily as hydroxyapatite, or Ca10(PO4)6(OH)2 (Hillson, 1986; Wang and Cerling, 1994; MacFadden and Cerling, 1996). Trace amounts of carbon are present in this mineral when it is commonly altered during skeletal formation, with carbonate (CO3)-2 replacing phosphate to yield Ca10(PO4,CO3)6(OH)2 (Hillson, 1986; Newesely, 1989; McClellan and Kauwenbergh, 1990). Due to th e porous nature of bone collagen, the hydroxyapatite with structural carbonate is ex tremely susceptible to diagenetic alteration (Quade et al., 1992). Dental enamel, however, is much more resistant to diagenesis because it is has very low porosity and is mo re than 96% inorganic by weight (Quade et

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50 al., 1992; Wang and Cerling, 1994). Additionally, enamel is more than 95% hydroxyapatite (Hillson, 1986). Multiple studies have found that the biogenic apatite of enamel does not undergo diagenesis in most depositional situations and therefore retains primary isotopic values (Quade et al., 1992; Wang and Cerling, 1994). Cerling and Harris (1999) determined an enrichment factor of +14.1 0.5 between the 13C of the plants consumed and the bi oapatite in the enamel of extant ruminant mammals. This consistent enrichme nt establishes distin ct ranges of isotope ratios for ruminants that consume C4 or C3 plants. Grazers (animals that feed primarily on C4 grasses) fall in a range of 0 to +4 wh ile browsers (animals that feed off of leaves from C3 shrubs and trees) fall w ithin a range of -21 to -8 (Cerling and Harris, 1999). Stable carbon isotope analyses can ther efore be conducted on ruminant teeth to determine diet. This method has been extended to extinct ruminants to determine a general classification of feedi ng habit. To do this, paleodietar y analyses have adopted the categories used to describe extant herb ivores, established by Hofmann and Stewart (1972). There are three genera l categories: concentrate selectors (browsers), bulk and roughage feeders (grazers), and intermediate feeders (mixed feeders that consume both browse and grass) (Hofmann and Stewart, 1972). These categories have been subdivided further to detail the complexity of the f eeding strategy. These subdivisions, however, are rarely used in paleodiet analyses because it is difficult to calculate percentages of plant type for an extinct animal. It is also impor tant to recognize that paleodiet studies that utilize stable isotope analyses rely on two assumptions: 1) Th e metabolic pathways of the plants behaved similarly in the past as they do today (i.e., fractionated to the same

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51 degree), and 2) the metabolic pathways and en richment factor of ruminant mammals have been consistent throughout time. There is another factor that must be corrected when analyzing stable carbon isotopes in fossils. As stated above, the 13C values of modern ruminants are derived from the fractionation of carbon from plant inta ke, which is fractionated from the fixation from atmospheric CO2. Atmospheric 13C values have decreased from approximately -6.5 to approximately -8.0 over the course of the last 200 years, due to the burning of fossil fuels (Friedli, Ltscher, Oeschger, Siegenthaler, and Stau ffer, B, 1986; Marino, McElroy, Salawitch, and Spaulding, 1992). Du e to this change in atmospheric 13C values, fossil bioapatite values are about 0.5 to 1.3 more positive than the values of modern mammals (Koch, Hoppe, and Webb, 1998). This adjustment shifts the endmembers on the scale for paleodiet interp retation: a diet strictly consisting of C3 plants would be no more positive than -8.7 and a pure C4 diet would be no more negative than -0.5 (Feranec, 2003). Using these endmem bers, a browser (less then 10% C4 intake) would have a 13C value less than -7.9, a grazer (less than 10% C3 intake) would have a 13C value greater than -1.3, and a mixed feeder would have a 13C value between -7.9 and -1.3 (Feranec, 2003). In addition to the utility of 13C values, valuable dietary and environmental information can also be attained from the 18O values of structural carbonate and phosphate in enamel. Several studi es have determined that the 18O of a mammals body water is directly correlated to the 18O of ingested water from drinking water and food, such as plants (Luz, Kolodny, and Horowitz, 1984; Luz and Kolodny, 1985; Bryant and Froelich, 1995; Bryant, Froeli ch, Showers, and Genna, 1996a; Kohn, 1996). Furthermore,

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52 these 18O values are recorded in the structur al carbonate and phosphate of mammalian tooth enamel, which mineralizes in isotopi c equilibrium with body water (Longinelli, 1984; Luz et al., 1984). This conclusion has been corroborated by the calculation of a consistent fractionation factor for oxygen be tween body water and structural carbonate in modern equids (Bryant, Koch, Froelich, Showers, and Genna, 1996). Therefore, the 18O values of mammals can be used to determine the 18O values of their water source. However, it must first be determined whether that particular mammal obtains most of its body water from plants or drinking water. For obligate drinkers, tooth enamel can reflect the 18O values of meteoric water. The 18O values of precipitation are contro lled by temperature (Dansgaard, 1964). Typically, this link causes the 18O values of meteoric water to be enriched during periods of warm weather and depleted dur ing periods of cool weather (McCrea, 1950; Bryant et al., 1996a). The 18O values of meteoric water can therefore be used to interpret seasonality. As menti oned previously, the 18O values of water sources are reflected in the carbonate and phosphate of mammalian toot h enamel (Longinelli, 1984; Luz et al., 1984). However, the metabolic rate of the mammal can influence the 18O values recorded in the enamel (Bryant and Froe lich, 1995; Kohn, 1996; Kohn, Schoeninger, and Valley, 1998; Zhow and Zheng, 2002). This poses a problem for using small mammals as environmental indicators, but Bryant and Froelich (1995) note that because the proportion of oxygen taken up as liquid wate r increases while the food requirement decreases, the proportion of surficial drinking water reflected in [ 18O of body water] will increase with increasing body size. The 18O of surface water will then be reflected in the enamel phosphate and carbonate of large ma mmals that weigh more than 1 kg (Bryant

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53 and Froelich, 1995). The use of 18O values from tooth enamel as environmental indicators has been extended to fossils, where the variation of 18O values of enamel phosphate along serially sampled teeth from Miocene horses (Bryant et al., 1996a) and Holocene bison and sheep (Gadbury, Todd, Jahren, and Amundson, 2000) has been determined to reflect seasonality. Simila r studies have been conducted using the structural carbonate in tooth enamel (Cer ling and Sharp, 1996; Higgins and MacFadden, 2004; MacFadden and Higgins, 2004). Therefore, along the serially sampled tooth of an obligate drinker, more positive (or enriched) 18O values will indicate summer and more negative (or depleted) values will indicate wi nter (Fricke and ONe il, 1996; Feranec and MacFadden, 2000). For herbivores that are not obligate drinkers, the 18O of structural carbonate in fossil teeth reflects the 18O of the water in consumed leaves (Longinelli, 1984; Bryant, Froehlich, Showers, and Genna, 1996; Koch, 1998). The 18O of water in plants is influenced by temperature, and humidity (Dongman, Nrnberg, Frstel, and Wagener, 1974; Epstein, Thompson, and Yapp, 1977; St ernberg, Mulkey, and Wright, 1989). Due to this relationship, evapotra nspiration causes leaves in forest canopies and dry, open habitats to have higher 18O values than ground-level leav es in cool, humid forests (Frstel, 1978; Kohn, Schoeninge r, and Valley, 1996; Cerling, Harris, Ambrose, Leakey, and Solounias, 1997a). These values can be en riched by more than 20 compared to the 18O of local precipitation (Fr stel, 1978; Kohn et al., 1996). For non-obligate drinkers, the 18O of structural carbonate can yield some general information about the mammals habitat (e.g., arid, open areas versus cool forests), but it does not accurately reflect seasonality.

