PHYLOGENETIC SYSTEMATICS, BIOCHRONOLOGY, AND PALEOBIOLOGY
OF LATE NEOGENE HORSES (FAMILY EQUIDAE) OF THE GULF
COASTAL PLAIN AND THE GREAT PLAINS
RICHARD CHARLES HULBERT, JR.
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
The members of my supervisory committee, Drs. Bruce J. MacFadden,
S. David Webb, and Douglas S. Jones, aided the completion and
improved the content of this study in many ways. Dr. MacFadden
suggested the initial proposal, a study of the Love Site Equidae, but
has masterfully guided the project through its convoluted evolution
to its present form. He has continually gone the extra step to
provide me with support and equipment. Dr. Webb has shared with me
his considerable expertise of ungulate evolution and Florida's
prehistory. Not the least was a suggestion to take a close look at
the holotype of "Merychippus" westoni. The manuscript has greatly
benefited from their combined editorial skill. I also thank Drs.
Ronald Wolff and Jon Reiskind, who also participated in the
qualifying and final exams, and provided insightful criticism.
Without the fossil specimens, this study would not exist. The
following individuals and institutions allowed me access and
permission to study specimens in their collections during the course
of this study: R. H. Tedford, American Museum of Natural History; M.
R. Voorhies, University of Nebraska State Museum; E. L. Lundelius,
Texas Memorial Museum; G. E. Schultz, West Texas State Universtiy; J.
H. Hutchison, Universtiy of California, Berkeley; D. P. Whistler, Los
Angeles County Museum; C. Smart, Academy of Natural Sciences of
Philadelphia; T. M. Bown, United States Geological Survey, Denver; W.
W. Dalquest, Midwestern State University; L. D. Martin, University of
Kansas; and J. S. Waldrop. Ron and Pat Love and John Shimfessel
graciously notified the Florida State Museum of fossils discovered on
their respective properties, and allowed museum field crews to
collect additional specimens. The following individuals donated
fossil specimens to the Florida State Museum that were used in this
study: Donald Crissinger, John Waldrop, Danny Bryant, Frank Garcia,
Larry Martin, George Heslep, Jerry Case, Howard Converse, Gale
Zelnick, James Ranson, Joe Larned, Craig Patrick, Mark Patrick,
Earlene Mitchell, Jeff Walker, Roy Burgess, Clifford Jeremiah, Eric
Kendrew, Larry Lawson, Jon Bryan and Rick Carter. The latter
individual in particular has made numerous unselfish contributions of
Bone Valley specimens in the last few years. Collectively, this
group of individuals has increased our knowledge of Bone Valley
The excellent specimen illustrations are by Wendy Zomlefer and
Gerald Masters. Dr. R. Tedford has allowed me use of unpublished
illustrations prepared by Frick personal in the 1960s. Russell
McCarty and Howard Converse prepared many of the specimens, and
sectioned numerous teeth. During the early phases of the study,
curation of the Love Site equids was aided by Diderot Gicca and Troy
Dr. M. 0. Woodburne provided a copy of J. P. Quinn's Master's
thesis. Dr. Charles Smart took the time to locate the lectotype and
paratype of Protohippus supremus at a rather hectic moment during the
SVP meetings. I also benefited from discussions with Jack Wilson on
Gulf Coast biostratigraphy.
My tenure as a graduate student at Florida has been blessed with
close camaraderie with my fellow students and the museum VP staff,
and this study bears witness to their helpful support and input.
Specifically, I thank Gary Morgan, Ann Pratt, Jon Becker, Steve
Emslie, Mary Ellen Ahearn, David Wright, Roger Portell and Art Poyer
for their many and diverse contributions.
Finally, I thank my family for their support, and for offering
temporary refuge from the world of academia and fossil horse teeth.
My visits to various museums across the country, a crucial aspect of
this study, were financed by a bequest from my grandmother, Mary
Peterson. This study is what results from taking an impressionable
young child to see the dinosaurs at the Field Museum. Once again, my
companions from Richard Adams to Roger Zelazny, inclusive always
provided a necessary escape from reality when called upon.
TABLE OF CONTENTS
LIST OF TABLES ...................................................
LIST OF FIGURES................................................
KEY TO ABBREVIATIONS...........................................
1 INTRODUCTION ...............................................
2 HISTORY OF PREVIOUS WORK ON GULF COASTAL PLAIN EQUIDS......
3 MATERIALS, METHODS AND TERMINOLOGY.........................
Materials ...................................... ...........
Ontogenetic and Individual Variation in Equid
4 DESCRIPTION OF GULF COASTAL PLAIN EQUID LOCALITIES.........
Northern Peninsular Florida ..............................
Southern Peninsular Florida..............................
Texas Gulf Coastal Plain .................................
5 SYSTEMATIC PALEONTOLOGY....................................
Order Perissodactyla Owen, 1848
Family Equidae Grey, 1821
Subfamily Equinae Steinmann and Dbderlein, 1890..........
Tribe Hipparionini Quinn, 1955 ..........................
Genus Neohipparion Gidley, 1903....................... 46
Neohipparion affine (Leidy), 1869 ................... 48
Neohipparion trampasense (Edwards), 1982............ 57
Neohipparlon eurystyle (Cope), 1893................. 77
Genus Pseudhipparion Ameghino, 1904 ................... 90
Pseudhipparion sp . ..... . ......................... 91
Pseuanipparion curtivallum (Quinn), 1955.............. 92
Pseudhipparion skinneri Webb and Hulbert, 1986...... 93
Pseudhipparion simpsoni Webb and Hulbert, 1986...... 94
Genus Nanippus Matthew, 1926 ........................ 96
Nannippus fricki new species........................ 99
Nannippus sp., cf. Nannippus fricki ................. 112
Nannippus westoni (Simpson), S3T new combination... 117
Nannippus minor (Sellards), 1916 .................... 136
Genus CormohippF on Skinner and MacFadden, 1977...... 156
Cormohipparion sphenodus (Cope), 1889............... 159
Cormohipparlon occidentale (Leidy), 1856............ 164
Cormohipparion plicatile (Leidy),
1887 new combination ........................... 174
Cormohipparion ingenuum (Leidy),
1885 new combination ............................ 218
Cormohiiparion emsliei new species.................. 238
Genus Hipparion de Cristol, 1832..................... 262
Hipparion shirleyi MacFadden, 1984.................. 263
Hipparion tehonense (Merriam), 1916................ 265
Hipparion sp., c7. H. tehonense (Merriam), 1916..... 267
Tribe Equini Quinn, 195 ............................... 276
Subtribe Protohippina Quinn, 1955 new rank............. 277
Genus Calippus Matthew and Stirton, 1930.............. 277
Subgenus Calippus Matthew and Stirton, 1930.......... 282
Cal. (Ca ippus)proplacidus (Osborn),
1918 new combination ........................... 283
Cal. (Calippus) placidus (Leidy), 1869 .............. 298
C T. (Lalippus) regulus Johnston, 1937.............. 304
CT . (Calippus) sp. ............................... . 319
CaT. (Calippus) elachistus new species.............. 320
SuEgenus Grammohippus new subgenus ................... 331
?Cal. (Grammohippus) circulus (Quinn),
1955 new combination .... ........................ 334
Cal. (Grammohippus) martini Hesse, 1936............. 341
CaT. (Grammohippus) cerasinus new species........... 360
T a. (Grammohippus) hondurensis (Olson and
McGrew), 1941 new combination .................... 377
Cal. (Grammohippus) sp., cf. Cal. hondurensis ....... 383
a1T. (Grammohippus) maccartyi new species........... 384
Genus Protohippus Leidy, 8I7 S ........................ 392
Protohippus perditus Leidy, 1858 .................... 394
Protohippus supremus Leidy, 1869 .................... 410
Protohlppus gldleyi new species ..................... 423
Subtribe Equina new subtribe........................... 436
Genus Pliohippus Marsh, 1874 ......................... 438
cf. Pliohippus sp. ......................... ...... 440
Genus Astronippus Stirton, 1940 ...................... 443
Astrohippus stockii (Lance), 1950 ................... 444
Genus Dinohippus - Qinn, 1955......................... 444
Dinohippus sp. .................................... . 446
Dinohippus mexicanus (Lance), 1950.................. 448
6 PHYLOGENETIC ANALYSIS AND CLASSIFICATION................... 449
Introduction and Historical Perspective .................. 449
Methods .................................................. 456
Results and Classification .............................. 469
Comparisons with Previous Phylogenies.................... 515
7 BIOCHRONOLOGY, BIOSTRATIGRAPHY, AND SPECIES DYNAMICS....... 519
Biostratigraphy ........................................ 523
Diversity and Extinction Patterns ........................ 527
8 CONCLUSIONS AND SUMMARY ................................... 532
REFERENCES CITED ............................................... 551
BIOGRAPHICAL SKETCH............................................. 570
LIST OF TABLES
Table 1. Moss Acres Racetrack Site faunal list .................. 32
Table 2. Neohipparion affine upper cheekteeth statistics......... 53
Table 3. Neohipparion affine lower cheekteeth statistics......... 55
Table 4. Neohipparion trampasense upper cheekteeth statistics.... 65
Table 5. Neohipparion trampasense lower cheekteeth statistics.... 71
Table 6. Neohipparion eurystyle upper cheekteeth statistics...... 82
Table 7. Neohipparion eurystyle lower cheekteeth statistics...... 84
Table 8. Measurements of individual Nannippus cheekteeth......... 105
Table 9. Nannippus fricki upper cheekteeth statistics............ 108
Table 10. Nannippus westoni upper cheekteeth statistics........... 121
Table 11. Measurements of medial metapodials of Nannippus......... 129
Table 12. Inventory of Moss Acres skeletons of Nannippus minor.... 140
Table 13. Nannippus minor upper cheekteeth statistics............. 141
Table 14. Nannippus minor lower cheekteeth statistics............. 147
Table 15. Measurements of individual Cormohipparion cheekteeth.... 163
Table 16. Mandibular measurements of hipparionines................ 168
Table 17. Frequency of plications in lower cheekteeth
of Cormohipparion .................................... 169
Table 18. Cormohipparion plicatile upper cheekteeth statistics.... 180
Table 19. Cormohipparion plicatile and Cor. ingenuum lower
cheekteeth statistics .................................. 193
Table 20. Variation in basal tooth length in equid populations.... 198
Table 21. Median values of Cormohipparion fossette plications..... 210
Table 22. Cormohipparion ingenuum upper cheekteeth statistics ..... 223
Table 23. Cormohipparion emsliei upper cheekteeth statistics...... 249
Table 24. Cormohipparion emsliei lower cheekteeth statistics...... 250
Table 25. Measurements of medial metapodials of
Cormohipparion emsliei and other equids................. 257
Table 26. Comparison of unworn crown height of equids............. 258
Table 27. Hipparion upper cheekteeth statistics................ .. 268
Table 28. Measurements of individual cheekteeth of Hipparion ...... 270
Table 29. Calippus proplacidus and Cal. placidus upper
cheekteeth statistics.................................. 286
Table 30. Calippus proplacidus and Cal. placidus lower
cheekteeth statistics................................... 288
Table 31. Measurements of cheekteeth of Calippus proplacidus...... 290
Table 32. Calippus regulus and Calippus elachistus upper
cheekteeth staEistics................................... 310
Table 33. Calippus regulus and Calippus elachistus lower
cheekteet statistics................................... 312
Table 34. Measurements of cheekteeth of Calippus sp. .............. 318
Table 35. Measurements of cheekteeth of Calippus elachistus ....... 327
Table 36. Measurements of cheekteeth of Calippus (Grammohippus)... 338
Table 37. Calippus martini upper cheektooth statistics ............ 348
Table 38. Calippus martini lower cheektooth statistics............ 350
Table 39. Calippus cerasinus upper cheektooth statistics.......... 370
Table 40. Calippus cerasinus lower cheektooth statistics.......... 372
Table 41. Protohippus spp. upper cheektooth statistics............ 399
Table 42. Protohippus spp. lower cheektooth statistics............ 401
Table 43. Measurements of cheekteeth of Protohippus ............... 405
Table 44. Comparison of cranial characters of Protohippus
and Pliohippus .......................................... 407
Table 45. Measurements of cheekteeth of Florida equines........... 442
Table 46. Character matrix for 57 equid species................... 459
Table 47. Description of characters and character states.......... 463
Table 48. Consistency indices for characters in Figure 69 ......... 479
Table 49. Classification of the Hipparionini and Equini ........... 513
Table 50. Equid species diversity analysis ....................... 528
Table 51. Summary of late Neogene equid distributions............. 534
LIST OF FIGURES
Figure 1. Dental nomenclature and measurements ................... 19
Figure 2. Map of Florida with locations of major fossil sites.... 27
Figure 3. Neohipparion affine cheekteeth from Texas.............. 52
Figure 4. Facial region of Neohipparion trampasense.............. 61
Figure 5. Neohipparion trampasense toothrows..................... 62
Figure 6. Neohipparion trampasense upper cheekteeth.............. 64
Figure 7. Neohipparion trampasense lower cheekteeth.............. 70
Figure 8. Neohipparion eurystyle cheekteeth from Florida.......... 81
Figure 9. Type palate of Nannippus fricki ....................... 102
Figure 10. Nannippus fricki upper cheekteeth from Nebraska........ 104
Figure 11. Nannippus sp., cf. Nan. fricki cheekteeth.............. 115
Figure 12. Nannippus westoni upper cheekteeth ..................... 123
Figure 13. Nannippus westoni lower cheekteeth..................... 124
Figure 14. Medial metapodials of Nannippus from Florida........... 128
Figure 15. Late Hemphillian Nannippus minor upper cheekteeth ...... 143
Figure 16. Late Hemphillian Nannippus minor lower cheekteeth...... 144
Figure 17. Outline of partial skull of Nannippus minor............ 151
Figure 18. Nannippus minor cheekteeth from Moss Acres............. 153
Figure 19. Cormohipparion sphenodus cheekteeth.................... 162
Figure 20. Principal components analysis of Cormohipparion
occidentale and Neohipparion affine.................... 171
Figure 21. Cormohipparion plicatile maxilla ...................... 182
Figure 22. Cormohipparion plicatile upper toothrows .............. 183
Figure 23. Cormohipparion plicatile upper cheekteeth .............. 185
Figure 24. Cormohipparion plicatile ramus showing diastema........ 190
Figure 25. Cormohipparion plicatile lower toothrows............... 191
Figure 26. Cormohipparion plicatile lower cheekteeth.............. 192
Figure 27. Histograms of Cormohipparion plicatile and Cor.
ingenuum upper premolars ............................. 201
Figure 28. Histograms of Cormohipparion plicatile and Cor.