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54 Materials and Methods The assemblage of eight ungulates anal yzed ranges from expected browsers (brachydont dentitions found in the unidentifi ed artiodactyl, oreodont, one rhinocerotid, and one equid) to expected mixed feed ers/grazers (mesodont to hypsodont dentitions found in three equids and one rhinocerotid). Due to the er uption order of teeth and the weaning stage of mammals, the tooth positions most appropriate for a post-nursing diet analysis are the third premolar (P3), fourth premolar (P4), and third molar (M3) (Bryant et al., 1996a; Fricke and ONeil, 1996; Hoppe, Stover, Pascoe, and Amundson, 2004). Other teeth were analyzed for taxa that lacked any positively identified P3s, P4s, or M3s. These taxa include Anchitherium clarencei, Teleoceras and Aphelops In all, twenty-four teeth were selected for bulk stable car bon and oxygen isotope analysis of enamel carbonate (Table 5-1). Bulk samples, taken along the entire height of the tooth, yield an average stable isotopic ratio for the time during which the enamel mineralized. Six specimens, two from three different taxa, were also chosen for serial sampling to obtain isotopic ratios with finer reso lution. The taxa chosen were: Aphelops sp., the brachydont, long-limbed rhinocerotid e xpected to be an open-c ountry cursorial browser; Merychippus primus a hypsodont horse presumed to be a mixed feeder; and Acritohippus isonesus the most hypsodont taxon from the assemblage that is expected to be a grazing horse. Serial samples of bioapatite were taken from 6 teeth at 5-millimeter intervals along the length of each tooth. Serial stable isotope analyses were conducted in order to analyze the variation of diet for an individual. Since a tooth minera lizes from the crown to the base over the course of a few months to two years (Hillson, 1986), serial samples reveal a dietary interpretation from a smaller time interval than a bulk sample. However, the isotopic signals are masked due to the sligh tly non-perpendicular mineralization of tooth

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55 enamel (Passey and Cerling, 2002). Despite this effect, the serial sa mples still yield an isotopic ratio that is averaged over shorter time intervals th an a bulk sample and allows some variation to be discerned (MacFadden and Higgins, 2004). For the purposes of this study, it is important to show any C4 dietary influences throughout the mineralization stage of the animal. The sampling and preparation procedures fo r stable isotope anal ysis are comprised of two main components: 1) physical sampling and 2) chemical processing. The physical sampling consists of the actual removal of enamel for analysis and the chemical processing is the procedural treatment of the enamel to remove organic compounds and all other contaminants that will affect the stable isotope signatur e. The physical sampling begins by identifying any enamel flakes on the tooth that appear plia ble. The surface of the flake is cleaned using brushes, and then re moved. A drill is then used to remove any dentine remaining on the inside surface of the fl ake. It is then ground in a clean mortar and pestle, and the enamel powder is placed in a labeled microcentrifuge vial. If there are no flakes apparent, then a part of the tooth must be drilled, pr eferably where the enamel is thick. The surface is prepared by cleaning it w ith carbide dental drill bits and brushes. All the cementum and soil must be removed from the tooth to avoid contaminating the sample. Once the surface is cleaned, a Foredom drill is used at low RPMs to remove approximately 5 milligrams of pristine enamel. The drill operator must be careful not drill into the dentine, as dentine has a different 13C value from enamel and will contaminate the sample. Bulk samples were taken along the entire he ight of the tooth, while serial samples were taken at 5-millimet er increments starting at the base of the

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56 tooth. All the enamel powder is collected on weighing paper and pl aced into a labeled microcentrifuge vial. The first step in the chemical treatment of the enamel samples is to remove all organic material that might affect the car bon isotope ratio. To do this, 1 mL of 30% H2O2 is added to each sample. Then, the vial s are closed and shaken on a Thermolyne Type 16700 Mixer in order to thoroughly mix th e enamel powder with the H2O2. The samples are then placed, with the lids off, in a reaction cabinet overnight. After approximately 24 hours, some of the samp les may still be reacting with the H2O2, indicating the presence of abundant organic residues. The samples are all treated a second time with H2O2 to remove these organic materials. After the second H2O2 treatment, the samples are centrifuged and the H2O2 is removed. One milliliter of distilled water is added to each vial and then mixed. The samples are centrifuged, and the water is remove d using a pipetter. Th is rinsing step is repeated two more times. After the third rins e, 1 mL of 0.1 M acetic acid is added to the vials to remove carbonates from the samples. The samples are shaken and left in the reaction cabinet overnight. The samples are not allowe d to react with the acetic acid for more than 24 hours, since it has been show n that prolonged exposur e to acetic acid can affect the carbon isotope signatures (LeeThorpe, Sealy, and van der Merwe, 1989; Vennemann, Hegner, Cliff, and Benz, 2001). The next day, the samples are centrifuged a nd the acetic acid is removed. Distilled water is used to rinse the samples three more times. After the rinses, 95% methanol is added to each sample to remove water. Again, the samples are shaken to mix the

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57 methanol with the enamel, and then the meth anol is removed. Finally, the samples are placed in the reaction cabinet to dry overnight. After the samples have dried, they are analyzed using a VG Prism mass spectrometer at the Department of Geological Sciences at the University of Florida. Approximately 1 mg of each sample is placed in a small sample boat and loaded into the mass spectrometer, accompanied by standards. The bulk samples are standardized to either the MEme (MacFadden Elephantus maximus enamel, 13C = -10.43) or the NBS-19 ( 13C = +1.95; Coplen, 1996) standard to ensure the precision of the results and the calibration of the mass spectrometer. A ll of the serial samples are calibrated to the NBS-19 standard. All of the measured is otopic values are then calibrated to the universal V-PDB (Vienna Pee Dee Belemnite). The values are presented in standard -notation: 13C or 18O = [(Rsample/RV-PDB) 1] 1000, where Rsample is the measured 13C/12C or 18O/16O ratio of the sample. The analytical precision of samples run with the MEme standard is 0.05 and 0.07 for 13C and 18O, respectively. The analytical precision of samples run with the NBS-19 standard is 0.09 and 0.18 for 13C and 18O, respectively. The analytical precision is m easured by calculating one standard deviation of the corrected 13C and 18O values of the standards. Results The bulk 13C values for all the sampled specimens range from -11.39 to -8.30 (Table 5-2, Table 5-3, Figure 5-2). The most positive mean bulk 13C value belongs to Aphelops sp. and the most negative belongs to Teleoceras sp., although Teleoceras has a sample size of only one. The bulk 18O values for all the sampled specimens range from -2.15 to 2.71 (Table 5-3, Figure 5-2).

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58 Three taxa were selected for serial sampling: one expected browser with brachydont dentition ( Aphelops sp.) and two expected grazing /mixed feeding horses with hypsodont dentitions ( Merychippus primus and Acritohippus isonesus ). Individual serial stable isotope values ar e presented in Appendix B. The serial stable isotope samples for the first specimen of Aphelops (UF 116827) range from -8.37 to -11.72 for carbon and from -1.99 to -0.31 for oxygen. (Table 5-3, Figures 5-3 and 5-4). The second specimen (UF 104227) has a narrower range of -9.76 to -10.73 for carbon and a much wider and more positive range of 0.71 to 3.46 for oxygen (Table 5-3, Figures 5-3 and 5-4). For Merychippus primus the serial 13C values range from -9.26 to -10.54 (UF 221419) and from -9.39 to -9.72 (UF 221427) and the serial 18O values range from 0.15 to 1.99 (UF 221419) and from 1.12 to 2.83 (UF 221427) (Table 5-3, Figures 5-5 and 5-6). Acritohippus isonesus exhibits serial 13C ranges of -9.92 to -10.66 (UF 221407) and -10.33 to -11.96 (UF 217590) as well as serial 18O ranges of 0.25 to 2.56 (UF 221407) and 0.62 to 2.37 (UF 217590) (Table 5-3, Figures 5-7 and 5-8).

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59 Figure 5-1. Schematic of isotopic fracti onation between atmospheric carbon and C3 plants, as well as fractionation between C3 plants and ruminant herbivores. 13C values are listed in parentheses. The average 13C value for C3 plants is approximately -27.1 and the average 13C value for C3-consuming ruminants is approximately -13. The average isotopic fractionation between atmospheric carbon and C3 plants is a depletion of about -19.5. The isotopic fractionation between plants and ruminant s is an enrichment of approximately 14.1. (Modified with permission from Koch et al., 1992)

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60 Table 5-1. List of the 24 specimens an alyzed for stable ca rbon and oxygen isotope analysis. Specimens are representati ves of the Willacoochee Creek Fauna from the early Barstovian (middle Miocene) Dogtown Member of the Torreya Formation. Abbreviations: UF ID = cat alogue number in the Florida Museum of Natural History collections, ELC = Englehard La Camelia Mine, LC2 = La Camelia 2, and MGF = Milwhite Gunn Farm Mine. UF ID Taxon Crown Height Tooth Site 221429 Teleoceras sp. Brachydont R. I ELC 104227 Aphelops sp. Brachydont Tooth fragment MGF 116827 Aphelops sp. Brachydont R. MX fragment ELC 217565 cf. Aphelops Brachydont L. PX LC2 114723 Anchitherium clarencei Brachydont L. P2 ELC 221402 Anchitherium clarencei Brachydont R. M1 ELC 217590 Acritohippus isonesus Hypsodont L. P4 LC2 217562 Acritohippus isonesus Hypsodont R. M3 LC2 221405 Acritohippus isonesus Hypsodont L. M3 ELC 221407 cf. Acritohippus isonesus Hypsodont R. P3/4 ELC 114721 Merychippus gunteri Mesodont R. M3 ELC 116829 Merychippus gunteri Mesodont L. P3/4 ELC 221416 Merychippus gunteri Mesodont L. P3/4 ELC 221408 Merychippus gunteri Mesodont L. M3 ELC 114976 Merychippus primus Mesodont R. P3/4 ELC 104208 Merychippus primus Mesodont L. P3/4 MGF 221415 Merychippus primus Mesodont R. P3 ELC 221419 Merychippus primus Mesodont L. P4 ELC 221426 Merychippus primus Mesodont R. M3 ELC 221427 Merychippus primus Mesodont R. M3 ELC 221428 Merychippus primus Mesodont R. M3 ELC 221418 Merychippus primus Mesodont R. M3 ELC 116823 Ticholeptus hypsodus Brachydont R. M3 ELC 221434 Artiodactyla Brachydont R. M3 ELC

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61 Table 5-2. Bulk stable carbon and oxygen isot ope values for Willacoochee Creek Fauna. Abbreviations: UF ID = catalogue number in Florida Museum of Natural History collections, Unident. = unidentified tooth position, ELC = Englehard La Camelia Mine, MGF = Milwhite G unn Farm Mine, and LC2 = La Camelia 2 Mine. UF ID Taxon 13C () 18O () Tooth Site 221429 Teleoceras sp. -11.39 -0.41 R. I ELC 104227 Aphelops sp. -9.48 1.01 Unident. MGF 116827 Aphelops sp. -8.72 -2.15 R. MX ELC 217565 cf. Aphelops -10.23 0.38 L. PX LC2 114723 Anchitherium clarencei -8.90 2.32 L. P2 ELC 221402 Anchitherium clarencei -10.23 1.45 R. M1 ELC 217590 Acritohippus isonesus -10.87 2.03 L. P4 LC2 217562 Acritohippus isonesus -11.00 -0.35 R. M3 LC2 221405 Acritohippus isonesus -9.67 1.95 L. M3 ELC 221407 cf. Acritohippus isonesus -10.16 1.02 R. P3/4 ELC 114721 Merychippus gunteri -11.09 -0.65 R. M3 ELC 116829 Merychippus gunteri -8.30 -0.16 L. P3/4 ELC 221416 Merychippus gunteri -9.72 1.86 L. P3/4 ELC 221408 Merychippus gunteri -11.19 0.67 L. M3 ELC 114976 Merychippus primus -8.78 1.36 R. P3/4 ELC 104208 Merychippus primus -9.54 -0.82 L. P3/4 MGF 221415 Merychippus primus -8.79 2.10 R. P3 ELC 221419 Merychippus primus -10.00 0.85 L. P4 ELC 221426 Merychippus primus -9.76 1.14 R. M3 ELC 221427 Merychippus primus -8.70 1.03 R. M3 ELC 221428 Merychippus primus -9.73 0.45 R. M3 ELC 221418 Merychippus primus -9.50 0.97 R. M3 ELC 116823 Ticholeptus hypsodus -9.83 0.33 R. M3 ELC 221434 Artiodactyla -10.87 0.66 R. M3 ELC

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62 Table 5-3. Descriptive statistics of the 13C and 18O values for 8 herbivores from the Willacoochee Creek Fauna. Abbrevia tions: Unident. = unidentified, N = sample size, SD = standard deviation. Bulk Sampling Taxon N 13C () 18O () Mean SD Range Mean SD Range Anchitherium clarencei 2 -9.57 0.94 -10.23 to -8.90 1.89 0.94 1.45 to 2.32 Merychippus primus 8 -9.35 0.51 -10.39 to -8.70 0.89 0.84 -0.82 to 2.10 Merychippus gunteri 4 -10.08 1.36 -11.19 to -8.30 0.43 1.10 -0.65 to 1.86 Acritohippus isonesus 5 -10.43 0.62 -11.00 to -9.67 1.16 1.11 -0.35 to 2.03 Teleoceras sp. 1 -11.40 -0.41 Aphelops sp. 3 -9.48 0.76 -10.23 to -8.72 -0.25 1.67 -2.15 to 1.01 Ticholeptus hypsodus 1 -9.83 0.33 Unident. artiodactyl 1 -10.87 0.66 Serial Sampling Taxon N 13C () 18O () Mean SD Range Mean Range Aphelops sp. 19 -10.52 0.82 -10.23 to -8.72 0.06 -1.99 to 3.46 Merychippus primus 9 -9.67 0.43 -10.39 to -8.70 1.66 0.15 to 2.90 Acritohippus isonesus 12 -10.66 0.65 -11.19 to -8.30 1.51 0.25 to 2.56

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63 Figure 5-2. Plot of bulk 13C vs. 18O values for the 8 herbivores from the Willacooc hee Creek Fauna. Note that all the herbivores bear bulk 13C values below -8.30 and most speci mens cluster between -9.50 and -10.50.

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64 Figure 5-3. 13C values for serial samples of two Aphelops specimens. Note that all the values are lower than -8.37 Position along tooth refers to the distance from the base of the tooth. Figure 5-4. 18O values for serial samples of two Aphelops specimens. Note that both specimens exhibit variation outside of th e range of error. Position along tooth refers to the distance from the base of the tooth.

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65 Figure 5-5. 13C values for serial samples of two Merychippus primus specimens. Note that all the values are lower than -9 .26. Position along tooth refers to the distance from the base of the tooth. Figure 5-6. 18O values for serial samples of two Merychippus primus specimens. Note that both specimens exhib it variation outside of the range of error. Position along tooth refers to the distan ce from the base of the tooth.