ingenuum upper molars ................................. 203
Figure 29. Results of discriminant analysis ...................... 205
Figure 30. Histograms of premolar fossette plications............. 212
Figure 31. Histograms of molar fossette plications................ 214
Figure 32. Histograms of fossette plications of Cormohipparion
occidentale from Nebraska ............................. 215
Figure 33. Cormohipparion ingenuum maxilla ....................... 225
Figure 34. Cormohipparion ingenuum upper toothrows................ 226
Figure 35. Cormohipparion ingenuum lower toothrows ............... 227
Figure 36. Cormohipparion ingenuum lower cheekteeth............... 228
Figure 37. Cormohipparion emsliei holotype and topotypes.......... 243
Figure 38. Cormohipparion emsliei upper cheekteeth................ 246
Figure 39. Cormohipparion emsliei lower cheekteeth................ 248
Figure 40. Cormohipparion emsliei metatarsal III................. 256
Figure 41. APL vs. TRW for Cormohipparion and Nannippus species... 259
Figure 42. Maxilla and cheekteeth of Florida Hipparion ............ 272
Figure 43. Plot of equid toothrow length vs. muzzle width ......... 281
Figure 44. Calippus proplacidus cheekteeth from Texas ............. 291
Figure 45. Calippus sp. and Calippus proplacidus from Florida..... 292
Figure 46. Molar BAPL vs. PRL for four species of Calippus........ 293
Figure 47. Molar APL vs. unworn crown height for Calippus......... 294
Figure 48. Calippus placidus upper cheekteeth from Texas .......... 301
Figure 49. Calippus regulus skull and mandible................... 309
Figure 50. Molar BAPL for four populations of Calippus............ 317
Figure 51. Calippus elachistus cheekteeth from the Love Site...... 324
Figure 52. Calippus elachistus holotype mandible .................. 325
Figure 53. Early Hemphillian Calippus elachistus cheekteeth ....... 326
Figure 54. ?Calippus circulus upper cheekteeth.................... 337
Figure 55. Calippus spp. from Florida............................. 347
Figure 56. Molar BAPL vs. PRL for four species of Grammohippus.... 352
Figure 57. Calippus cerasinus holotype skull and referred jaw..... 365
Figure 58. Calippus cerasinus upper cheekteeth.................... 367
Figure 59. Calippus cerasinus lower cheekteeth.................... 369
Figure 60. Calippus maccartyi cheekteeth from Florida............. 387
Figure 61. Calippus maccartyi holotype mandibular symphysis ....... 388
Figure 62. Protohippus upper cheekteeth from Florida.............. 404
Figure 63. Protohippus supremus upper cheekteeth from Nebraska.... 415
Figure 64. Protohippus gidleyi toothrows from the Love Site....... 428
Figure 65. Protohippus gidleyi cheekteeth from the Love Site ...... 429
Figure 66. Timing of protocone connection and hypoconal groove
closure in upper premolars of Protohippus gidleyi ..... 431
Figure 67. Cladograms of previous phylogenetic hypotheses
regarding the Equinae ................................. 452
Figure 68. Forsten's cladogram of the Hipparionini ................ 454
Figure 69. Computer-generated cladogram of 45 equid taxa .......... 472
Figure 70. Computer-generated cladogram of 45 equid taxa using
only highly consistent characters ..................... 474
Figure 71. Computer-generated cladogram of genotypic species...... 476
Figure 72. Computer-generated cladogram of Barstovian species..... 478
Figure 73. Most parsimonious cladogram of the Hipparionini ........ 484
Figure 74. Preferred cladogram of the Hipparionini ................ 486
Figure 75. Most parsimonious cladogram of the Equini .............. 503
Figure 76. Preferred cladogram of the Equini ...................... 505
Figure 77. Chronologic distribution of equid species.............. 521
Figure 78. Equid diversity patterns in the late Neogene........... 530
KEY TO ABBREVIATIONS
AMNH--Department of Vertebrate Paleontology, American Museum of
Natural History, New York.
ANSP--Academy of Natural Sciences. Philadelphia.
F:AM--Frick American Mammals, now housed with AMNH collection.
JWT--C. S. Johnston collection, housed in PPM.
KUVP--University of Kansas Museum of Paleontology, Lawrence.
LACM--Natural History Museum of Los Angeles County, Los Angeles.
LACM(CIT)--California Institute of Technology collection, now housed
with LACM collection.
MSU--Midwestern State Universtiy, Wichita Falls, Texas.
PPM--Panhandle-Plains Historical Museum, Canyon, Texas.
SDSM--Museum of Geology, South Dakota School of Mines and Technology,
TAMU--Texas A & M University collection, now housed with TMM
TMM--Texas Memorial Museum, University of Texas, Austin.
TRO--Timberlane Research Organization, private collection of John
Waldrop, Lake Wales, Florida.
UCMP--University of California Museum of Paleontology, Berkeley.
UCR--Department of Earth Sciences, University of California,
UF--Florida State Museum, University of Florida, Gainesville.
UF/FGS--Florida Geological Survey collection of fossil vertebrtes,
now housed with UF collection.
UNSM--University of Nebraska State Museum, Lincoln.
USNM--National Museum of Natural History, Smithsonian Institution,
WM--Walker Museum collection, now housed at the Field Museum of
Natural History, Chicago.
WT--West Texas State University collection, housed in PPM.
Morphological Characters and Terms
DPOF--dorsal preorbital fossa (= lacrimal or nasomaxillary fossa).
R, L--right, left.
P/p--upper/lower premolar (e.g. P4 is an upper fourth premolar).
M/m--upper/lower molar (e.g. m2 is a lower second molar).
D/d--upper/lower deciduous tooth (e.g. dp2 is a deciduous lower
P34, p34, DP34, dp34, M12, m12--collective terms for
indistinguishable isolated teeth (e.g. P34 refers to upper third
or fourth premolars).
HI--hypsodonty index (=maximum M12 MSCH/mean M12 BAPL)
Those in uppercase refer to upper dentitions; lowercase to lower
dentitions. Measurements taken on oclusal surfaces of cheekteeth are
illustrated in Figure 1.
APL--maximum anteroposterior length, excluding the ectoloph and
BAPL--anteroposterior length at the base of the crown.
TRW--transverse width from mesostyle to lingual-most part of the
PRL--maximum length of the protocone, excluding spur and connection
PRW--maximum width of the protocone perpendicular to PRL.
MSCH--crown height measured from the occlusal surface to the base of
the crown along the mesostyle.
UTRL--upper toothrow length from the anterior-most projection of the
P2 to the posterior-most part of the M3.
UDL--upper postcanine diastema length, measured between the alveoli
of the C and the P2 (excludes DP1 if present).
ROC--radius of curvature, measured on the mesostyle (Skinner and
apl--maximum anteroposterior length from the paralophid to the
bapl--anteroposterior length at the base of the crown.
atw--transverse width from the protoconid to the metaconid.
ptw--transverse width from the hypoconid to the metastylid.
entl--anteroposterior length of the entoflexid.
mml--length from the anterior-most point of the metaconid to the
posterior-most point of the metastylid.
mcch--crown height measured from the occlusal surface to the base of
the crown along the metaconid.
ltrl--lower toothrow length measured from the anterior-most part of
the p2 to the posterior-most point of the m3.
Idl--lower postcanine diastema length measured between the alveoli of
the c and p2 (excluding dpi if present).
s--sample standard deviation.
V--sample coefficient of variation expressed as a percentage.
r--sample correlation coefficient.
OR--observed range of a sample.
As several genera in this study start with the same letter, the use
of the usual abbreviation for a genus (the first letter) might cause
confusion in some cases. Therefore, the following abbreviations are
uniformly used throughout the study to resolve any possible
ma--megaanna, millions of years before present on the radioisotopic
l.f.--local fauna, used in the sense of Tedford (1970).
n. sp.--new species.
n. subg.--new subgenus.
n. comb.--new combination.
CI--consistency index, used in comparing cladograms.
FSM VP loc.--Florida State Museum Vertebrate Paleontology collection
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
PHYLOGENETIC SYSTEMATICS, BIOCHRONOLOGY, AND PALEOBIOLOGY
OF LATE NEOGENE HORSES (FAMILY EQUIDAE) OF THE GULF
COASTAL PLAIN AND THE GREAT PLAINS
Richard Charles Hulbert, Jr.
Chairman: Bruce J. MacFadden
Major Department: Zoology
Ten genera and thirty-four species of the subfamily Equinae
(Mammalia, Perissodactyla, Equidae) are described from the late
Miocene-early Pliocene (late Barstovian-latest Hemphillian) of the
Gulf Coastal Plain of Florida and Texas, including new species of
Nannippus, Cormohipparion, Protohippus and Calippus. Hippotherium
ingenuum Leidy and H. plicatile Leidy are referred to Cormohipparion,
and Merychippus westoni Simpson to Nannippus. These referrals are
based on voluminous new material from the latest Clarendonian Love
Site (Alachua County, Florida). Nine species of equids are recog-
nized at the Love Site, and are described in detail. This site plays
a major role in understanding North American equid systematics,
phylogeny and paleoecology in the late Miocene. The horses of the
following sites or faunas are also extensively reviewed: Cold
Spring, Lapara Creek, Mixson's Bone Bed, Moss Acres Racetrack,
Withlacoochee River 4A, and the Bone Valley Region. Five distinct
faunal assemblages in stratigraphic superposition are recognized from
the Bone Valley Formation, each with a diagnostic suite of equids.
Comparisons with equid faunas from the Great Plains reveals little
distinctive provinciality between these two regions in the late
Miocene, as they have many species in common. This similarity allows
a biochronologic zonation of the period between 16.5 and 4.5 million
years ago (ma) into nine biochrons based on concurrent range zones of
two or three equid species.
Phylogenetic analysis indicates that the advanced Equinae form a
monophyletic group comprised of two tribes, the Hipparionini and
Equini. The Hipparionini consists of two major clades, one with
Neohipparion and Pseudhipparion, the other with Hipparion, Cormo-
hipparion and Nannippus. Two clades are also recognized in the
Equini, one with Protohippus and Calippus, the other with Pliohippus,
Astrohippus and Equus. Species previously assigned to the paraphy-
letic grade "Merychippus" are classified in their phylogenetically
correct positions. Equid evolution is characterized by frequent
parallelisms and character reversals that complicate phylogenetic
reconstruction. Thus, computer-generated, most parsimonious
cladograms sometimes produce evolutionarily unlikely scenarios.
Hipparionines and protohippines numerically and taxonomically
dominated North American equid faunas until about 6.5 ma; then
equines predominated. Protohippines became extinct about 6.2 ma, and
hipparionines about 2.0 ma.
During the later part of the Miocene, between about 14 and 6 ma,
numerous lineages of equids flourished in apparent sympatry across
North America. By the middle Pliocene (at about 4 ma), only a remnant
was left of this great radiation. Living horses, represented by the
single Old World genus Equus, display little of the morphological (and
presumably ecological) diversity that once characterized the family
Equidae. Therefore, our comprehension of the rise and fall of North
American equid diversity must be based primarily on their fossilized
remains, supplemented with information derived from other components
of the biota, and from various geological disciplines. Fortunately,
the fossil record of the Equidae is relatively complete and abundant,
sometimes overwhelmingly so. This has led to a proportionally large
body of literature concerning fossil equids, yet their systematics and
phylogenetic relationships are not well understood. Most previous
studies have either dealt with equids from a limited geographic
region, often from a single site (e.g. Leidy, 1885; Merriam, 1919;
Richey, 1948; Stirton, 1955; Forsten, 1975; Edwards, 1982), or present
overviews of equid evolution at the generic level (e.g. Gidley, 1907;
Matthew, 1926; Stirton, 1940). While not impuning the importance and
value of such studies, they do not provide the detailed, compre-
hensive, integrated information necessary to fully understand the
late Miocene equid radiation and subsequent decline. Comprehensive
generic reviews of some taxa have recently appeared (MacFadden, 1984a;
Webb and Hulbert, 1986), and for the first time modern phylogenetic
systematic methods have been used with this group of horses. Rigorous
phylogenetic cladisticc) analysis is now recognized as a necessary
prerequisite to meaningful derivative studies can be attempted (Cra-
craft, 1981). Most of the present study (Chapters 5 and 6) documents
the results of this type of systematic analysis. They in turn provide
the foundation for Chapter 7, which presents the results of studies
into various aspects of the late Miocene equid radiation.
This study originated as an analysis of an equid community
recovered from a single locality in north-central Florida, the late
Clarendonian Love Site. A preliminary review by other investigators
indicated that seven types of horses were represented at this one
site, and that most were closely related to well known species (Webb
et al., 1981). Detailed study, based on more specimens, however, did
not confirm these conclusions. Eventually, I have come to recognize
nine species at this site, of which five were undescribed when I
started this project in 1981, and three that belong to previously
poorly known species (see Chapter 5 for details). During the course
of this study it became apparent that an analysis of a single site, no
matter how detailed, was too limited. Instead, lineages had to be
traced through time, to produce a much broader understanding of
changes in diversity and faunal composition. Also, this period (ca.
1981-1986) witnessed much more widespread application of phylogenetic
systematic methods in vertebrate paleontology, and a deeper
appreciation of the information they produce (Wiley, 1981; Cracraft,
1981). With this in mind, it became obvious that a rigorous
phylogenetic analysis of the Equinae was needed before broader
questions could be answered.
The scope of this project was therefore widened to encompass the
equids from the last of the three great Miocene chronofaunas, the
Clarendonian Chronofauna (Webb, 1977). This interval includes the
late Barstovian, Clarendonian, and early Hemphillian Land Mammal Ages,
and lasted from about 14 to 6 million years ago. I have not attempted
to study all North American equids from this extensive period in equal
detail, but have focused on particular groups and geographic regions.
Geographically, the regions analyzed in greatest detail are the Gulf
Coastal Plain and the Great Plains. Earlier in the Miocene, these two
regions differed substantially in some aspects of their vertebrate
communities (Webb, 1977, and references therein), although they had
similar equids in common. Later, by about 15 ma, these differences
ceased, and the two exhibited broad faunal continuity (Webb, 1977;
Tedford et al., in press). It will be documented in Chapter 5 that
for the next ten million years they shared many equid species. As for
taxa, principal attention is given to two groups of advanced equids,
the hipparionines and the protohippines. Together they contributed to
most of the diversity witnessed during the height of the Clarendonian
Chronofauna (Chapter 7). Equines were apparently much rarer in the
Gulf Coastal Plain than these two groups, and did not undergo
significant diversification until the middle Hemphillian. They are
treated in much less detail in Chapter 5 than the others. I have also
chosen to ignore the anchitherine (browsing) equids of this period.
They are also rare in the Gulf Coastal Plain, and are in great need of
taxonomic revision, which would be a large study in itself.