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66 Figure 5-7. 13C values for serial samples of two Acriohippus isonesus specimens. Note that all the values are lower than -9.92. Position along tooth refers to the distance from the base of the tooth. Figure 5-8. 18O values for serial sampling of two Acritohippus isonesus specimens. Note that both specimens exhibit variat ion outside of the range of error. Position along tooth refers to the di stance from the base of the tooth.

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67 CHAPTER 6 DISCUSSION Of the eight taxa analyzed from the W illacoochee Creek Fauna (WCF), three are expected to yield significant proport ions of browse in their diets: Anchitherium clarencei Ticholeptus hypsodus and Aphelops A clarencei is a three-toed horse with low-crowned cheek teeth and stocky limbs suggestive of a br owse diet in a woodla nd habitat (Janis et al., 2002). The only positively identifi ed artiodactyl from the WCF, T hypsodus has a mesodont dentition and is expected to be a mixed feeder (Lander, 1998). Aphelops is a hornless, brachydont aceratherine rhino with l ong limbs suggestive of a cursorial habit (Matthew, 1932; Janis, 1982). Aphelops is traditionally described as an open-country browser, with the extant black rhino ( Diceros bicornis ) cited as a modern analog (Matthew, 1932). Furthermore, Janis (1982) described all acerat herine rhinos as browsers within woodland savannas. There has been some variance on the dietar y classification of Aphelops Webb (1983) recognized Aphelops and Teleoceras as grazers from the Clarendonian Chronofauna, the succession of Barsto vian-Clarendonian grazers. However, stable isotopic analyses of Aphelops specimens from multiple Florida localities (ranging from 9.5 to 4.5 Ma), combined w ith crown-height data, suggest that Aphelops was eating C3 browse material before and after the ~7 Ma spread of C4 grasses (MacFadden, 1998). The WCF Aphelops specimens are approximately 6 million years older than the previously analyzed sp ecimens, but the dental and postcranial morphologies still suggest a diet of C3 browse.

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68 Teleoceras is a moderately hypsodont teleoceratine rhino with short limbs. It has been traditionally interpreted as semi-a quatic grazer, comparable to the extant hippopotamus, Hippopotamus amphibious (Scott, 1937; Voorhies, 1981; Webb, 1983; Prothero, 1992). Matthew (1932) rejected the hypothesis of a semi-aquatic habitat for Teleoceras and instead suggested that the rhino grazed on grassy plains. Voorhies and Thomasson (1979) determined that Teleoceras was a grazer, based on the presence of grass anthoecia in the oral a nd body cavities of specimens from the Ashfall Fossil Beds in Nebraska (10 Ma). They were, however, unable to determine whether that grass originated from mesic or lacustrine envi ronments. Recent isotopic evidence, however, has revealed that: 1) Teleoceras was, based on 18O values, not primarily aquatic; and 2) Teleoceras was a mixed feeder, consumi ng significant portions of C3 grass prior to the 7 Ma spread of C4 grasses and then shifting to a diet of C4 grasses after 7 Ma (MacFadden, 1998). This interpretation likens Teleoceras to the extant white rhino ( Ceratotherium simum ), a grazer (MacFadden, 1998). Base d on this interpretation of Teleoceras the specimens from the WCF would be expected to have 13C signatures indicative of a mixed diet, possibly composed of C3 grasses. The remaining equids from the WCF are all hypsodont three-toed horses. The hypsodont teeth of Merychippus primus and Merychippus gunteri suggest a grazing/mixed diet for these equids. Janis ( 1988) points out that, de spite fairly hypsodont cheek teeth, the Merychippus dentition is more similar to that of extant mixed feeders than to grazers. Whether Merychippus was a grazer or mixed feeder, the tooth morphology suggests that there is at least some grazing component to the animals diet.

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69 Acritohippus isonesus the most hypsodont taxon of the WC F, would be expected to be a grazer. Based on average bulk stable carbon isotope values, all eight taxa from the WCF fell within the range of a C3dominated diet, between -21 and -8 (Cerling and Harris, 1999). Additionally, only one sample had a 13C value more positive than -8.7 (a Merychippus gunteri specimen had a value of -8.30), in dicating that nearly the entire WCF community was consuming strictly C3 plants, according to the pre-industrial ranges of Feranec (2003). Even the most positive value was still more negative than -7.9, indicating that the animal was eating less than 10% C4 grass. However, atmospheric 13C values during the middle Miocene were considerably higher than during the pre-i ndustrial Holocene (Vincent a nd Berger, 1985). During the Monterey Excursion, from 16.5 Ma to 13.5 Ma, 13C values of benthic foraminifera were as high as +2.2, indicative of higher atmospheric 13C (Zachos et al., 2001). The higher atmospheric 13C would raise the 13C of plants, slightly raising the 13C of the enamel of mammals that consume the plants. This in crease would be no gr eater than about 1. Taking this enrichment into account, the 13C signatures of all the samples are well within a pure C3 diet. This suggests that each ung ulate was either grazing on C3 grasses or browsing, and not consuming any significant amounts of C4 grass. The serial sampling of Aphelops sp., Merychippus primus and Acritohippus isonesus also reveal no significant C4 fluctuations in diet at any point duri ng the mineralization of the enamel. For both Aphelops sp. and Merychippus primus the most enriched serial sample was not greater than -8.7, indicating a pure C3 diet. Once again, when the higher atmospheric 13C is considered, the serial samples fall well within the range of a pure C3 diet.

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70 The stable carbon isotope analyses suppor t the browser interpretations based on dental morphologies for A clarencei T hypsodus and Aphelops Conversely, the dentitions and lack of a C4 signal for Teleoceras and the three hypsodont equids suggest that they were consuming C3 grasses. Unfortunately, the sample sizes of M primus M gunteri and Teleoceras are inadequate for further inve stigation of grass consumption (e.g., microwear or mesowear analyses). Li kewise, the sample sizes of the suspected browsers are also insufficient for direct confirmation of a browse-dominated diet. A isonesus however, can be assessed for evid ence of a grass diet through microwear analysis. While conducting the microwear analyses, there was some doubt as to whether two of the A isonesus molars were M2s. However, since the parametric and nonparametric statistical tests found no signi ficant differences between the microwear indices (MI) of each A isonesus specimen, they are accepted he re as all being M2 teeth. The average microwear index (MI) for A isonesus is 1.97, well above the 1.5 threshold for grazers (MacFadden et al., 1999). The MI for N trampasense is 1.98, which is also significantly higher than 1.5. Th is supports the mesowear an alysis, which classifies N trampasense as a grazer. The MI of A. isonesus is not statistically different from that of N trampasense. The relatively high MI of A. isonesus coupled with the lack of a significant difference to the MI from the grazing N trampasense suggests that A isonesus was also dominantly a grazer, with no significant brow se component. The 13C data and microwear index indicate that A isonesus was a C3 grazer (Figure 6-1). This conclusion is supported by the scratch mor phology. The quantified scratches in extant grazers have indicated that a prevalence of fine scratches are observed in consumers of C3