HISTORY OF PREVIOUS WORK ON GULF COASTAL PLAIN EQUIDS
The history of vertebrate paleontology in Florida spans little more
than a century. During this period many important Neogene localities
have been discovered, along with literally thousands of specimens.
From the beginning, equids have played a major role in biochronolog-
ical correlation of Florida's vertebrate-bearing deposits with those
of the West, as well as correlation of localities within the state.
Their abundance at most terrestrial sites, wide distributions and
rapid evolution enable them to be useful biostratigraphic indicators.
Knowledge of Florida's fossil equids is quite dynamic, and shows no
sign of stopping. Indeed, since the initiation of this project in
1981, several new lower horizons in the Bone Valley Region with horse
remains were discovered, and the extremely important Moss Acres
Racetrack Site with its associated skeletons was first worked in 1984.
Joseph Leidy described the first two species of equids to be named
from Florida in 1885 and 1887. They both were based on isolated teeth
from Mixson's Bone Bed (see Chapter 4 for detailed discussions of the
geology, fauna and biochronology of this and other localities
mentioned in this chapter), the first major late Neogene site
discovered in Florida. Although based on rather inadequate material
by modern standards, and described without adequate comparison with
other North American equids, both of Leidy's species (Hippotherium
ingenuum and H. plicatile) are still valid (Chapter 5). Cope (1889)
synonymized H. ingenuum with an older name of Leidy, H. gratum, and
this synonymy was followed by Lucas in his posthumous collaborative
review of the Mixson l.f. with Leidy (Leidy and Lucas, 1896). Gidley
(1907) disagreed, and considered H. ingenuum a valid species, as have
all subsequent authors.
In the first decades of the 20th Century, vertebrate fossils began
to be routinely recovered as a by-product of large-scale phosphate
mining in Florida. This occurred in both the "hard-rock" phosphate
deposits of northern peninsular Florida (e.g. Hay, 1916), and in the
southern, "land-pebble" deposits (Sellards, 1910; 1916). The latter
area, better known as the Bone Valley Region, has ever since been a
valuable source of vertebrate fossils, as its name implies. Sellards
(1915; 1916) reported on the first remains of horses recovered from
the Bone Valley Formation. He recognized three species in these
deposits, the two previously named by Leidy, H. ingenuum and H. pli-
catile, and a new species, the very small H. minor. H. minor is now
known to be the most abundant horse in the Upper Bone Valley Fauna.
Simpson (1930) later reviewed the Bone Valley Fauna, recognized the
same three species as had Sellards (1916), and established a fourth,
H. (Neohipparion) phosphorum. Sellards (1916) and Simpson (1930) both
thought that the faunas from Mixson's, from the northern phosphate
deposits (other Alachua Formation sites), and from the Bone Valley
Formation were all roughly contemporaneous, and that they shared many
species in common (including equids). Simpson (1930) also described
"Merychippus" westoni from Gilchrist County, from what he thought was
the Hawthorn Formation. This geologic assignment was primarily based
on his interpretation of the morphology and stage of evolution repre-
sented by the heavily worn type specimen. Further discoveries suggest
that Simpson was incorrect in his assessment of the specimen's age and
morphology (see Chapter 5).
Following Simpson's (1930) study, little original work was done on
late Neogene equids from Florida for over 30 years. The simplest
explanation for this was a lack of major new localities. During this
interval attention was primarily focused instead on the very important
early Miocene Thomas Farm Site, and on Pleistocene localities. This
period did see the most intensive (and final) excavations at Mixson's
Bone Bed by Frick field crews. A number of equid specimens were
collected, but the F:AM sample from Mixson's was not studied until
This drought in the study of late Neogene equids was broken by the
discovery in 1962 of the McGehee Farm Site, the first major late
Neogene locality found in north-central Florida since Mixson's.
Equids are moderately diverse at McGehee, although represented mostly
by isolated teeth. Two genera were initially identified (Calippus and
either Pliohippus or Dinohippus) by Webb (1964). These are notable as
the first nonhipparionines reported from the late Neogene of Florida.
Later, three additional equids were listed as members of the fauna
(Hirschfeld and Webb, 1968). The discovery of McGehee was quickly
followed by further new localities with late Neogene equids,
especially the Withlacoochee River sites, the Haile sites, and the
Manatee County Dam Site. The latter produced the first record of
Pseudhipparion (=Griphippus) from Florida (Webb and Tessman, 1967;
1968). Interest was also rekindled in the Bone Valley Region at this
time, with emphasis on collecting in situ material (see Webb, 1969b,
p. 274). The equids from all these sites furnished the basis for
Waldrop's (1971) unpublished thesis, but until very recently have not
appeared in the literature (MacFadden, 1984a; Webb and Hulbert, 1986).
The next major discovery, the Love Site, is certainly the most
important late Neogene vertebrate fossil locality in Florida. For the
first time, material rivaling in quantity and quality the most
productive quarries from the Great Plains was recovered from Florida.
Excavation at the Love Site began in 1974, and continued to June,
1981. Afterwards, there was an almost two year period when its
voluminous equid material was identified, curated and catalogued. The
first report of equids from the Love Site was in Jackson's (1978)
study of Deirochelys. He noted the presence of Leidy's two classic
"Alachua Clays" species, H. plicatile and "Nannippus" ingenuus. Webb
et al. (1981) recognized at least seven taxa of equids in their
preliminary review of the fauna, but oddly did not include either of
the two species recognized by Jackson (1978). More recently, Love
Site equids were studied by Hulbert (1982), MacFadden (1984a), and
Webb and Hulbert (1986), and also provide the major basis for this
In the last 10 years, a number of other studies have investigated
late Neogene Florida equids. MacFadden and Waldrop (1980) described
specimens of Nannippus "phlegon" and proposed a neotype for Nan.
minor. MacFadden (1982) described a new species of Hypohippus from a
lower horizon of the Bone Valley Formation, while Berta and Galiano
(1984) illustrated a tooth of "Astrohippus" martini also from the
lower Bone Valley. MacFadden (1986) referred specimens from the Upper
Bone Valley and from the newly discovered Lockwood Meadows l.f. to
Dinohippus mexicanus and Astrohippus stockii, and discussed their
biochronological significance. The most important locality discovered
subsequent to the Love Site is the Moss Acres Racetrack Site. It was
first worked in December, 1984, and excavated sporadically through at
least 1987. Unlike all the other late Neogene localities in Florida,
specimens from Moss Acres often consist of associated and/or
articulated elements. Equids are diverse at Moss Acres, and many
species are represented by more complete material than at any other
site. The Moss Acres equids are reported here for the first time.
The record of late Neogene mammals, including equids, from the
Texas Gulf Coastal Plain is less complete than that of Florida. How-
ever, they are deposited in traceable stratigraphic units, that can be
placed in direct superposition, thereby aiding correlation. The
earliest studies of Miocene equids from this region are those of Leidy
(e.g. 1869; 1873), but the described specimens are isolated finds.
They are not very important except to generally indicate the age of
the deposits. Increased geological reconnaissance of the region in
the early 1900s resulted in the discovery of several substantial
localities that contained equids (e.g. Cold Spring l.f, and Burkeville
l.f.). Hay (1924) described "Merychippus" francisi from the Noble
Farm Site, but did not compare it with Great Plains forms. Hesse
(1943) first reviewed the biostratigraphic relationships of the faunas
from southeastern Texas. He referred the equids from the Burkeville
and Cold Springs Faunas to "M." francisi and Protohippus perditus.
Quinn (1955) analyzed in detail the nonhipparionine portion of the
Texas Gulf Coastal Plain equids. His study included the faunas previ-
ously known to Hay and Hesse, but also the younger and more productive
Lapara Creek Fauna. Quinn's systematic methodology was highly unorth-
odox, and his work engendered much controversy and criticism (e.g.
Webb, 1969a). The entire equid fauna (including hipparionines) was
restudied by Forsten (1975), whose approach (in terms of alpha-level
systematics) was the diametrical opposite of Quinn's. While he
divided the equids from any particular fauna into many species, she
tended to lump many of these together. In my opinion (as documented
in Chapter 5), the "real" number of species generally lies somewhere
between their two extreme viewpoints. Unlike the situation in
Florida, no major late Neogene localities have been discovered on the
Texas Gulf Coastal Plain in the last 30 years. The differences in
classification of its equids by Quinn (1955), Forsten (1975) and this
study reflect differences in interpretation, and are not based on new
MATERIALS, METHODS AND TERMINOLOGY
Equid crania, mandibles, and isolated teeth of late Barstovian
through Blancan age (excluding Equus, Blancan Nannippus, and
anchitheriines) from the Gulf Coastal Plain of Florida and Texas were
examined and measured. Specimens from major localities and faunas
(e.g. Love Site, Lapara Creek Fauna) were analyzed quantitatively with
univariate statistics. Specimens from this region are principally
housed in the UF, UF/FGS, TMM, TAMU, and F:AM collections. The USNM
and ANSP have a few historically important specimens. In general,
post-cranial elements were not studied, except in the rare instances
when they could be unambiguously assigned to a species. Types or
casts of type specimens of all species known from this period were
examined from the AMNH, ANSP, USNM, TMM, TAMU, UCMP, LACM, PPM, UF,
and UF/FGS collections. Comparative material of equids from outside
of the Gulf Coastal Plain was similarly studied, principally from the
Great Plains but also including specimens from Mexico, Nevada and
California. A primary goal was to obtain data from large quarry
samples of well known faunas, e.g. Burge, Clarendon, Minnechaduza,
Yepomera and Coffee Ranch. These provided standard ranges of
individual and ontogenetic intraspecific variation. In many cases
they also supplied additional information concerning cranial
morphology. Equid skulls are relatively much rarer in the Gulf
Coastal Plain than in the Great Plains, and those present in the
former area are usually crushed or incomplete. The comparative
material was especially useful in associating upper and lower
dentitions of the same species, and in determining character states
for the phylogenetic analysis.
The following systematic procedures were performed for each major
Gulf Coastal Plain equid fauna (i.e. the Cold Spring, Lapara Creek,
Archer and Palmetto Faunas, see Chapter 4). First, each specimen was
assigned to a morphological group. Initially, upper and lower,
juvenile and adult dentitions were all treated separately. Thus for
any fauna, there would be n1 morphs for upper adult dentitions, n2
morphs for upper juvenile dentitions, n3 morphs for lower adult
dentitions, and n4 morphs of lower juvenile dentitions. All the n.'s
were not necessarily the same. Each morph was made up of teeth of
similar size and enamel pattern. The next step was to determine which
morphs merely represented different wear-classes of the same
population. These were matched using sectioned teeth, individuals in
intermediate wear-stages, and measurements of basal crown length (BAPL
and bapl) which are uncorrelated with age. Once this was
accomplished, there were then x, populations represented by upper
adult dentitions, x2 by upper juvenile dentitions, x3 by lower adult
dentitions, and x4 by lower juvenile dentitions. In theory each of
the x.'s should now be the same. In practice, they often differed by
one or two, either because a rare taxon was not represented in all
four groups, or because some populations were still divided into more
than one morph for one or more of the groups. Juveniles were then
paired with the appropriate adult populations using size, morphology,
and, most importantly, older juvenile specimens with erupted first and
second molars. Finally, upper and lower dentitions were paired.
Criteria such as size and relative abundance were used to eliminate
most of the possible combinations. For example, a population with a
mean UTRL of 140 mm could not correspond to a group of lower
dentitions with a mean Itrl of 105 mm. Nor is it likely that a very
rare group based on maxillae would correspond to an extremely common
population based on mandibles (although this is possible in certain
taphonomic sorting regimes). Prior to the discovery of the Moss Acres
Racetrack Site, no associated upper and lower dentitions of Neogene
equids were known from Florida (one mandible from the Withlacoochee
River 4A Site is possibly associated with a maxilla, but there is no
field evidence to substantiate this). Final judgements regarding
pairings were made with associated individuals of related species from
Texas or the Great Plains, or by identifying what genus each morph
represented. For example, if in a fauna there was a group of maxillae
of genus A, and a similar-sized group of mandibles of genus A, then
they were assumed to belong to the same species.
After these steps, for each fauna, most of the specimens could be
placed into one of these populations. A few specimens, either because
they were unworn, or very heavily worn, could not be assigned to a
population. There were also usually a few teeth whose size and
morphology did not quite fall within the range observed in any group.
It is possible that they represented very rare taxa, but unless they
closely matched a well-known species from a contemporary fauna, it was
assumed that they were rare variants of one of the well represented
taxa. It was also assumed that each of these populations from a large
quarry sample or fauna represented a "biological" species.
Once this was accomplished for all faunas, there remained the fol-
lowing systematic problems: what binomen to apply to each population;
and how to determine if populations from two faunas are conspecific or
not? Actually these are identical problems, as one can determine the
proper name of a population by determining with which topotypic sample
it is conspecific. Determining if two, similar, allopatric
populations are conspecific, or if they belong to two closely related
species, or if they only share many primitive traits and are in fact
not especially closely related is not a straightforward procedure.
This is true for modern as well as fossil populations. In my
analyses, I have assumed that geographically and/or chronologically
separated populations can differ significantly from one another, and
still be conspecific. Species boundaries were placed only at
cladogenetic events phylogeneticc branching), or, in instances with no
evidence of branching, at nonarbitrary, punctuated jumps in a chrono-
clinal lineage. This approach differs from that of Gingerich (1985)
and Rose and Bown (1986) who advocated arbitrary division of clinally
evolving lineages. Traditionally, species-level studies of equids
have emphasized the differences between populations, and often each
population from a major fauna has been placed in its own species (see
Dalquest, 1981 for a good example of this). As noted by Mayr (1969,
p. 187), statistically significant differences between allopatric
populations should be taken for granted, and are not justification for
splitting them into separate species. The alpha-level systematic
approach used here usually results in fewer species with much larger
geographic and chronologic ranges than in previous studies.
The phylogenetic interrelationships of equid species and genera
were determined using cladistic methodology (Hennig, 1966; Wiley,
1981). Common ancestry is determined by the distribution of derived
character states among the taxa being studied. Polarity of character
states can be assessed by several methods (Wiley, 1981), of which the
out-group method is among the most widely applied. Character polarity
assessment is a critical step in cladistic analysis, as an error in
judgement can result in a completely false tree. The out-group method
was used here to determine polarities. In this method one or more
taxa that are closely related to but not among the taxa under study
make up an "out-group." Their character states are assumed to be
plesiomorphous. At the present time there is no generally accepted
upon procedure for choosing which of the many possible cladograms best
represents the true evolutionary history of the group. One commonly
used criterion is parsimony (Sober, 1983; Swofford, 1985). The most
parsimonious cladogram (i.e. that with the fewest reversals and paral-
lelisms) is considered optimal by some, although slightly less parsi-
monious cladograms can be more realistic biologically or chronolog-
ically (Clark and Curran, 1986). Moreover, when parallelism among in-
group clades is great, then use of the parsimony criterion may even be
misleading (Gosliner and Ghiselin, 1984). The equid species under
study were subjected to phylogenetic analysis using both a computer
program that generates most parsimonious cladograms (PAUP; Swofford,
1985), and cladograms configured "by hand" (see Chapter 6 for further
details on methods employed in the phylogenetic analysis).
Measurements and Counts
Measurements were primarily taken on individual, adult cheekteeth.
As crania of equids are so scarce from the primary study area, no
attempt was made to take any of the large number of traditional equid
skull measurements (e.g. Osborn, 1912; Eisenmann, 1986). Only
diastema lengths, toothrow lengths and muzzle widths were routinely
measured. Metapodial measurements were taken as described by
Eisenmann (1979). All measurements were taken with dial calipers to
the nearest 0.1 mm. For purposes of quantitative analysis, cheekteeth
were sorted into six categories: P2, P3 or P4, M1 or M2, p2, p3 or
p4, and ml or m2. Third molars were usually not measured, nor were
deciduous teeth. Using the methods of Bode (1931), it is
theoretically possible to identify most isolated cheekteeth as to
exactly where they were positioned on the toothrow, given a large
enough sample of "knowns." However, these procedures are time-
consuming, and do not always result in an unambiguous determination
for each specimen. Moreover, it has not been shown that lumping first
and second molars (for example) in any way adversely affects the
statistical results. In fact, some studies (e.g. Forsten, 1975) have
combined the P3 through M2 into a single class. Six measurements were
taken on each upper cheektooth, and seven on each lower tooth (Figure
1). Except for the basal lengths and crown heights, all measurements
were taken on occlusal surfaces, excluding cement. Altogether about
8000 specimens were measured (5000 upper teeth and 3000 lowers). The
data were stored on CMS files on the University of Florida's (NERDC)
mainframe IBM computer. Statistical computations were done using SAS
sorting and analytical subroutines (SAS Institute Inc., 1985a; 1985b).
Counts of meristic characters were also recorded for individual cheek-
teeth, and form the basis of much of the dental descriptions given in
Stirton (1941) is the standard reference for equid dental termin-
ology. However, the meanings of some terms have recently been changed
to conform to Old World usage. The most important of these, the
structure Stirton (1941) referred to as the protostylid, is now called
the ectostylid. The term protostylid now refers to what Stirton
(1941) called the parastylid. Dental nomenclature employed in this
study is shown in Figure 1. The rudimentary first upper and lower
Figure 1. Schematic occlusal views of upper and lower cheekteeth of
equids demonstrating nomenclature and measurements used in this
study. A. Upper left second premolar (anterior to left, labial up):
1, anterostyle (found on P2s and DP2s only); 2, hypoconal groove; 3,
hypocone; 4, parastyle; 5, mesostyle; 6, metastyle; 7, pli caballin;
8, pli hypostyle; 9, pli postfossette; 10, pli prefossette; 11, pli
protoloph; 12, postfossette; 13, prefossette; 14, prefossette loop;
15, preprotoconal groove; 16, protocone; 17, protoselene. B. Upper
right third or fourth premolar (P34) showing the four measurements
made on the occlusal surfaces of upper cheekteeth: 1, APL, maximum
anterior-posterior length, excluding the ectoloph and hypocone; 2,
TRW, transverse width from mesostyle to lingual-most part of
protocone; 3, PRL, maximum protocone length, excluding spur or
connection to protoselene (if present); 4, PRW, protocone width
perpendicular to PRL. C. Lower left molar (anterior to left, lingual
up): 1, antisthmus; 2, ectoflexid; 3, ectostylid (generally found
only on deciduous teeth in North American taxa); 4, entoconid; 5,
entoflexid; 6, hypoconid; 7, hypoconulid; 9, linguaflexid; 10,
metaconid; 11, metaflexid; 12, metastylid; 13, paralophid; 14, pli
caballinid; 15, postisthmus; 16, protoconid; 17, protostylid. D.
Lower right third or fourth premolar (p34) showing the five
measurements made on the occlusal surface of lower cheekteeth: 1,
apl, maximum anterior-posterior length, excluding protostylid; 2,
atw, anterior width from metaconid to protoconid; 3, ptw, posterior
width from metastylid to hypoconid; 4, mml, metaconid-metastylid
length; 5, entl, length of entoflexid; 8, isthmus, the combined
antisthmus and postisthmus when the ectoflexid is shallow.
cheekteeth are referred to as the DPI and dpi (rather than PI and pl),
as they erupt with the deciduous rather than the permanent premolar
series (Skinner and Taylor, 1967).
Definitions and boundaries of North American Land Mammal Ages
follow the revisions of Tedford et al. (in press). Unless specified
otherwise, ages of Neogene faunas outside the Gulf Coastal Plain are
as determined by Tedford (1981) and Tedford et al. (in press).
Boundaries and subdivisions of Cenozoic epochs follow those of Harland
et al. (1982).
General terms used to describe different ontogenetic phases are
very early (=earliest), early, moderate or middle, and late wear-
stages. Very early wear-stage refers to the period between onset of
wear and the time the occlusal surface is fully worn and reaches its
maximum length. At the end of this stage the tooth retains about 90%
of its original crown height. Early wear-stage refers to the period
after the very early wear-stage until the tooth is worn to about 75%
of its original crown height. Middle wear-stage refers to the period
following the early wear-stage until the tooth is worn to about 25% of
its original crown height. Teeth with less than 25% of their original
crown height are referred to as heavily worn or as being in the late
wear-stage. These arbitrary classes are useful in describing the
changes in enamel pattern associated with wear. When more precise
information is required regarding exactly when during ontogeny a given
event takes place, it will be described in terms of "with x mm of
crown height remaining" or "with x% of original crown height
remaining." The adjective persistent will be used to refer to a
character that appears at the onset of wear and remains visible on the
occlusal surface to at least the end of the moderate wear-stage. A
very persistent character lasts well into the late wear-stage. A
nonpersistent character disappears either during the early wear-stage
or the first half of the moderate wear-stage. When qualitative
characters vary within a population or species, a percentage may be
given to quantify each character state, or terms such as common or
rare may be used. By these I mean that if a sample was chosen
randomly from a population, a very rare character state would be
expected in less than 3% of the sample, a rare character state would
be expected in about 3 to 10% of the sample, a common character state
in about 40 to 75% of the sample, and a usual or very common character
state in about 75 to 90% of the sample.
Ontogenetic and Individual Variation in Equid Cheekteeth
For historical and practical reasons, most of the characters used
in equid systematics (especially at the species level) are those of
the cheekteeth. Historically, many of the first specimens discovered
and described were isolated cheekteeth or maxillary fragments with a
few teeth. These specimens became the name bearers with which all
subsequent material was compared. Practically, at many Tertiary
localities, equid cheekteeth and toothrow fragments are much more
common than skulls, which in many instances are unknown altogether.
Actually, paleontologists studying equids are probably only as guilty
of overemphasizing cheekteeth as many others in their profession, or
only slightly more so. Other characters commonly used in this study
include relative diastema lengths, muzzle width, incisor morphology,
depth of the nasal notch, and the depth and arrangement of the facial
fossae. For Gulf Coastal Plain equids, however, detailed descriptions
of cheekteeth are essential for intraspecific and intrageneric
comparisons. As size and enamel pattern of equid cheekteeth change in
a predictable manner with wear, descriptions of them must include all
Gidley (1901) presented a lucid discussion of both ontogenetic
(wear-related) and individual variation in Equus. He noted
significant changes in enamel complexity and occlusal dimensions as
horse cheekteeth are worn down. He further noted that toothrow length
was strongly affected by the decreasing anteroposterior lengths of the
P3-M2 with wear. Gidley (1901) also showed that intraspecific
variation in features of the enamel pattern was much greater than
previously supposed. Unfortunately, Gidley's study was based on
specimens of domesticated horses (E. caballus), so it did not
necessarily demonstrate natural variation. Even more unfortunately,
authors such as Merriam, Hay and Osborn continued to describe new
species of equids on isolated teeth with little or no regard for the
results of Gidley's study. It took another generation, and studies
such as those of Matthew (1924), Bode (1934) and McGrew (1944b) to
check the flood of new equid species names based on isolated finds.
A detailed account of the enamel morphology of upper and lower
cheekteeth is given for each well represented species in Chapter 5.
Descriptions are divided into groups with similar morphology, e.g. the
Ml and M2. This is because, for most species, certain groups of teeth
can differ not only in size and morphology, but also in the stage of
ontogeny at which a certain morphology may appear (e.g. connection of
the protocone or loss of the pli caballinid). Upper cheekteeth are
divided into three groups for descriptive purposes, P2s, P34s, and Ml-
M3s. In Chapter 5, the following are described for each group with
respect for ontogenetic and individual variation: relative shape and
orientation of the protocone; when (if at all) the protocone connects
to the protoselene; presence/absence of a pli caballin and whether or
not it is bifurcated or multiple; strength and morphology of the
styles; degree of fossette complexity (counts of plications); and
whether or not the hypoconal groove is open. Descriptions of lower
cheekteeth are generally divided into two major classes, premolars
(p2-p4) and molars (ml-m3). In Chapter 5, the following are described
for each group with respect for ontogenetic and individual variation:
presence/absence of a pli caballinid, and whether or not it is
bifurcated or multiple; presence/absence of a protostylid;
presence/absence of plications from the paralophid or isthmus; the
depth, length, and persistence of the ectoflexid, entoflexid,
linguaflexid, and metaflexid; and the relative size, shape, and degree
of separation of the metaconid and metastylid. When available, the
common morphology exhibited by deciduous upper and lower premolars is
also described, but usually in less detail than their permanent
Unworn crown height is an important characteristic of each equid
species. It differs among tooth positions, and is subject to
individual variation as are all size characters. An estimated unworn
crown height (either MSCH or mcch) is given for the P2, P34, M12, p2,
p34, and m12 for each species when available. Estimates rather than
actually measured values are given because complete, unworn but
identifiable teeth are not known for most species. When unworn, the
base of the crown is made of very thin and fragile enamel that is
often broken in otherwise well preserved specimens. Unworn teeth
extracted from crypts usually are not fully formed, and their crown
heights can underestimate the true maximum value by 5 or 10 mm. My
practice was to measure large samples of isolated cheekteeth, and
include in these samples the least worn specimens for which crown
height could be measured. If the specimens with greatest MSCH and
mcch were truely unworn, then their values are given as the estimated
unworn crown height. If, as was typically the case, these specimens
were slightly worn, than a few (two to five, depending on my sub-
jective assessment of their degree of wear) millimeters were added to
their measured crown height to estimate the unworn value. If no
slightly worn (very early wear-stage) specimens for a species are
known, then no unworn crown height is reported. Instead, a maximum
observed crown height is given. For most species, the unworn crown
height estimated for the corresponding upper and lower teeth are equal
or insignificantly different. In order to compare relative unworn
crown height between species of different sizes, a hypsodonty index
(HI) was computed. It is obtained by dividing a species' estimated
M12 unworn crown height by its mean M12 BAPL.
DESCRIPTION OF GULF COASTAL PLAIN EQUID LOCALITIES
Northern Peninsular Florida
Neogene vertebrate fossil localities in northern peninsular Florida
consist of sinkhole and fissure fillings or channel deposits incised
into Eocene limestone. Usually they are geologically isolated from
one another, and sites in close proximity are not necessarily the same
age. The following localities produced the majority of the specimens
from this region that were examined during the course of this study.
Listed for each are its location, associated fauna, age, geology,
previous studies, and what collections) house the fossils produced
there. Localities mentioned in the text that are not described here
produced only a few isolated teeth. The general positions of all
these localities are indicated in Figure 2.
Ashville Site. The Ashville Site (FSM VP loc. JE02) is located in
the SE1/4, sec. 1, T. 2 N, R. 6 E, Ashville Quadrangle, at an exposed
roadcut in Jefferson County. The site was first discovered in 1961
and subsequently collected in 1963. Olsen (1964), citing state
geologist William Yon, described the fossiliferous unit as a clayey,
pebbly, poorly sorted quartz sand with clay stringers, and suggested a
bay or estuary as the environment of deposition. This was suggested
by the transported, fragmentary appearance of the land vertebrates,
and by the presence of marine vertebrates (sharks and rays) in the
Figure 2. 0Map of northern and central peninsular Florida (between
27 and 30 N) depicting approximate locations of fossil sites
mentioned in the text. Late Barstovian and early Clarendonian: A,
Phosphoria Mine, Polk Co. Early Clarendonian: A, Hookers Prairie
Mine, Polk Co. Very late Clarendonian: B, Love Site, Alachua Co.
Late Clarendonian or early Hemphillian: C, Coffrin Creek, Alachua
Co.; C, VA Hospital Site, Alachua Co.; D, Nichols Mine, Polk Co.
(other ages too); E, Peace River near Gardner, Hardee Co.; F, Cummer
Mine, Gilchrist Co. Early Hemphillian: F, Haile Sites 5B and 19A,
Alachua Co.; F, McGehee Farm Site, Alachua Co.; G, Mixson's Bone Bed,
Levy Co.; H, Moss Acres Racetrack Site, Marion Co. Late early
Hemphillian: I, Withlacoochee River Sites 4A and 4X, Marion-Citrus
county line; J, Manatee Dam Site, Manatee Co.; K, L, Dunnellon
Phosphate Mine sites, Marion and Citrus Co. Late Hemphillian: M,
Lockwood Meadows, Sarasota Co.; N, Bone Valley Region (within general
outline), Polk and adjacent counties; 0, SR64 Site, Manatee Co.; P,
Kissimmee River 6, Okeechobee Co. Late Blancan: M, Macasphalt Shell
Pit, Sarasota Co.; F, Haile 15A, Alachua Co.
same deposit. Olsen (1964) included the following in the fauna:
Merychippus sp., Diceratherium sp., and indeterminant large and small
artiodactyls. Based on the stage of evolution of the horse teeth,
Olsen suggested an age intermediate between those of the lower Snake
Creek and lower Valentine Faunas in Nebraska. As currently perceived,
this would be early late Barstovian (about 14 ma). Tedford and Hunter
(1984) suggested a slightly younger age (about 13 ma), and a general
correlation with the Cold Spring Fauna of Texas. Vertebrate remains
from Ashville consist primarily of isolated teeth. These are poorly
preserved and often crushed, making identifications uncertain.
Specimens are in the UF/FGS collection.
Love Site. The Love Site (or Love Bone Bed; FSM VP loc. AL01) is
located in the NW1/4, SW1/4, NW1/4, sec. 9, T. 11 S, R. 18 E, Archer
Quadrangle, Alachua County. It was discovered as the owner of the
property, Ron Love, tilled his okra crop in 1974. Subsequent
excavations by FSM personnel revealed a complex fluvial deposit
incised to a depth of 4 m in the Eocene limestone bedrock (Webb et
al., 1981, provide a detailed discussion of the geology of the site).