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71 grasses, while coarse scratches dominate the enamel wear of C4 grazers (Solounias and Semprebon, 2002). For each sample of A. isonesus fine scratches composed at least 84% of the total number of scratches. Further paleoecological interpretations can be made from the bulk and serial 13C values of the WCF. In closed canopy forests, CO2 becomes trapped near the forest floor, elevating the CO2 concentration near the forest fl oor and in turn depleting the 13C of that air which, in turn, results in the depletion of 13C in plant tissues (Medina and Minchin, 1980; Medina, Montes, Cuevas, and Rokzandic, 1986; van der Merwe and Medina, 1989; Cerling et al., 1997a). Further depletion of 13C in plant tissues results from the lack of light reaching the forest floor, caused by the dense cover of the canopy (Medina and Minchin, 1980; Medina et al ., 1986; van der Merwe and Medina, 1989). These factors cause the understory plants of a closed canopy forest to bear 13C values as low as -37, a phenomenon known as the Canopy Effect (Med ina and Minchin, 19 80; Medina et al., 1986; van der Merwe and Me dina, 1989). The average 13C value for these plants is 30.9 (Ehleringer, Field, Lin, and Kuo, 1986). Modern C3 plants that grow in open areas and do not suffer fr om water stress exhibit a 13C range from -26 to -27 (Cerling et al., 1997a). The range of bulk 13C values for all the sampled WCF is -11.39 to -8.3, which, considering analytical and fractionation error, indicates a diet that ranges in isotopic composition from -25.49 0.59 to -22.40 0.59. An adjustment for the Monterey Excursion of -1 changes th e range to approximate ly -26.49 0.59 to -23.40 0.59. With this adjustment, all of the bulk samples have 13C values above the maximum limit (-27) for the Canopy Effect, although the error range of the

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72 Teleoceras sample extends down to -27.08. Even the two brachdyont taxa, Anchitherium clarencei and Aphelops have dietary bulk 13C ranges that preclude them from eating ground-level browse in a closed canopy forest. The serial sampling also does not support a closed-canopy dietary com ponent. All the serial samples for M primus Aphelops and A isonesus indicate diets that have 13C values above -27, except one A isonesus sample that yields a dietary value of -27.06. The error rang e of this sample, along with the higher serial 13C values for this specimen, suggests that this specimen was still not eating in a closed-canopy forest. The range of bulk and serial 13C values for the WCF reveals that the mammals lived and ate in an open habitat, such as a woodland savanna or grassland. Paleoecological interpretations can also be made from the bulk 13C values of the WCF. When C3 plants are suffering water stress, they become enriched in 13C (Ehleringer et al., 1986; Ehleringer and Cooper, 1988; Ehleringer, 1991). During episodes of water stress, plants close their stomata to c onserve water, consequently reducing CO2 intake and enriching the 13C of C3 plant tissues as high as -22 (Ehleringer et al., 1986; Ehleringer and Cooper, 1988; Ehleringer, 1991). As mentioned above, the calibrated isotopic range of the WCF diet is -2 5.49 0.59 to -22.40 0.59. An adjustment for the Monterey Excursion of -1 cha nges the range to approximately -26.49 0.59 to -23.40 0.59. This range suggests that the WCF were feeding off of C3 plants in open areas that peri odically experienced water st ress. This interpretation is supported by the serial sampling, which re veals dietary ranges of -24.36 0.59 to -25.64 0.59 for two serially sampled M primus specimens and -25.02 0.59 to -27.06 0.59 for the two serially sampled A isonesus specimens. The serially

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73 sampled specimens of Aphelops also support an interpreted diet of water-stressed C3 plants, with significantly variant dietary ranges of -23.47 0.59 to -26.82 0.59. The stable carbon isotopic evidence s uggests that the WCF were consuming water-stressed plants in open arid and seasona l environment, such as open-country plains. Interpretations about local seasonal ity can be made from the serial 18O values from the structural carbonate in the enamel of the WCF. Assuming th at equids from the middle Miocene were obligate drinkers like modern equids, the serial sampling should reveal a noticeable curve in 18O values. For M primus, specimens UF221419 and UF221427 display trends that are nearly mi rror images of one another. Enamel mineralization, which begins at the crown, began during the winter for UF 221419, which is evident from the low 18O values at 15 and 10 mm fr om the base of the tooth. Enamel mineralization, which takes about 1.5 to 2.8 years for cheek teeth in modern equids (Bryant et al., 1996a), ended in the summer. Contrastingly, enamel mineralization for UF221427 began in spring or early summer and was mostly completed by winter, according to the high 18O values from 20 to 5 mm from th e tooth base th at are within error of one another. Although modern equid cheek teet h take a minimum of about 1.5 years to mineralize, it is possible for the teeth of Merychippus primus to take less than a year since the teeth are less high-crowned than modern equids. It s hould be noted that each sample along the tooth bears a 18O value that is time-averaged over a few months. The other equid that was serially sampled, A isonesus reveals two distinct curves that are also mirror images. UF221407 appears to have begun enamel mineralization towards the end of summer or fall and continued th rough the entire winter and into the next

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74 summer. UF217590 began enamel mineralizatio n in early summer or spring, in the winter. Modern rhinocerotids are ob ligate drinkers (Clauss et al., 2005). Assuming that Aphelops is also an obligate drinker, the 18O values of the enamel carbonate should reflect any seasonal variation. UF 104227 disp lays considerable variation. Tooth formation began during the 18O lows of winter. There are two summer peaks and three winter troughs, i ndicating that the Aphelops cheek tooth formed over roughly two years. The 18O variation of UF 116827 is not as prono unced as UF 104227, but a curve outside the error ranges is discernible. Tooth mi neralization for UF 104227 began in a summer peak. The curve features two summer peaks and two winter lows, suggesting that the Aphelops molar took slightly more than a year to mineralize. The lower 18O values of UF 116827 indicates that the tooth mineralized during a period of c ooler temperatures than UF 104227. Overall, the 18O variation in both Aphelops specimens supports the interpretation seasonality in northern Florida during the middle Miocene. The variation of 18O values for the serially sampled specimens of M primus A isonesus and Aphelops suggests that the WCF experienced significant seasonality. This stable oxygen isotopic data supports the inte rpretations of periodi c water-stress made from the stable carbon isotopic data. The s easonality experienced by the WCF is typical of the warming that took place in the middle Miocene. The middle Miocene (early Barstovian) WCF represent an interesting transition in the paleodiets of Floridian mammals. The mesodont equid Parahippus leonensis can be found at the early Miocene (Hemingfordian) Thomas Farm locality, from about 19 to 18 Ma (Hulbert and MacFadden, 1991). The rate of wear for P leonensis cheek teeth is

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75 about half of wear rate of grazing equids, indicating a mixe d diet of grass and browse (Hulbert, 1984). This interpretation has been supported by mesowear analyses (Hoffman, unpublished). This suggests that grasses, either C3 or C4, existed in central Florida as far back as 19 Ma, but the mesodont equids at were still consuming significant amounts of browse. Only hypsodont equids, like Acritohippus isonesus were capable of exploiting the more abrasive grasses. Thomas Farm also yields the brachydont equids Anchitherium and Archaeohippus A diminuitive presence of grasses would explain the lack of hypsodont taxa at the Thomas Fa rm site. It was only after C3 grasses became more abundant, by 15.8 Ma in northern Florida, th at equids radiated into hypsodont lineages. Mesowear analyses revealed grazing diets for all five of the hypsodont equids from the last 10 million years. Coupled with previous isotopic data (Table 6-1), it is possible to trace the existence of C3 grasses over the last 10 million years in Florida. All three horses from the Love Site ( Neohipparion trampasense Cormohipparion plicatile and Cormohipparion ingenuum ) have 13C values indicative of a C3-dominated diet. Furthermore, the most positive 13C value of these samples is -10.8, well below -8.7. This indicates that the diets of these horses consisted purely of C3 plants. Since the mesowear analyses indicate that these taxa were primarily gr azers, they must have been feeding on C3 grasses. The 13C values from enamel indicate a range of -26.7 to -24.9 for the consumed plants. This suggests that the equids were eating water-stressed C3 grasses in seasonal, open habitat. This in terpretation compares favorably with other studies. The population dynamics of N trampasense from the Love Site reveal a high rate of tooth wear, comparable to the modern zebra Equus burchelli which indicates a highly abrasive grass-dominated diet (Hulbert, 1982). The presence of discrete age classes at the