Over 80 taxa of vertebrates from a variety of paleoenvironments were
recovered, and these are represented by thousands of specimens. Taxa
previously studied include pond turtles (Jackson, 1976; 1978), a heron
(Becker, 1985a), an osprey (Becker, 1985b), a vulture (Becker, 1986),
a dromomerycid (Webb, 1983), a tapir (Yarnell, 1980), canids (Baskin,
1980b), a felid (Baskin, 1981), a nimravid (Baskin, 1981), procyonids
(Baskin, 1982), a mylagaulid (Baskin, 1980a), and a cricetid rodent
(Baskin, 1986). Major elements of the fauna that are as yet unstudied
include the fish, tortoises, amebelodontine gomphotheres, rhino-
ceratids, camelids, tayassuids, and the remainder of the rodents.
Although many of the vertebrates are similar, even conspecific, with
those from Mixson's Bone Bed and McGehee Farm, a slightly older,
latest Clarendonian age is suggested for the Love Site (Webb et al.,
1981). The site lacks all of the early Hemphillian indicator taxa of
Tedford et al. (in press), and detailed study of traceable lineages
strongly suggest that Love Site populations display more primitive
characters than those from Mixson's or McGehee. The best correlative
of the Love Site from the Great Plains is the very late Clarendonian
Xmas-Kat Fauna of Nebraska (Skinner and Johnson, 1984). Specimens are
in the UF collection.
McGehee Farm Site. McGehee Farm (FSM VP loc. AL27) is located in
the southern half of the NE1/4, sec. 22, T. 9 S, R. 17 E, Newberry
Quadrangle, Alachua County. Hirschfeld and Webb (1968) described the
sediments as phosphatic sand and gravel deposited over the eroded
surface of the Ocala Limestone, and interpreted the environment of
deposition as estuarine. In addition to equids, the mammalian fauna
includes sloths (Hirschfeld and Webb, 1968; Webb, in press), canids
(Webb, 1969b), a mylagaulid (Webb, 1966), Synthetoceras (Patton and
Taylor, 1971), camelids, rhinos, Tapirus (Yarnell, 1980), and
amebelodontine gomphotheres. An early Hemphillian age is indicated by
the presence of sloths (Marshall et al., 1979; Tedford et al., in
press), and the stage of evolution of the canids, equids, camelids,
and rhinos. Specimens are in the UF collection.
Haile 19A Site. Haile 19A (FSM VP loc. AL34) is located in the
NW1/4, SE1/4, NE1/4, sec. 26, T. 9 S, R. 17 E, Newberry Quadrangle,
Alachua County. It very possibly represents the same depositional
system as the sedimentologically similar nearby McGehee Farm Site.
The Haile 19A vertebrate fauna is predominantly comprised of sharks,
teleost fish, and Gavialosuchus. Terrestrial vertebrates are
relatively rare and consist primarily of isolated, durable elements
like teeth. The mostly unstudied mammalian fauna includes Epicyon
validus, Pliometanastes, Aphelops, Pediomeryx hamiltoni, and
Procamelus, as well as a diverse equid fauna. The fauna most closely
resembles those from McGehee and Mixson's, and indicates an early
Hemphillian age. Several other of the Haile sites have produced late
Miocene vertebrates, but of these Haile 19A is the most productive.
Specimens are in the UF collection.
Mixson's Bone Bed. Mixson's (FSM VP loc. LV09) is located in the
NE1/4, SW1/4, sec. 29, T. 12 S, R. 19 E, Williston Quadrangle, Levy
County. The site represents a massive clay-filled sinkhole. The
vertebrate fauna was initially described by Leidy in a series of short
papers from 1884 to 1890, and summarized by Leidy and Lucas (1896).
The site was extensively excavated in the late 1930s and early 1940s
by Frick field crews, who amassed much more complete material than
earlier workers, and made several additions to the fauna. The F:AM
material has only been partially described (Webb, 1969b; 1983; in
press; MacFadden, 1984a; Harrison and Manning, 1983; Harrison, 1986),
and no up-to-date faunal list has been published. Biochronologically
important taxa present are Thinobadistes segnis (Hay, 1919; Webb, in
press) and Epicyon validus (Webb, 1969b; generic assignment follows
Baskin, 1980b); they both indicate an early Hemphillian age.
Specimens are in the USNM, F:AM and UF/FGS collections.
Moss Acres Racetrack Site. Moss Acres (FSM VP loc. MR12) is
located in the NW1/4, NE1/4, sec. 11, T. 14 S, R. 19 E, Morriston
Quadrangle, Marion County. It was discovered in December, 1984,
during the construction of a practice racetrack for thoroughbred
horses. Geologically and topographically it resembles the descrip-
tions for Mixson's given by Leidy and Lucas (1896). The sediments are
a massive bluish-green clay filling a depression in the limestone.
Vertebrate remains were found only in a limited region of about 50 m
by 25 m. Even within this area fossils were scarce relative to other
Florida sites. Although some isolated elements and teeth were found,
many specimens consist of associated or articulated bones. Usually
these were limbs or strings of vertebrae, although some partial
skeletons, and associated skulls and skeletons were recovered.
Preservation is typically excellent, although skulls and other fragile
elements are badly crushed. The entire vertebrate fauna as known
through April 1987 is listed in Table 1. Most common is the long-
legged rhino Aphelops, represented by about ten skulls or palates.
The fauna indicates a slightly but significantly younger age than
Mixson's or McGehee, the gomphothere, Aphelops, Pediomeryx,
Neohipparion, Nannippus and Calippus all being represented by more
progressive species. The stage of evolution of the horses suggests a
slightly older age than the Withlacoochee River 4A site. An early
Table 1. Preliminary list of the vertebrate fauna from the Moss
Acres Racetrack Site, Alachua Formation, Marion County, Florida
(early Hemphillian, about 7.0 to 7.5 ma).
Famf1"T - y dae
Hipparion sp., cE. H. tehonense
Campus maccartyi n. sp.
very small equid, gen. indet.
Family Tayassuidae, gen. indet.
"Hemiauchenia" sp., cf. "H." minima
Fami ly Dromomerycidae
Pediomeryx n. sp. (?)
Family Gelocidae, gen. indet.
Amebelodon n. sp., near A. fricki
Hemphillian age of about 7.0 to 7.5 ma seems to best fit the currently
available data. Specimens are in the UF collections.
Withlacoochee River Site 4A (= With 4A). With 4A (FSM VP loc.
MR02) is located in the Withlacoochee River in the NW1/4, NW1/4, sec.
30, T. 17 S, R. 20 E, Stokes Ferry Quadrangle, on the Marion-Citrus
county line. Like Mixson's and Moss Acres, this site is a massive
clay deposit filling a sinkhole (Webb, 1969b). Besides equids, the
mammalian fauna includes Indarctos (Wolff, 1978), Machairodus,
Osteoborus (Webb, 1969b), Enhydritherium (Berta and Morgan, 1985),
Pliometanastes (Hirschfeld and Webb, 1968), Thinobadistes (Webb, in
press), and Hexameryx (Webb, 1973). Becker (1985a) reported a new
species of heron from With 4A, and reviewed the site's age (also see
Berta and Morgan, 1985). The co-occurrence of Indarctos and
Machairodus is limited to the brief late early Hemphillian interval (6
to 7 ma), according to Tedford et al. (in press). The horses also
suggest an intermediate age between the well known faunas of the
"Alachua Clays" to the north and the Upper Bone Valley Fauna to the
south. Specimens are in the UF collection.
Withlacoochee River Site 4X (= With 4X). With 4X (FSM VP loc.
MR24) is also located in the Withlacoochee River in the NE1/4, NW1/4,
sec. 30, T. 17 S, R. 20 E, Stokes Ferry Quadrangle. Depositionally
identical to With 4A, the fauna of With 4X is less diverse but does
include several well preserved horse teeth, a progressive species of
Thinobadistes (Webb, in press), and a large Aphelops. They indicate a
Hemphillian, probably late early Hemphillian age. Specimens are in
the UF collection.
Southern Peninsular Florida
Neogene vertebrate deposits in southern peninsular Florida are
found in more widespread geologic horizons than those in the north,
particularly in the area known as the Bone Valley Region. Numerous
ephemeral exposures created by large-scale phosphate mining in this
900 km2 region have long produced vertebrate fossils. Along the
southwest coast of Florida, seaward extensions of the Bone Valley
Formation are sometimes encountered and may produce vertebrate fossils
as well. The general locations of these are indicated in Figure 2.
Bone Valley Region. The Florida State Museum has specimens from
dozens of vertebrate-bearing localities from this region on file.
Early studies of the area's vertebrates (e.g. Sellards, 1910; 1916;
Simpson, 1930) usually considered them a cohesive fauna of
approximately the same age as Mixson's Bone Bed. In the 1960s, FSM
personnel began precise stratigraphic studies of the Bone Valley.
Over the last twenty years, an increasingly clearer and more complex
geologic history has emerged for the region. A definitive
biostratigraphic summary is planned (Waldrop and Webb, in prep.). For
now, at least six distinct vertebrate faunas are recognized from the
Bone Valley Formation, with ages of: early Barstovian; early late
Barstovian; late Barstovian; latest Barstovian-earliest Clarendonian;
late Clarendonian-early Hemphillian; and very late Hemphillian
(MacFadden and Webb, 1982; Webb and Crissinger, 1983; Berta and
Morgan, 1985; MacFadden, 1986; Webb and Hulbert, 1986). In addition
to these, the underlying Hawthorn Formation has produced earliest
Barstovian vertebrates (A. E. Pratt, pers. comm.), and the overlying
sand and gravel beds contain fossils of Pleistocene age. Obviously,
specimens of unknown stratigraphic provenience from the region are not
necessarily the same age. In situ vertebrate concentrations
discovered by David Webb, John Waldrop and Don Crissinger now permit
the determination of natural faunal
with most of the older collections,
stratigraphic context and contained
faunal terms used below are not yet
previously used by Webb and Hulbert
approximately contemporaneous small
The Bradley Fauna is represented
Kingsford and Nichols Mines in Polk
assemblages. This was impossible
as they were recovered out of
temporally mixed assemblages. The
formally named, but were
(1986) to collectively refer to
local faunas and isolated finds in
only by a few localities from the
County southwest of Mulberry. The
age of this fauna is late, but not latest, Barstovian based on the
presence of Gomphotherium calvertensis, Procranioceras sp., cf. P.
skinneri, and horses such as Pro. perditus and Megahippus sp.
Stratigraphically, the fauna originates from sediments underlying
those producing the Agricola Fauna in at least one section of the
Kingsford Mine (Waldrop and Webb, in prep.). The equid component of
the Bradley Fauna contains less progressive taxa than the lower
Agricola Fauna (Red Zone), and indicates general biochronological
correlation with the upper Burkeville Fauna of Texas, the Norden Dam
l.f. of Nebraska, and the Pawnee Creeks Fauna of Colorado.
The Agricola Fauna is known from a number of mines in the region,
including the Nichols, Kingsford, Hookers Prairie, Silver City,
Brewster Haynesworth, and Phosphoria mines. It is best represented
from the latter, where modest in situ collections were made by John
Waldrop and associates in the late 1970s, and subsequently transferred
to the UF collection. The Phosphoria section has two distinct,
stratigraphically superposed assemblages that both belong in the
Agricola Fauna. The lower unit, the Red Zone, compares most favorably
with the Cold Spring Fauna of Texas and the Devil's Gulch Fauna of
Nebraska. The overlying Grey Zone correlates best with the Lapara
Creek Fauna of Texas and the Burge Fauna of Nebraska. The suggested
age for the Agricola Fauna is thus late Barstovian through earliest
Clarendonian. As the evidence rests almost entirely on its equid
fauna, its age will be further discussed in Chapters 5 and 7.
Pliocyon robustus Berta and Galiano (1984) is also a member of this
Unlike the other faunas, the third late Neogene terrestrial verte-
brate assemblage recognized in the Bone Valley Region is represented
by isolated elements recovered without stratigraphic context relative
to the others. The most productive source for this fauna in the Bone
Valley are regions in the Nichols Mine where Donald Crissinger
(geologist for Mobil Chemical Company) collected about 75 specimens
from a "stream matrix." These specimens are uniformly preserved (the
enamel is a light grey), and appear to represent a cohesive fauna
intermediate in age between the Agricola and Palmetto Faunas. The
equids are conspecific with those of the Love, McGehee and Mixson's
localities, and together these sites are all referred to as the Archer
Fauna (Webb and Hulbert, 1986).
The Palmetto or Upper Bone Valley Fauna is the most widespread and
abundant in the region. In situ collections of this fauna are known
from the Palmetto, North Palmetto, Kingsford, Nichols, Gardinier, and
Payne Creek mines. A very late Hemphillian (about 5.0 to 4.5 ma) age
is indicated by the combined presence of Megalonyx curvidens,
Hexameryx simpsoni (Webb, 1973), advanced Teleoceras, Agriotherium
schneideri (Sellards, 1916), Megantereon hesperus (Berta and Galiano,
1983), Felis rexroadensis (MacFadden and Galiano, 1981), Plesiogulo
marshall (Harrison, 1981), Enhydritherium terraenovae (Berta and
Morgan, 1985), and Osteoborus dudleyi (Webb, 1969b). The equid fauna
also supports this age assignment (MacFadden, 1986; Chapter 7). The
Palmetto Fauna's vertebrates represent a diverse suite of marine,
estuarine, freshwater and terrestrial habitats (Berta and Morgan,
1985). The Upper Bone Valley Formation consists of a complex of
channel deposits, often with coarse phosphatic gravel lag deposits,
fining upwards into unconsolidated beds of sand and clay (Webb, 1981;
Webb and Crissinger, 1983). These are interpreted as deltaic-fluvial
environments that drained into estuarine and nearshore marine habitats
when sea level stood about 50 m higher than at present (MacFadden and
Webb, 1982; Webb and Crissinger, 1983). Equids are primarily
represented in the Palmetto Fauna by isolated cheekteeth, and these
durable elements make up a high percentage of the terrestrial
vertebrate specimens. Partial mandibles and post-cranial elements of
equids are uncommon; maxillae are very rare. To date, one partial
equid skull (of Nannippus minor, UF 67000) has been recovered from the
fauna. Unfortunately, it lacks the diagnostic facial region and is
badly crushed. However, it at least suggests a potential for further
discoveries of more complete specimens. Equids from the Palmetto
Fauna examined during the course of this study are from the UF,
UF/FGS, TRO, AMNH, F:AM, and UCMP collections.