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76 site suggests that the area was a wooded grassland savanna with seasonal rains that controlled the migratory and bi rthing patterns (Hulbert, 1982). N trampasense migrated away from the Love site during the wet season to give birth, then re turned during the dry season (Hulbert, 1982). This interpre tation is supported by the range of 13C values, which suggest that the equids at the Love Site were consuming water-stressed grasses. The next site, the Upper Bone Valley Formation, features specimens of Nannippus aztecus that represent the 4.5 Ma level. The three 13C values for N aztecus indicate a diet composed of both C3 and C4 plant material (Table 6-1). Combined with the mesowear grazer classification, N aztecus can be interpreted as an opportunistic grazer, feeding on both C3 and C4 grasses and possibly some browse This level is dated after the global shift in carbon biomass, when C4 grasses became dominant. However, the N aztecus specimens consist of an M1, an M2, a nd an M1/2. First molars are completely mineralized during the weaning process, s uggesting that the isotopic compositions of M1s are influenced by the mothers milk (B ryant et al., 1996a; Fricke and ONeil, 1996; Hoppe et al., 2004). Second molars are not completely mineralized until after the weaning process ends, but they can still re flect the isotopic co mposition of the nursing diet (Bryant et al., 1996a; Fricke and ONeil, 1996; Hoppe et al., 2004). The M2 and M1/2 13C values, therefore, might be skewed. A study conducted on 6 sympatric horses from Upper Bone Valley Formation concluded that, as recently as 5 million years ago, C4 tropical grasses in Florida coexisted with C3 grasses. Using microwear this study showed that Nannippus aztecus along with the sympatric late Hemphillian horse Pseudhipparion simpsoni consumed both C3 and C4 grasses (MacFadden et al., 1999). This st udy substantiates the interpretation of

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77 Nannippus aztecus as a C3/C4 grazer. Furthermore, older N aztecus specimens from the 7 Ma Moss Acres Racetrack site (Table 6-1) have 13C values of -7.9 and -5.3. These values indicate a mixed diet of C3 and C4 plants. Mesowear analyses could not be conducted on this population because the popul ation size was too small (<20). However, if this population behaved similarl y to the younger Upper Bone Valley Nannippus populations (i.e., they were primarily grazing), then this population was likely composed of C3/C4 grazers. Finally, the Leisey Shell Pit represents the 1.5 Ma level. The specimens of Equus leidyi have 13C values that are more nega tive than -1.3, indicating a C4-dominated diet with a minor C3 component. Modern Equus is predominantly a grazer, but is known to eat other locally availa ble plants (Berger, 1986). The isotopic and mesowear data suggests that, like modern Equus Equus leidyi was a dominant C4 grazer at 1.5 Ma. Previous work (MacFadden et al., 1999) as well as the mesowear analyses of various Florida equid populations have shown that C3 grasses were present in Florida from ~10 to ~5 Ma. In light of the microwea r and isotopic data retr ieved from the WCF, it appears that the record of C3 grasses in northern Florida and southern Georgia extends back to at least 15 million years ago. As evidenced by the consumption C3 grasses by a hypsodont taxon, it is possible that C3 grasses forced the adaptation of hypsodonty in ungulates.

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78 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 -12-11-10-9-8-7-6-5-4-3-2-10113C (V-PDB)Microwear Indices (Scratches/Pits) Acritohippus isonesus Neohipparion trampasense Grazers Browsers Pure C3Mixed Diet Pure C4 Figure 6-1. Plot of mi crowear index versus 13C values. The dashed line represents a microwear index of 1.5, the boundary between a browser and a grazer classification. Solid lines mark the boundaries between Pure C3 diet, Mixed diet, Pure C4 diet and transitional zones. 13C values below -8.7 indicate a pure C3 diet. Note that both Acritohippus isonesus and Neohipparion trampasense have microwear indices above 1.5 and 13C values below -8.7, suggesting diets composed purely of C3 grasses.

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79 Table 6-1. Isotopic data for e quids from 4 central Florida sites. Abbreviations: UF ID = catalogue number in Florida Museum of Natural History collections. (Modified woth permission from MacFadden and Cerling, 1996) Taxon Site UF ID Material 13C () 9.5 Ma Level, late Clarendonian, late Miocene Neohipparion trampasense Love Bone Bed 32230 R. P3-M3 -11.6 Cormohipparion plicatile Love Bone Bed 32265 R. P2 -12.6 Cormohipparion plicatile Love Bone Bed 32265 R. P3 -12.5 Cormohipparion plicatile Love Bone Bed 32265 R. P4 -11.0 Cormohipparion plicatile Love Bone Bed 32265 R. M1 -12.0 Cormohipparion ingenuum Love Bone Bed 60396 R. P2 -10.8 Cormohipparion ingenuum Love Bone Bed 35979 R. P2 -10.8 7.0 Ma level, "middle" Hemphillian, late Miocene Nannippus aztecus Moss Acres 69933 R. M3 -7.9 cf. Nannippus Moss Acres None R. P2 -5.3 4.5 Ma level, latest Hemphillian, early Pliocene Nannippus Upper Bone Valley None L. M -6.0 Nannippus aztecus Upper Bone Valley 63633 L. M2 -9.1 Nannippus aztecus Upper Bone Valley 65796 R. M1 -2.4 1.5 Ma level, early Irving tonian, early Pleistocene Equus "leidyi" Leisey 1A 80047 R. M3 -1.5 Equus "leidyi" Leisey 1A None R. P2 -3.5

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80 CHAPTER 7 CONCLUSIONS Stable carbon isotope analyses of th e Willacoochee Creek Fauna, the oldest isotopically sampled taxa in Florida, pr ovide no evidence for the presence of C4 grasses in the diets of ungulates in northern Florid a and southern Georgia at from 15.3 to 15.9 Ma. This suggests that C4 grasses were not present in the area at important time in mammal evolution and, since they are not a si gnificant dietary component, it is unlikely that they were responsible for hypsodonty adaptations. Furthe rmore, the microwear of the most hypsodont taxon from the WCF, Acritohippus isonesus, indicates a grazing diet. Combined with the C3-consuming classification, based on 13C values from bioapatite, the microwear suggests that Acritohippus isonesus ate C3 grasses. This substantiates the presence of C3 grasses in the middle Miocene of northern Florida and supports Fox and Kochs (2003) claim that C3 grasses were responsible for the hypsodonty adaptations. Stable carbon and oxygen isotope values also indicate that the Willacoochee Creek Fauna ate many water-stressed plants and lived in an open, arid, and seasonal environment, such as open-country plains Mesowear analyses and previously publis hed isotope data reveal that the C3 grasses were the primary dietary component in some Floridian horses at ~9.5 Ma. Even after the global carbon biomass shift at ~7 Ma, C3 grasses persisted in Florida and were significant dietary component s until at least ~4.5 Ma. By ~1.5 Ma, it appears that abundance of C3 grasses finally subsided in Florida, where the dominant grazer ( Equus leidyi ) was consuming mostly C4 grass. This long reliance off of C3 grasses suggests

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81 that C3 grasses were a driving mechanism for the appearance of hypsodonty in ungulates. The combinations of mesowear and stable isotope analyses and microwear and stable isotope analyses have proven to be valuable tools in assessing th e origins of hypsodonty. Future work will involve applying these combin ed methods to the northern Great Plains, where there is a rich record of ungulate fossils.