Manatee County Dam Site. The Manatee Dam Site (FSM VP loc. MA10)
is located in sec. 30, T. 34 S, R. 20 E, Verna Quadrangle. The
geology of the site was described by Webb and Tessman (1968), who also
presented a geologic section. Based on the site's sedimentology, they
concluded that it represents a westward extension of the Bone Valley
Formation. The mammalian fauna includes (besides equids) camelids,
Teleoceras, Tapiravus, and Rhynchotherium (Webb and Tessman, 1967;
1968). These suggest a Hemphillian age for the fauna. The low
elevation of the site implies that deposition occurred at a period
when sea level was as low as the present. This suggests an older age
than the Palmetto Fauna, which was deposited during the very early
Pliocene when sea level was substantially higher than the present
(Harland et al., 1982). The presence of Pseud. skinneri (Webb and
Hulbert, 1986) and Calippus (Chapter 5) also indicates an older age,
probably late early Hemphillian, approximately equivalent to that of
With 4A. Specimens are in the UF collection.
Lockwood Meadows Site. Lockwood Meadows (FSM VP loc. S004) is
located in the NW1/4, NW1/4, sec. 16, T. 36 S, R. 18 E, Sarasota
Quadrangle, Sarasota County. It is primarily a marine vertebrate
fauna that was recovered from a phosphatic gravel deposit.
Terrestrial vertebrates are represented by isolated, usually waterworn
or fragmentary elements. The fauna includes several equids, a
camelid, a rhino, a gomphothere, a mammutid, and cetaceans (MacFadden,
1986; MacFadden and Mitchell, in prep.), and has been assigned a late
Hemphillian age. Specimens are in the UF collection.
Macasphalt Shell Pit. The Macasphalt Shell Pit (FSM VP loc. S007)
is located in the SW1/4, sec. 12, T. 36 S, R. 18 E, Bee Ridge
Quadrangle, Sarasota County. The quarry has been known by at least
three names, the Warren Brothers, Macasphalt and APAC Shell Pit. Two
different horizons exposed by quarrying operations at Macasphalt
produce vertebrate fossils. Low in the quarry, marine vertebrates,
including mammals, are found in the Tamiami Formation. The other
vertebrate-bearing horizon in the quarry is a thin unit in the
overlying Pinecrest beds. It is this latter horizon, Unit 4 of Petuch
(1982), that has produced equids, and other, locally concentrated ver-
tebrate remains. When abundant, they consist primarily of Siren,
water snakes, turtles, Alligator, many species of fish, and aquatic
birds. Terrestrial mammals are relatively much rarer, but 22 taxa
identifiable to at least the family level are known (Morgan and
Ridgeway, in press). Nineteen of these have been collected in situ
from Unit 4 by FSM personnel, and appear to represent a temporally
unmixed fauna. Biochronologically important mammals recovered from
Unit 4 are Nannippus peninsulatus, advanced Equus sp. (not
Dolichohippus), Dasypus bellus, Holmesina floridana, Megalonyx lepto-
stomus, Glossotherium chapadmalense, Neochoerus dichroplex, Sigmodon
minor, Mylohyus floridanus, and Trigonictus sp. Co-occurrence of
these taxa indicates a late Blancan (about 3.0 to 2.0 ma), latest
Pliocene age for Unit 4 (Marshall et al., 1979; Tedford, 1981; Galusha
et al., 1984), postdating the formation of the Panamanian land bridge
that connected North and South America. Stanley (1986; pers. comm.),
however, dates the entire Macasphalt section as early Pliocene (>3.0
ma) based on biochronologic ranges of selected bivalve taxa.
Multidisciplinary efforts to resolve this conflict and to date this
section using micropaleontological and geochemical techniques are
currently underway by Florida State Museum personnel.
Texas Gulf Coastal Plain
Scattered vertebrate fossils have been reported from the Texas Gulf
Coastal Plain for over a century. Wilson (1956) summarized previous
geologic interpretations, and recognized three Neogene lithostrati-
graphic units (the Oakville, Fleming and Goliad Formations) that have
produced vertebrates. They outcrop in narrow bands that run roughly
parallel to the present coastline (see Quinn, 1955, Figure 5 or
Patton, 1969, Figure 1). Wilson (1956) recognized four principal
vertebrate faunas in these three formations; these are, from oldest to
youngest, the Garvin Gully, Burkeville, Cold Spring and Lapara Creek
Faunas. He used the term "fauna" to indicate a group of local faunas
of similar composition found in the same stratigraphic unit. The
Hemingfordian Garvin Gully Fauna is excluded from this study by its
early age. Estimates of the ages for the other three faunas have
varied greatly (Hesse, 1943; Stenzel et al., 1944; Quinn, 1955;
Wilson, 1956; Patton, 1969; Patton and Taylor, 1971; Forsten, 1975;
Slaughter, 1981; Tedford and Hunter, 1984; Tedford et al., in press).
The Burkeville Fauna of Wilson (1956) contains a number of local
faunas which date from the early Barstovian (about 16 ma) to the early
late Barstovian (about 13.5 ma), a considerable period of time during
which significant changes occurred in the equid fauna. As this study
is limited to equids from the late Barstovian through Hemphillian,
only material from the younger local faunas of the Burkeville Fauna
was studied in detail. This excludes the Point Blank, Moscow, and
Trinity River local faunas, but not the Burkeville l.f. In fact, the
equids from the Burkeville l.f. much more closely resemble those of
the Cold Spring Fauna than they do those of the older Point Blank or
Trinity River sites. The Burkeville l.f. is of early late Barstovian
age, equivalent to the Pawnee Creeks Formation sites in Colorado and
some of the lower faunas of the Valentine Formation in Nebraska
(Tedford et al., in press). This correlation is based on the presence
of Anchitheromys and Proboscidea (Tedford and Hunter, 1984; Reinhardt,
1976). The overlying Cold Spring Fauna is also comprised of a number
of local faunas. They are thought to transcend the later part of the
late Barstovian (13.5 to 12.0 ma; Tedford et al., in press). The
equids from these local faunas are generally similar, and the material
is not adequate to document detailed microevolutionary changes. The
Cold Spring Fauna is similar in age to, and contains many of the same
equids as, the Devil's Gulch Fauna of Nebraska.
The Lapara Creek Fauna is derived from more southerly exposures
that stratigraphically overlie Burkeville and Cold Spring equivalents
(Wilson, 1956). Tedford et al. (in press) divide this fauna into two
units, citing evidence of significant in situ species-level evolution
of the equids. Forsten (1975) found no such differences, and my
examinations also do not support such a major division. I therefore
treat the entire fauna as a single sample for purposes of quantitative
analyses. I do follow Tedford et al. (in press) in their age
assignment for the Lapara Creek Fauna (earliest Clarendonian),
intermediate between the Burge and Clarendon Faunas. Texas Gulf
Coastal Plain equids studied during the course of this project are in
the TMM, TAMU and F:AM collections.
Order Perissodactyla Owen, 1848
Family Equidae Gray, 1821
Subfamily Equinae Steinmann and Dbderlein, 1890
Type genus. Equus Linnaeus, 1758.
Included taxa. Archaeohippus Gidley, 1906b; Parahippus s.l.
Leidy, 1858 (including Desmatippus Scott, 1893); "Parahippus"
leonensis Sellards, 1916; "Merychippus" gunteri Simpson, 1930;
"Merychippus" primus Osborn, 1918; Hipparionini Quinn, 1955; and
Equini Quinn, 1955.
Revised diagnosis. Equids with relatively elongated facial
regions; orbit posteriorly placed relative to toothrow (anterior
margin dorsal to M3 or entirely posterior to M3); labial cingulum on
permanent upper cheekteeth vestigial or absent; metaloph usually
plicated; lateral metapodials tightly bound to median metapodial, not
able to move independently; relatively elongate first medial phalanx
with strong oblique scar for ligament attachment; shaft of ulna very
reduced; fibular shaft vestigial.
Discussion. The Subfamily Equinae traditionally includes only the
horizontal grade "Merychippus" and its "descendants," the hippar-
ionines and equines (e.g. Simpson, 1945). In this arrangement,
Archaeohippus and Parahippus are placed in the Anchitheriinae. This
classification is paraphyletic, and does not represent a natural
phylogenetic grouping. Matthew (1926 and especially 1932) first
noted the number of progressive (relative to Mesohippus and anchi-
theriines) post-cranial features shared by Parahippus, Archaeohippus,
and advanced equids. He concluded that the two should be grouped
with the protohippines rather than the anchitheriines. These post-
cranial characters were further documented, and this classification
was also advocated by Sondaar (1968, pp. 63-65). The features noted
by these two authors were used to compile the revised diagnosis.
Tribe Hipparionini Quinn, 1955
Calippini Quinn, 1955, p. 27 (in part).
Type genus. Hipparion de Christol, 1832.
Included North American genera. Pseudhipparion Ameghino, 1904;
Neohipparion Gidley, 1903; Merychippus s.s. Leidy 1857; Nannippus
Matthew, 1926; Cormohipparion Skinner and MacFadden, 1977.
Revised diagnosis. Tridactyl equids with well cemented,
subhypsodont to hypsodont cheekteeth and well formed fossettes.
Differ from equines and protohippines by having much better separated
metaconids and metastylids (except for Equus and progressive species
of Protohippus); protocone usually isolated from protoselene until at
least middle wear-stage; and fossette borders more persistently and
usually more complexly plicated.
Discussion. In addition to the advanced genera commonly
recognized as hipparionines (e.g. MacFadden, 1984a), I include
Pseudhipparion and "Merychippus" in the tribe. Chapter 6 details the
phylogenetic relationships among hipparionine genera, and documents
synapomorphies used to support their inclusion in the tribe. Hippar-
ionines are a monophyletic group (Forsten, 1982; 1984), not a para-
phyletic assemblage (MacFadden, 1984a). Their first appearance is
late Hemingfordian (about 17 ma). Skinner et al. (1977, p. 343)
recognized two primitive populations in the Sheep Creek Fauna of
Nebraska as "Merychippus insignis tertius (Osborn)" and "Merychippus
isonesus quintus (Osborn)." Hemingfordian and Barstovian species of
hipparionines have traditionally been referred to the grade
"Merychippus." I restrict usage of this name to the population
described by Skinner and Taylor (1967) from Echo Quarry as M.
insignis, and a very limited number of species (see Chapter 6).
Evander's (1986) suggestion that the genoholotypic specimen of
Merychippus is diagnostically inadequate deserves serious consi-
deration. Unfortunately, there is no readily available replacement
name, nor did Evander suggest one for this limited monophyletic group
of Barstovian species. I therefore refer to it as Merychippus s.s.
The alpha-level systematics of North American hipparionines were
greatly clarified by MacFadden (1984a). There are some differences
between his interpretations and mine, but for the most part these are
based either on new material unavailable to him (e.g. Moss Acres); on
the Love Site material, which he purposefully did not examine in
great detail; or on previously unstudied material that I found
uncatalogued in the F:AM and UCMP collections.
Genus Neohipparion Gidley, 1903
Neohipparion GIDLEY, 1903, p. 467.
Hesperohipparion DALQUEST, 1981, p. 506
Type species. Neohipparion whitney Gidley, 1903 (now considered a
junior synonym of Neo. affine (Leidy), 1869).
Included species. Neo. trampasense (Edwards), 1982; Neo. leptode
Merriam, 1915a; Neo. eurystyle (Cope), 1893; Neo. gidleyi Merriam,
Revised diagnosis. Medium to large-sized hipparionines with
poorly developed, shallow, unrimmed DPOF, or lacking DPOF.
Protocones elongate-oval or very elongated; isolated to near base of
crown except in P2. Well developed pli caballinids on p2-p4 and dp2-
dp4 (and on ml-m3 of advanced species) that often extend further
labially than the base of the protoconid or hypoconid; relatively
elongated and well separated metaconids and metastylids; labial
borders of protoconid and hypoconid flattened; ectostylids weakly
developed or absent on deciduous premolars. Slender metapodials.
Discussion. Gidley (1903) based Neohipparion on the superb type
skeleton of Neo. "whitneyi" (AMNH 9815), at the time the most
completely known hipparionine individual. He included most of the
previously described North American species of "Hipparion" in his new
genus, in what was probably the first attempt to classify these
horses phylogenetically. Gidley (1903; 1907) used both facial and
dental characters to distinguish Neohipparion from Hipparion, a very
modern approach. Except for Merriam (e.g. 1915a), most other authors
did not recognize Neohipparion as a distinct genus until 1935.
However, it was often used as a subgenus of Hipparion, even though
the two were thought to have separate merychippine origins (Matthew
and Stirton, 1930, p. 356). Beginning in 1935, Stirton and McGrew
began to separate Neohipparion and Nannippus at the generic level
from Hipparion (Stirton and McGrew, 1935; McGrew, 1938; Stirton,
1940), and its generic status has seldom been questioned since
(Forsten, 1982, is an exception, but she has subsequently  used
it as a valid genus).
Traditionally, two species-groups comprise Neohipparion: one
composed of the predominantly Clarendonian taxa Neo. affine (= Neo.
whitneyi), Neo. coloradense, and Neo. occidentale; and the other of
the Hemphillian species Neo. leptode, Neo. eurystyle, Neo.
phosphorum, Neo. gidleyi, and a number of Mexican species named by
Stirton (1955) and Mooser (1960; 1964). Neo. occidentale is referred
to a separate genus, Cormohipparion, based on its deep DPOF, deep
ectoflexids, rounded protoconid and hypoconid labial borders, and
strong dp ectostylids (Skinner and MacFadden, 1977). "Neo."
coloradense is here recognized as the sister-taxon to Neohipparion
and Pseudhipparion, and thus cannot be placed in either genus
(Chapter 6). Thus, of the first species-group, only the genotype is
still considered a valid member of Neohipparion. It has long been
recognized that Neo. affine is less progressive in many of its dental
features than other members of the genus (Stirton, 1940; MacFadden,
1984a). This morphologic gap led Dalquest (1981) to formally
separate the Neo. eurystyle species-group as a distinct genus,
Hesperohipparion. Apparently unknown to Dalquest, there then existed
an undescribed population of late Clarendonian and early Hemphillian
Neohipparion morphologically and chronologically intermediate between
the two species-groups. It was formally described by Edwards (1982)
as Hipparion trampasense. MacFadden (184a) transferred it to
Neohipparion and illustrated cranial material of this new species.
Thus Dalquest's Hesperohipparion is unnecessary, and its use would
render Neohipparion either paraphyletic or monotypic.
Neohipparion affine (Leidy), 1869
Hipparion affine LEIDY, 1869, p. 286; OSBORN, 1918, p. 178.
Hippotherium occidentale (Leidy), COPE, 1889, p. 434 (in part).
Neohipparion whitneyi GIDLEY, 1903, p. 467.
Neohipparion affine (Leidy), GIDLEY, 1903, p. 467; GIDLEY, 1907,
p. 887-888; STIRTON, 1940, p. 183; MACFADDEN, 1984a, p. 90.
Hipparion (Neohipparion) affine Leidy, MATTHEW and STIRTON,
1930, p. 362.
Equus laparensis QUINN, 1955, pp. 58-60 (in part).
Equus sp. or Neohipparion sp., QUINN, 1955, p. 62.
Neohipparion occidentale (Leidy), FORSTEN, 1975, pp. 65-69 (in
Type specimen. USNM 584, five apparently associated upper
Type locality. Exact locality unknown, "from the Niobrara River"
region according to Leidy (1869). Skinner et al. (1977) provided
evidence that the type locality might be Porcupine Butte, South
Stratigraphic occurrence and age of type locality. Probably
Ogallala Group; Clarendonian, about 9.5 to 11.5 ma.
Distribution. Very late Barstovian to late Clarendonian of the
Great Plains; early Clarendonian of the Texas Gulf Coastal Plain;
possibly Clarendonian of Oregon.
Referred Gulf Coastal Plain specimens. Lapara Creek Fauna (see
Quinn, 1955 and Wilson, 1956). Bridge Estate Site, Bee Co., TX: TMM
31132-432 R P34; -616 R M12; Buckner Ranch Site, Bee Co., TX: TMM
30896-572 L P34; -571, -395 2 L M12; -576, -577 2 R P2; -578, -579 2
L P2; -392 L M3; -480 R mandible with p2-m3 (Quinn, 1955, Plate
14.5); -454 R p34 (Quinn, 1955, Plate 14.3); -573, -574 2 L p34; -580
Revised diagnosis. Larger than Neo. trampasense or Neo.
eurystyle, toothrow lengths about 135 to 150 mm. Unworn M12 MSCH
about 56 mm, thus less high crowned than all other species of
Neohipparion. Relatively simple fosettes; pli caballin single; pli
caballinid prominent only on slightly worn p2-p4 only. Shallow,
poorly developed DPOF posteriorly includes large lacrimal bone.
Description. Neohipparion affine is a large species of
Neohipparion with a distinct, shallow, unrimmed DPOF on the lacrimal,
nasal and maxillary bones (Osborn, 1918, Plate 32.1). Its upper
cheekteeth are characterized by elongate-oval, narrow protocones,
rarely with protoconal spur; relatively simple fossettes; and wide
hypoconal groove open to the base of the crown (Fig. 3A). The upper
premolars have large, broad, usually single plicaballins; they are
generally smaller and less persistent in molars. Fossette plications
are simple, not bifurcated. The pli protoloph is absent or single,
except in the P2 where 39% (n=19) have two loops. The posterior half
of the prefossette usually has a long prefossette loop, and one to
four small, simple plications. The anterior half of the postfossette
usually has only two or three plications. A pli hypostyle is
generally either absent (35% of premolars, 53% of molars) or single
(64% of premolars, 43% of molars). In earliest wear-stages, the
lower premolars have very shallow ectoflexids and well developed pli
caballinids (Fig. 3B); with wear the ectoflexid rapidly deepens and
the pli caballinid gradually disappears. The latter usually occurs
near the beginning of the moderate wear-stage, much earlier in
ontogeny than in other species of Neohipparion. AMNH 9815 holotypee
of Neo. whitneyi, Osborn, 1918, Fig. 144) is an example of the usual
morphology of moderately worn lower cheekteeth. Pli caballinids are
rare on molars, and then only found in early wear-stages and are
rather small (e.g. TMM 30896-480). A distinctive generic character
are the flattened bases of the hypoconid and protoconid, especially
evident on the premolars. The protoconid and hypoconid of the molars
may retain the primitive rounded state, or have flattened bases. In
early wear-stages, the isthmus of the lower premolars is often pli-
cated, but there are no well developed plications extending poster-
iorly from the paralophid. Ectostylids of deciduous premolars are
very reduced. Crown heights of very slightly worn teeth are 4043 mm
for P2s, 48-51 mm for P34s, 55-58 mm for M12s, and 54-56 mm for ml2s.
Discussion. The Lapara Creek specimens listed above are referred
to Neo. affine, rather than to one of the more abundant hipparionines
in the fauna (Cor. occidentale, Nannippus sp., cf. Nan. fricki, or
Hipparion tehonense), primarily on the basis of size (Tables 2 and
3), protocone shape, relatively simple fossettes, and pli caballin
development for uppers, and flattened labial protoconid and hypoconid
borders and size for the lowers (Fig. 3B). They were originally
referred by Forsten (1975) to Cor. occidentale, and some (but not
all) could represent extremes in that variable taxon. The differ-
ences in size among the three referred populations (Tables 2 and 3)
are exaggerated by small sample sizes and differing age-class
distributions. The recognition of Neo. affine in the Lapara Creek
Fauna is not surprising. It is a consistent, although typically rare
member of many similar age faunas in northern Texas, Nebraska and
South Dakota (MacFadden, 1984a). The latest appearance of Neo.
affine is late Clarendonian, in the Xmas-Kat faunal zone of Nebraska
(Skinner and Johnson, 1984). However, it has not yet been recorded
from Florida. As the time period during which it is most common is
still poorly known in Florida, this absence could well be the
artifact of a deficient record.
0 1 2cm
Figure 3. Occlusal views of cheekteeth of Neohipparion affine from
the Buckner Ranch Site, Bee County, Texas (early Clarendonian,
Lapara Creek Fauna). A. TMM 30896-395, L Ml, early to moderate
wear-stage. B. TMM 30896-574, L p3 or p4, early wear-stage.
Table 2. Standard univariate statistics for upper cheekteeth of
Neohipparion affine. Measurements defined in Chapter 3. The first
line for each entry gives i, s and n, the second line OR and V.
Populations are LC, Lapara Creek Fauna, Bee County, Texas; CLAR,
Clarendon Fauna, Donley County, Texas; and NEB, combined sample of
Clarendonian localities from Nebraska and South Dakota.
22.2, -- ,1
BAPL 17.5, -- ,
Table 3. Standard univariate statistics of lower cheekteeth of
Neohipparion affine. Measurements defined in Chapter 3. Format and
samples as in Taf e 2. No lower second premolars measured from
Lapara Creek sample.
19.4, -- ,1
22.4, -- ,
Neohipparion trampasense (Edwards), 1982
Neohipparion nr. N. eurystyle (Cope), HIRSCHFELD and WEBB, 1968,
Neohipparion cf. leptode Merriam, WEBB et al., 1981, p. 526;
HULBERT, 1982, pp. 159-160 (in part).
Hipparion trampasense EDWARDS, 1982, p. 174 (in part).
Neohipparion trampasense (Edwards), MACFADDEN, 1984a, p. 97.
Type specimen. UCMP 58234, a left upper molar.
Type localtiy. UCMP V6107, Bolinger Canyon, Contra Costa Co.,
California; Kendall-Mallory l.f.
Stratigraphic occurrence and age of type locality. Contra Costa
Group (undifferentiated), about 1300 feet above the top of the Neroly
Formation; late Clarendonian, about 10 ma.
Topotypic sample. As listed by Edwards (1982), except as
Distribution. Late Clarendonian of California; late Clarendonian
and early Hemphillian of Nebraska and Florida; early Hemphillian of
Referred specimens. J. Swayze Quarry, Clark Co., Kansas: F:AM
113734 L P2; 113735 R P2; 113736 R P34; 113737-113739 3 R M12; 113740
R p2; 113741 L p34; 113742-113743 2 R m12.
Xmas-Kat Fauna, Cherry Co., NB (see Skinner and Johnson, 1984, for
discussion of the geology and location of these quarries). Xmas
Quarry: F:AM 113756 P34; 114151 R mandible with p2-m3. Machaerodus
Quarry: F:AM 114152 assoc. R & L mandibles with dp2-dp4. Line Kat
Quarry: F:AM 71854 R mandible with p2-m3. Hans Johnson Quarry:
F:AM 114154 R mandible with dp2-dp4. East Kat Quarry: F:AM 113749 R
maxilla with P4-M3. Trailside Kat Quarry: F:AM 114155 L mandible
with dp2-dp4. Leptarctus Quarry: F:AM 113752, 113753 2 assoc. R & L
mandibles with p2-m3; 113754 assoc. R & L mandibles with p2-m2;
113751 L mandible with p2-p4; 113750 R P34; 113757 R M12.
Kepler Quarry No. 1 (UNSM loc. MO-101), Morrill Co., NB: UNSM
42449 (= AMNH 107595, cast) skull with R & L P2-M3 (MacFadden, 1984a,
McGehee Farm: UF 17211 R P34; 9607, 17132, 17134 3 R M12; 17129,
17133 2 L M12; 17135 R M3; 17136, 45594 2 L M3; 17159 assoc. R & L
mandibles with p2-m3; 45593 R mandible with p2-p3; 9500 assoc. R
ml-m3 & L p4-ml; 65177 L dp34; 45598 L p2; 17166, 17170, 45605 3 L
p34; 17141, 17143, 17171, 45601-45604, 53453 8 L m12; 17142, 17146,
19221 3 R m12; 9608, 9612, 45595, 45596 4 L m3; 17148, 17149, 19222,
45632 4 R m3.
Love Site: UF 32249 partial skull with R & L DP2-M1; 32291
partial skull with R & L DP2-M2; 25637 partial skull with R P4,M1,M3
& L P4-M3; 32248 assoc. maxillae with R DP2-DP4 & L DP2-M2; 32252
assoc. maxillae with R & L P2-M3; 32258 assoc. maxillae with R P3-M3
& L P2-M1,M3; 32251 R maxilla with M1-M3; 32272 L maxilla with P3-M2;
32253 L maxilla with P4-M3; 53427 L maxilla with P4-M1; 53428 L
maxilla with M2-M3; 32277 assoc. R DP2-DP4 & L DP2-DP3; 27991, 27992,
32256 3 assoc. R & L P2-M3; 32284 assoc. R P2-MI & L P2,M2-M3;
53204/53207 assoc. R P3-P4; 32273 assoc. L P3-M2 & R Ml; 32280 assoc.
L M1-M3; 32159 assoc. R & L mandibles with c,p2-m3; 27317 assoc.
mandibles with R il,i3,c,p4-m3 & L p2-m3; 32148/32153 assoc. mand-
ibles with R p2-m3 & L p3-m3; 32193 assoc. mandibles with R p4-m3 & L
ml-m3; 32192 assoc. mandibles with R p2-m3 & L p2-p4; 32121 R
mandible with dp2-dp4; 32145 L mandible with dp2-dp4,ml; 32213,
32216, 32218, 32162 4 R mandibles with p2-m3; 32110, 32216, 32152 3 L
mandibles with p2-m3; 32186 L mandible with p2-p3,ml-m3; 32179 R
mandible with p2-p3,dp4,ml-m2; 32175 R manidble with p3-m2; 32127,
32184 2 L mandibles with p2-m2; 32164, 32109, 32217 3 L mandibles
with p3-m3; 32168 L mandible with p2-p3,dp4,ml-m2; 32106, 32122,
32126, 32142, 32156, 32210, 32211, 32222, 32224, 32310, 32311, 36275,
36281, 36288 14 partial R mandibles; 32131, 32149, 32166, 32188,
32246, 35899, 36273, 36273, 36274 8 partial L mandibles; 32228,
32230, 32233, 32234, 32235, 32238, 32240, 35896, 36278, 68788-68791,
13 assoc. lower dentitions; over 850 individually catalogued isolated
Revised diagnosis. Medium-sized hipparionine with toothrow
lengths between 110 and 130 mm; DPOF very shallow depression set well
anterior to lacrimal. Unworn M12 MSCH about 60 mm; higher crowned
than Neo. affine, lower crowned than Neo. eurystyle, Neo. leptode or
Neo. gidleyi. Fossettes moderately complex; pli caballin strong,
often double on premolars; metastyle present but much weaker than in
Neo. eurystyle; pli caballinid persistently well developed on p2-p4
and dp2-dp4, on ml-m3 only in early wear-stages.
Description of Florida and Nebraska specimens. Other than
fragments, no cranial material was recovered with the topotypic
sample of Neo. trampasense (Edwards, 1982). The most complete
referable skull of Neo. trampasense is UNSM 42449 from the late
Clarendonian of Nebraska. It along with less complete cranial
material from the Love Site (UF 32251) demonstrate that Neo.
trampasense has a relatively small, very shallow DPOF developed only
on the maxillary and nasal bones, dorsal and posterior to the IOF.
It is located far anterior of the lacrimal, which is reduced in size
(Fig. 4). The malar region may have a slight depression (UF 32251,
Fig. 4), although this feature is absent in F:AM 113749 and UNSM
42449. The nasal notch is not deeply retracted, and lies over the
postcanine diastema. Mandibular and maxillary toothrow lengths in
moderate to early wear vary from 108 to 130 mm (ltrl of combined
sample from the Love Site and McGehee Farm, excluding heavily worn
individuals, has a R of 115.8 mm, s=4.42, n=7). Individuals from the
Great Plains average 5 to 10% larger. Lower diastema lengths range
from 53 to 59 mm for males (9=55.3 mm, s=2.48, n=5), while the only
measurable female had a ldl of 64.4 mm.
Upper cheekteeth of Neohipparion trampasense are generally
characterized by moderately complex fossettes, moderately elongated
protocones, deep hypoconal grooves, and well developed parastyles and
mesostyles. P2s in early wear-stages have well developed, pinched-
off anterostyles, slightly recurved parastyles, and small metastyles
(Fig. 5A). The P2 protocone is elongated, but shorter than that of
the P34, and typically connects to the protoselene during moderate
wear-stages. Complexity of fossette plications and pli caballin
development of the P2 rival or exceed slightly that of the P34.
0 1 2 3 4 5cm
Figure 4. Lateral view of right (reversed) facial region of
Neohipparion trampasense (UF 32251) from the Love Site, Alachua
County, Florida. LAC, lacrimal bone; DPOF, dorsal preorbita fossa.
Teeth in lateral view are the M1-M3.
0 1 2 3cm
0 1 2 3cm
Figure 5. Occlusal views of upper and lower cheekteeth of Neohipparion trampasense. A. UF 27991, L
P2-M3, early to moderate wear-stage, Love Site, Alachua County, Florida (very late Clarendonian). B.
UF 17159, L p2-m3, moderate wear-stage, McGehee Farm Site, Alachua County, Florida (early Hemphillian).
Figure 6. Occlusal views of upper cheekteeth of Neohipparion trampasense, all from the Love
Site, Alachua County, Florida (very late Clarendonian). A. UF32249, L P2-DP4, early wear-
stage. B. UF 36232, L P2, late moderate wear-stage. C. UF 53212, R P3 or P4, moderate wear-
stage. D. UF 53237, L M1, moderate wear-stage.