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82 APPENDIX A MESOWEAR VALUES LISTED BY SAMPLE Table A-1. Abbreviations: UF ID = catalogue number in Florida Museum of Natural History collections, CS = Cusp Shape, OR = Occlusal Relief, BVF = Bone Valley Formation, Leisey = Leisey Shell Pit, B = Blunt, R = Round, S = Sharp, H = High, L = Low. UF ID Taxon Locality Material CS OR 62251 Neohipparion trampasense Love Site L. M1 R L 25637 Neohipparion trampasense Love Site L. M1 R L 27992 Neohipparion trampasense Love Site L. M2 R L 32273 Neohipparion trampasense Love Site L. M2 B L 32258 Neohipparion trampasense Love Site R. M2 R L 27991 Neohipparion trampasense Love Site L. M2 R H 32253 Neohipparion trampasense Love Site L. M2 R L 53428 Neohipparion trampasense Love Site L. M2 B L 53427 Neohipparion trampasense Love Site L. M1 B L 32256 Neohipparion trampasense Love Site L. M2 R H 32272 Neohipparion trampasense Love Site L. M2 R H 32252 Neohipparion trampasense Love Site L. M2 R L 53429 Neohipparion trampasense Love Site L. M1/2 B L 53230 Neohipparion trampasense Love Site L. M1/2 R L 53243 Neohipparion trampasense Love Site L. M1/2 R L 53256 Neohipparion trampasense Love Site L. M1/2 R L 53269 Neohipparion trampasense Love Site R. M1/2 B L 53244 Neohipparion trampasense Love Site L. M1/2 B L 53257 Neohipparion trampasense Love Site L. M1/2 B L 53232 Neohipparion trampasense Love Site L. M1/2 R H 53271 Neohipparion trampasense Love Site R. M1/2 B L 53246 Neohipparion trampasense Love Site R. M1/2 R H 53272 Neohipparion trampasense Love Site R. M1/2 B L 53234 Neohipparion trampasense Love Site L. M1/2 B L 53247 Neohipparion trampasense Love Site L. M1/2 B L 53273 Neohipparion trampasense Love Site R. M1/2 R H 53235 Neohipparion trampasense Love Site L. M1/2 B L 53248 Neohipparion trampasense Love Site L. M1/2 B L 53236 Neohipparion trampasense Love Site L. M1/2 R H 53249 Neohipparion trampasense Love Site L. M1/2 R H 53275 Neohipparion trampasense Love Site R. M1/2 B L 53237 Neohipparion trampasense Love Site L. M1/2 B L 53250 Neohipparion trampasense Love Site L. M1/2 R H 53276 Neohipparion trampasense Love Site R. M1/2 S H 53225 Neohipparion trampasense Love Site L. M1/2 B L 53251 Neohipparion trampasense Love Site L. M1/2 R L

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83 Table A-1. Continued UF ID Taxon Locality Material CS OR 53277 Neohipparion trampasense Love Site R. M1/2 R H 53265 Neohipparion trampasense Love Site R. M1/2 B L 53278 Neohipparion trampasense Love Site R. M1/2 R H 53282 Neohipparion trampasense Love Site R. M1/2 R L 96934 Cormohipparion plicatile Love Site R. M2 B L 53338 Cormohipparion plicatile Love Site R. M2 R H 36289 Cormohipparion plicatile Love Site R. M2 B L 27993 Cormohipparion plicatile Love Site R. M2 S H 96933 Cormohipparion plicatile Love Site L. M2 R L 32270 Cormohipparion plicatile Love Site R. M1 B L 32260 Cormohipparion plicatile Love Site L. M2 R L 32250 Cormohipparion plicatile Love Site R. M2 R L 35891 Cormohipparion plicatile Love Site L. M1 R L 32262 Cormohipparion plicatile Love Site L. M2 R L 27316 Cormohipparion plicatile Love Site R. M2 R H 32264 Cormohipparion plicatile Love Site R. M2 R H 32283 Cormohipparion plicatile Love Site L. M2 B L 32266 Cormohipparion plicatile Love Site L. M2 B L 69811 Cormohipparion plicatile Love Site R. M1 R L 53346 Cormohipparion plicatile Love Site R. M1/2 R L 53377 Cormohipparion plicatile Love Site L. M1/2 R H 53347 Cormohipparion plicatile Love Site R. M1/2 R H 53348 Cormohipparion plicatile Love Site R. M1/2 B L 53363 Cormohipparion plicatile Love Site L. M1/2 R L 53379 Cormohipparion plicatile Love Site L. M1/2 B L 53331 Cormohipparion plicatile Love Site R. M1/2 R H 53349 Cormohipparion plicatile Love Site R. M1/2 B L 53364 Cormohipparion plicatile Love Site L. M1/2 R H 53351 Cormohipparion plicatile Love Site R. M1/2 R H 53365 Cormohipparion plicatile Love Site L. M1/2 S L 53352 Cormohipparion plicatile Love Site R. M1/2 R L 53366 Cormohipparion plicatile Love Site L. M1/2 B L 53336 Cormohipparion plicatile Love Site R. M1/2 R H 53353 Cormohipparion plicatile Love Site R. M1/2 S H 53367 Cormohipparion plicatile Love Site L. M1/2 R L 53370 Cormohipparion plicatile Love Site L. M1/2 R L 53339 Cormohipparion plicatile Love Site R. M1/2 R H 53371 Cormohipparion plicatile Love Site L. M1/2 S H 32300 Cormohipparion ingenuum Love Site L. M2 R H 32254 Cormohipparion ingenuum Love Site R. M2 R L 32296 Cormohipparion ingenuum Love Site L. M2 R L 53426 Cormohipparion ingenuum Love Site R. M1 R L 53396 Cormohipparion ingenuum Love Site R. M2 R L 53375 Cormohipparion ingenuum Love Site L. M1/2 R H 53391 Cormohipparion ingenuum Love Site R. M1/2 B L 53395 Cormohipparion ingenuum Love Site R. M1/2 B L 53394 Cormohipparion ingenuum Love Site R. M1/2 R H