0 1 2cm
I I I
Table 4. Standard univariate statistics for upper cheekteeth of
Neohipparion trampasense. Format as in Table 2. Populations are LOV,
Love Site, Alachua County, Florida; KM, Kendall-Mallory l.f., Contra
Costa County, California (type locality); NEB, Xmas-Kat Quarries
Faunal Zone, Cherry County, Nebraska; and KAN, combined sample from
the J. Swayze Quarry, Clark County, Kansas and Arens Quarry, Norton
APL 24.9, 1.28, 50
24.8, -- ,1
26.4, -- ,1 27.7,2.11,4
18.6, -- ,1 19.1, -- ,1 20.6,1.10,4
7.1, - ,1
4.2, - ,1
6.3, - ,1
3.7, -- ,1
17.8, -- ,1 18.0,0.79,4
After moderate or heavy wear, the anterostyle becomes broadly
connected with the rest of the tooth, the protocone connection also
broadens, and the parastyle becomes less distinct (Fig. 6B).
Estimated unworn P2 MSCH is about 37-40 mm, based on a large sample
of slightly worn teeth (e.g. UF 36009, 36155, 36189). The P34 (Figs.
5A, 6C) are characterized by broad, well developed styles; elongated,
obliquely oriented (anterolabial-posterolingual) protocones isolated
until very near the base of the crown and rarely with spur; lingual
protocone borders generally concave; well developed, persistent,
often branched or double pli caballins; anterior half of prefossette
generally has a deep, unbranched pli protoloph, and one to three
labial accessory plications; the posterior half of the prefossette is
complexly plicated in early to moderate wear-stages, with a long,
secondarily plicated prefossette loop, and two to five plis
prefossette of varying depth and complexity; the anterior half of the
postfossette is strikingly less complex, with a deep, only rarely
branched pli postfossette, and one to three, most often one, small
accessory plications; and the posterior half of the postfossette
general has a single, deep, unbranched pli hypostyle. The hypoconal
groove is deep and broad in early wear-stages, shallower with wear
but open to the base of the crown. The DP2-DP4 (Fig. 6A) are more
complex than their permanent counterparts, typically with multiple or
branched pli caballins; intricately plicated fossettes in early wear;
and more oval protocones with flat or convex lingual borders. The
DPI is very rudimentary and lost prior to the replacement of the DP2
by the P2 (e.g. UF 32291). Estimated unworn P34 MSCH is about 52 to
The upper molars are distinctly smaller than the premolars (Table
4; Figs. 5A, 6D); with elongate-oval, isolated protocones not so
obliquely orientated; and less pronounced styles. The lingual
borders of molar protocones are generally flat or convex, only
occasionally concave. Pli caballins are generally single, and-
smaller than in the premolars. The anterior half of the prefossette
most often has a moderately deep, unbranched pli protoloph without
accessory plications. The posterior half of the prefossette has a
long prefossette loop and one to four shallow plis prefossette. The
anterior half of the postfossette has a deep, sometimes branched pli
postfossette and up to four accessory plications. The posterior half
of the postfossette generally has a single, unbranched pli hypostyle.
About 32% of all observed molars in early and early-to-moderate wear-
stages (MSCH > 35 mm; n=93) resemble the holotype, UCMP 58234, in
having one or two accessory plications in addition the pli protoloph.
Estimated unworn M12 MSCH about 57 to 60 mm. The hypsodonty index of
the Love Site population is 3.9.
The Love Site sample of associated and isolated lower teeth is
large enough to provide numerous examples of every wear-stage (Table
5; Figs. 5B, 7). Deciduous lower premolars have very elongated
metaflexids and entoflexids; well developed pli caballinids; shallow
ectoflexids; very small or absent ectostylids (the tooth is shed
before they are exposed to wear); and less frequent isthmus
plications than on the permanent premolars (Fig. 7E). The dpi is
Figure 7. Occlusal views of lower cheekteeth of Neohipparion trampasense, all from the Love
Site, Alachua County, Florida (very late Clarendonian). A. UF 32237, R p3-m2, moderate wear-
stage. B. UF 50537, R p3 or p4, early wear-stage. C. UF 50587, L ml, early wear-stage. D. UF
64720, L ml or m2, late wear-stage. E. UF 32240, R dp2-dp3, moderate wear-stage.
0 1 2cm
I I I
Table 5. Standard univariate statistics of lower cheekteeth of
Neohipparion trampasense. Format as in Table 2, sample populations as
in Table 4.
21.9, -- ,1 23.1,1.17,5
8.5, -- ,1 8.3,0.47,5
9.8, -- ,1 10.0,0.78,5
8.7, -- ,1 9.9,0.61,5
9.5, -- ,1 10.8,0.76,5
19.4, -- ,1
16.2, -- ,1
small, rudimentary, and shed with the eruption of the p2. Lower
permanent premolars (Figs. 5B, 7A, 7B) are characterized by shallow
ectoflexids that do not penetrate the isthmus even in late wear-
stages; persistent pli caballinids; well developed protostylids;
plicated isthmuses and paralophids; expanded, subequal metaconids and
metastylids well separated throughout all wear-stages; linguaflexid
very broad, shallow, "U"-shaped in early wear occasionallyy with a
lingual plication), with wear, narrower and more "V"-shaped; labial
borders flat in early wear, with heavy wear they may take on a more
rounded appearance. Lower molar morphology changes even more
dramatically with wear. In very early wear-stages the ml and m2 are
very long, with many features similar to those observed in the
premolars, such as shallow ectoflexids and well developed pli
caballinids (Fig. 7C). Following the eruption of the m3, the m12 APL
becomes shorter; ectoflexids deepen with gradual penetration of the
entire isthmus (Figs. 5B, 7A); pli caballinids fade, although in
moderate wear-stages their appearance is somewhat variable;
metaflexids and entoflexids shorten; and the labial borders of the
protoconid and hypoconid become rounder. In late wear-stages (Fig.
7D), molars lack or have only rudimentary pli caballinids; have deep,
"V"-shaped linguaflexids and ectoflexids; and have oval metasylids
and metaconids. Unworn mcch about 36 to 37 mm for p2, 48 to 51 mm
for p34, and 58 to 60 mm for m12.
Discussion. As noted by MacFadden (1984a), Neo. trampasense is
clearly a member of Neohipparion based on its cranial, facial and
dental features. For many characters, Neo. trampasense is
intermediate between those found in basal hipparionine stock or Neo.
affine, and those in the Neo. eurystyle species-group. The topotypic
Bolinger Canyon sample of Neo. trampasense is the oldest population
referred to the species (about 10 ma, Edwards, 1982), and the least
progressive as well. When compared with the Nebraska and Florida
samples, its protocones are more oval and have flat lingual borders
(rarely concave); the lower premolars tend to lose the pli
caballinids with heavy wear (e.g. UCMP 77031); and the molars have
only rudimentary pli caballinids in moderate wear-stages (e.g. UCMP
58244). However, in many features, such as size (Tables 4, 5),
hypsodonty, fossette complexity, metastyle development, reduction of
ectoflexid depth in premolars, and flattened labial borders of lower
premolars, the Bolinger Canyon sample so closely approaches or equals
that seen in later Clarendonian and early Hemphillian samples that
they are considered the same species.
Several specimens referred by Edwards (1982) to Neo. trampasense
from the type locality clearly do not belong with that species as it
is now defined. These include UCMP 77032 (L P3-M1), UCMP 58223 (L
M1-M2, not P4-MI as stated by Edwards, 1982, p. 174), UCMP 58225 (L
P34), UCMP 112771 (L p34) and UCMP 112154 (R & L dp2-dp4). The upper
cheekteeth of these specimens are characterized by short, oval proto-
cones with well developed spurs and convex lingual borders. In
protocone morphology, as well as size, fossette complexity, and
stylar development they match the topotypic sample of Hipparion
force (Richey, 1948; e.g. UCMP 94815, a L Ml). The associated lower
dentition is also probably referable to H. force because of its lack
of pli caballinids, moderately developed ectostylids, rounded labial
borders, and relatively short metaflexids and entoflexids. UCMP
112154 does not differ significantly from the large sample of decid-
uous lower premolars of H. force from Black Hawk Ranch. Perhaps the
inclusion of these Hipparion teeth in his sample contributed to
Edwards placing his new species in Hipparion rather than Neohip-
parion. Finally, Edwards (1982) listed UCMP 58239 as both a L p4-ml
(p. 174) and a L m2-m3 (p. 182). The specimen is clearly a L p3-p4
(of Neo. trampasense), as the more anterior tooth is undoubtedly a
premolar, and thus the very slightly worn posterior tooth cannot be a
molar (as the ml erupts well prior to the p4 in all equids).
MacFadden (1984a) only referred one specimen from the Xmas-Kat
Fauna of Nebraska to Neo. trampasense. Examination of previously
uncatalogued material in the F:AM collection revealed a number of
specimens referable to this species from this fauna, and from other
sites in Nebraska and Kansas. Neo. trampasense is thus more common
in the Great Plains than previously thought, and apparently is a
useful biochronological indicator of the late Clarendonian and early
Hemphillian across North America.
A number of derived dental character states found in Neo.
trampasense, some only in early wear-stages, indicate a close
relationship with later Hemphillian species of Neohipparion. In the
upper dentition these include the flattened protocones, often with
concave lingual borders, and the well developed styles. Small
metastyles are much more frequent than in Neo. affine. However, it
is in the lower cheekteeth that Neo. trampasense best shows its
advanced features. In the premolars, the ectoflexids do not
penetrate the isthmus, even with heavy wear, nor is there reduction
of the pli caballinids. The labial borders tend to be very flat, and
the metaconids and metastylids are long and well separated. In
molars, pli caballinids are consistently found in early wear-stages,
and there is some reduction of the depth of the ectoflexids.
However, in late wear, the molars take on the primitive hipparionine
morphology (Fig. 7D). The lower dental morphology in the sequence
Neo. affine - Neo. trampasense - Neo. eurystyle details the evolution
of a caballoid dental pattern (sensu Forsten, 1982; 1984) from the
primitive hipparionid pattern. This pattern evolved independently
several times to varying degrees in equid lineages during the Late
Neogene. In some respects, that attained by Neohipparion was the
most advanced in the Equidae (Rensberger et al., 1984). The chrono-
logical sequence of Neo. trampasense populations demonstrates a pos-
sible mechanism (heterochrony) of how this ultimate pattern evolved.
Younger populations (early Hemphillian) of Neo. trampasense tend
to retain advanced characters such as reduced depth of the ectoflexid
and pli caballinid development in molars through later wear-stages
than do older populations (late Clarendonian). Referred specimens of
Neo. trampasense from early Hemphillian localities in Kansas (J.
Swayze and Arens Quarries) also have significantly larger tooth
dimensions (Tables 4, 5); these combined suggest an evolutionary
trend that resulted in the western species Neo. leptode. The rela-
tively early (and most primitive) appearance of Neo. eurystyle is in
Florida (see below) from Moss Acres and With 4A. This suggests that
Neo. eurystyle evolved from eastern populations of Neo. trampasense,
perhaps in the Gulf Coastal Plain.
Neohipparion eurystyle (Cope), 1893
Equus eurystylus COPE, 1893, pp. 43-45.
Hipparion eurystylus (Cope), GIDLEY, 1901, p. 125.
?Hipparion eurystylus (Cope), GIDLEY, 1907, p. 918.
Neohipparion eurystyle (Cope), MERRIAM, 1915, p. 4; STIRTON,
1940; p. 183; MACFADDEN, 1984a, p. 105 (in part).
Hipparion eurystyle (Cope), OSBORN, 1918.
Hipparion phosphorum SIMPSON, 1930, p. 189.
Hipparion (Neohipparion) eurystyle (Cope), MATTHEW and STIRTON,
1930, p. 362.
Neohipparion floresi STIRTON, 1955, p. 886.
Neohipparion arellanoi STIRTON, 1955, p. 888.
Neohipparion otomii MOOSER, 1960, p. 376; DALQUEST and MOOSER,
1980, p. 11.
Neohipparion monias MOOSER, 1964, p. 394; DALQUEST and MOOSER,
1980, p. 12.
Neohipparion cf. phosphorum (Simpson), WEBB and TESSMAN, 1968,
Hesperohipparion stirtoni DALQUEST, 1981, p. 510.
Type specimen. TMM 40289-1, a partial left lower molar.
Type locality. Palo Duro Canyon, Randall Co., Texas. Possibly
the Currie Ranch Site (Schultz, 1977; Dalquest, 1981).
Stratigraphic occurrence and age of type locality. Ogallala
Group; late Hemphillian, about 5 ma.
Distribution. Early late to latest Hemphillian of Mexico, Texas,
Oklahoma, Kansas and Nebraska. Late early through latest Hemphillian
of Florida. Possibly California.
Referred Florida specimens. Moss Acres Racetrack Site: UF 95410
assoc. R M2 & L M2-M3; 65250 R mandible with dp3-ml; 69969 R mandible
with p2-m3 and R il-i3 & L il.
With 4A: UF 45518 R P2; 45520 R M3; 45546 R pd2; 17306 R p2.
With 4X: UF 53524 R P34.
Mutual Mine, near Dunnellon, Marion Co., FL: UF/FGS V-7175 L M12;
-7176 R P34; -7179 R p34; -7180 L p34; -7178 R m12; -7177 R m3.
Manatee Dam Site: UF 11940 R P2.
Lockwood Meadows: UF 64116 R P34.
Palmetto Fauna, Bone Valley Region. Palmetto Mine: UF 17154
assoc. R ml-m3; 17114 L P2; 17115, 53529, 53534-53537, 53541 7 R P34;
53530, 53540 2 R M12; 17116, 17118, 53531, 53538 4 L M12; 53532 R M3;
17119, 53542, 53543 3 L M3; 17162 R dp3; 53479 L p2; 53509, 53496, 2
R p34; 17157 R m12; 12501, 53500 2 L m12; 12061, 53499 2 R m3; 17158
L m3. North Palmetto Mine: UF 18725 L M3; 18728 L m3. Payne Creek
Mine: UF 18318 assoc. R & L P4-M3; AMNH 113755 L p34. Chicora Mine:
UF 17155 R m12. Fort Green Mine: UF 53902, 53903, 57342, 58309 4 R
M12; 24657 L M3; 53506 R m12. Nichols Mine: UF 24629 L P34. Agrico
Mine: UF/FGS V-5505 R P34; -1423 L M12 holotypee Neo. phosphorum);
-5473 L m3; AMNH 95627 R m12. Silver City Mine: UF 65698 R M3.
Kingsford Mine: UF 17120 L P2; 53544 L M12; 17151 L p2; 53559 R m12;