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84 Table A-1. Continued UF ID Taxon Locality Material CS OR 53390 Cormohipparion ingenuum Love Site R. M1/2 R H 53389 Cormohipparion ingenuum Love Site R. M1/2 R H 53383 Cormohipparion ingenuum Love Site L. M1/2 R H 53384 Cormohipparion ingenuum Love Site L. M1/2 R H 53385 Cormohipparion ingenuum Love Site L. M1/2 B L 62409 Cormohipparion ingenuum Love Site L. M1/2 R L 96377 Cormohipparion ingenuum Love Site L. M1/2 R H 62417 Cormohipparion ingenuum Love Site R. M1/2 R H 62391 Cormohipparion ingenuum Love Site L. M1/2 R H 62430 Cormohipparion ingenuum Love Site R. M1/2 R H 62398 Cormohipparion ingenuum Love Site L. M1/2 R L 62429 Cormohipparion ingenuum Love Site R. M1/2 R H 62395 Cormohipparion ingenuum Love Site L. M1/2 B L 62427 Cormohipparion ingenuum Love Site R. M1/2 R L 6700 Nannippus aztecus BVF R. M2 R H 57576 Nannippus aztecus BVF L. M1 R 57576 Nannippus aztecus BVF L. M2 R H 212370 Nannippus aztecus BVF R. M1 R H 211769 Nannippus aztecus BVF R. M1/2 R H 208402 Nannippus aztecus BVF R. M1/2 R L 207957 Nannippus aztecus BVF R. M1 R H 203506 Nannippus aztecus BVF R. M1/2 R H 156921 Nannippus aztecus BVF R. M2 R H 156920 Nannippus aztecus BVF R. M1 R H 130079 Nannippus aztecus BVF R. M1/2 R H 124209 Nannippus aztecus BVF R. M1/2 R L 102613 Nannippus aztecus BVF R. M1/2 R H 102612 Nannippus aztecus BVF R. M1/2 R L 102611 Nannippus aztecus BVF R. M1/2 R L 100239 Nannippus aztecus BVF R. M1/2 B L 100241 Nannippus aztecus BVF R. M1/2 B L 93223 Nannippus aztecus BVF R. M1/2 R H 67981 Nannippus aztecus BVF R. M1/2 B L 63630 Nannippus aztecus BVF R. M1/2 R H 55933 Nannippus aztecus BVF R. M1/2 B L 55893 Nannippus aztecus BVF R. M1/2 R L 53953 Nannippus aztecus BVF R. M1 B L 47371 Nannippus aztecus BVF R. M1/2 R L 17252 Nannippus aztecus BVF R. M1 R H 208360 Nannippus aztecus BVF L. M1 R H 211787 Nannippus aztecus BVF L. M1 R H 211892 Nannippus aztecus BVF L. M1 R L 58296 Nannippus aztecus BVF L. M1 R H 63627 Nannippus aztecus BVF L. M1 R L 63633 Nannippus aztecus BVF L. M2 R H 63693 Nannippus aztecus BVF L. M1 R H 63964 Nannippus aztecus BVF L. M1 B L

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85 Table A-1. Continued UF ID Taxon Locality Material CS OR 63967 Nannippus aztecus BVF L. M1 R L 17279 Nannippus aztecus BVF L. M1 R H 47362 Nannippus aztecus BVF L. M2 R L 80090 Equus leidyi Leisey L. M1 B L 85523 Equus leidyi Leisey L. M2 B L 85780 Equus leidyi Leisey R. M1 B L 83800 Equus leidyi Leisey R. M2 B L 85776 Equus leidyi Leisey L. M1 B L 85772 Equus leidyi Leisey R. M1 R L 85771 Equus leidyi Leisey L. M1 B L 82642 Equus leidyi Leisey L. M1 B L 84173 Equus leidyi Leisey L. M1/2 S L 85708 Equus leidyi Leisey L. M1/2 S L 85720 Equus leidyi Leisey L. M1/2 B L 85710 Equus leidyi Leisey L. M1/2 B L 85683 Equus leidyi Leisey L. M1/2 B L 84172 Equus leidyi Leisey L. M1/2 B L 85679 Equus leidyi Leisey L. M1/2 B L 81636 Equus leidyi Leisey L. M1/2 R L 85680 Equus leidyi Leisey L. M1/2 R L 81797 Equus leidyi Leisey L. M1/2 B L 85719 Equus leidyi Leisey L. M1/2 R L 85727 Equus leidyi Leisey L. M1/2 B L 85698 Equus leidyi Leisey L. M1/2 B L 85730 Equus leidyi Leisey L. M1/2 B L 85729 Equus leidyi Leisey L. M1/2 R L 82079 Equus leidyi Leisey L. M1/2 R L 85724 Equus leidyi Leisey L. M1/2 B L 85689 Equus leidyi Leisey L. M1/2 B L 85692 Equus leidyi Leisey L. M1/2 B L

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86 APPENDIX B SERIAL STABLE ISOTOPE VALUES Table B-1. Abbreviations: ELC = Englehar d La Camelia Mine, MGF = Milwhite Gunn Farm Mine, and LC2 = La Camelia 2 Mine. UF ID Taxon Sample Height 13C () 18O () Tooth Site 116827 Aphelops sp. 0 mm -8.37 -1.89 R. MX ELC 116827 Aphelops sp. 5 mm -9.98 -1.95 R. MX ELC 116827 Aphelops sp. 10 mm -9.41 -1.65 R. MX ELC 116827 Aphelops sp. 15 mm -9.91 -1.26 R. MX ELC 116827 Aphelops sp. 20 mm -10.72 -1.42 R. MX ELC 116827 Aphelops sp. 25 mm -10.94 -1.55 R. MX ELC 116827 Aphelops sp. 30 mm -11.44 -1.99 R. MX ELC 116827 Aphelops sp. 35 mm -11.35 -1.19 R. MX ELC 116827 Aphelops sp. 40 mm -11.55 -0.80 R. MX ELC 116827 Aphelops sp. 45 mm -11.28 -0.90 R. MX ELC 116827 Aphelops sp. 50 mm -11.72 -0.31 R. MX ELC 104227 Aphelops sp. 0 mm -9.76 0.71 Unident. MGF 104227 Aphelops sp. 5 mm -10.55 2.34 Unident. MGF 104227 Aphelops sp. 10 mm -10.40 1.87 Unident. MGF 104227 Aphelops sp. 15 mm -10.53 1.22 Unident. MGF 104227 Aphelops sp. 20 mm -10.54 3.46 Unident. MGF 104227 Aphelops sp. 25 mm -10.29 3.15 Unident. MGF 104227 Aphelops sp. 30 mm -10.39 1.67 Unident. MGF 104227 Aphelops sp. 35 mm -10.73 1.60 Unident. MGF 221419 Merychippus primus 0 mm -9.26 1.99 L. P4 ELC 221419 Merychippus primus 5 mm -10.54 0.67 L. P4 ELC 221419 Merychippus primus 10 mm -10.19 0.15 L. P4 ELC 221419 Merychippus primus 15 mm -9.27 0.15 L. P4 ELC 221415 Merychippus primus 0 mm -9.39 1.15 R. P3 ELC 221415 Merychippus primus 5 mm -9.66 2.90 R. P3 ELC

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87 Table B-1. Continued UF ID Taxon Sample Height 13C () 18O () Tooth Site 221415 Merychippus primus 10 mm -9.72 2.65 R. P3 ELC 221415 Merychippus primus 15 mm -9.49 2.48 R. P3 ELC 221415 Merychippus primus 20 mm -9.50 2.83 R. P3 ELC 221407 Acritohippus isonesus 0 mm -9.94 1.12 R. P3/4 ELC 221407 Acritohippus isonesus 5 mm -10.16 0.25 R. P3/4 ELC 221407 Acritohippus isonesus 10 mm -10.34 0.36 R. P3/4 ELC 221407 Acritohippus isonesus 15 mm -9.92 0.97 R. P3/4 ELC 221407 Acritohippus isonesus 20 mm -10.63 1.68 R. P3/4 ELC 221407 Acritohippus isonesus 25 mm -10.66 2.56 R. P3/4 ELC 217590 Acritohippus isonesus 0 mm -10.52 0.62 L. P4 LC2 217590 Acritohippus isonesus 5 mm -10.33 2.01 L. P4 LC2 217590 Acritohippus isonesus 10 mm -10.70 2.37 L. P4 LC2 217590 Acritohippus isonesus 15 mm -10.94 2.13 L. P4 LC2 217590 Acritohippus isonesus 20 mm -11.78 2.16 L. P4 LC2 217590 Acritohippus isonesus 25 mm -11.96 1.82 L. P4 LC2

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102 BIOGRAPHICAL SKETCH Jonathan Hoffman was born on June 11, 1981 in Phoenix, Arizona. The oldest of three children, he grew up in Phoenix and graduated from North High School in 1999. He received his B.A. in geology from Occident al College in 2003. Jonathan received his M.S. in the geological sciences from the Un iversity of Florida in 2006. He plans to pursue a doctorate degree and continue research in verteb rate paleontology.