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Group Title: Bulletin of the Florida State Museum
Title: Postcranial osteology of the waterfowl
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
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Permanent Link: http://ufdc.ufl.edu/UF00001502/00001
 Material Information
Title: Postcranial osteology of the waterfowl
Series Title: Bulletin of the Florida State Museum
Physical Description: 129 p. : illus. ; 23 cm.
Language: English
Creator: Woolfenden, Glen Everett, 1930-
Publisher: University of Florida
Place of Publication: Gainesville
Publication Date: 1961
 Subjects
Subject: Water birds   ( lcsh )
Skeleton   ( lcsh )
Birds -- Anatomy   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Based on thesis, University of Florida.
Bibliography: "Literature cited:" p. 126-129.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00001502
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA0810
notis - ACK0665
alephbibnum - 000440284
oclc - 03366255
lccn - a 62009717

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Full Text




BULLET


OF THE


FLORIDA STATE

BIOLOGICAL SC


Volume 6


MUSEUM


IENCES


Number I


POSTCRANIAL OSTEOLOGY


OF THE WATERFOWL


Glen E. Woolfenden


UNIVERSITY OF FLORIDA
Gainesville
1961


IN








Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM are pub-
lished at irregular intervals. Volumes contain about 300 pages and are not
necessarily completed in any one calendar year.


















WILLIAM J. RIEMER, Managing Editor

OLIVER L. AUSTIN, JR., Editor




Consultants for this issue:

Hildegarde Howard
Jean Delacour




















Communications concerning purchase or exchange of the publication and all
manuscripts should be addressed to the Managing Editor of the Bulletin, Florida
State Museum, Seagle Building, Gainesville, Florida.


Price for this issue $1.60


Published 28 June 1961j










POSTCRANIAL OSTEOLOGY OF THE WATERFOWL

GLEN E. WOOLFENDEN1

SYNOPSIS: Postcranial osteology of nearly all the genera of waterfowl of the
world is described. On the basis of this study certain changes in the classifica-
tion within the order are proposed. In comparison with the most recent classifi-
cation of the waterfowl, that of Delacour, the following changes are proposed:
Anseranas is placed in a monotypic family; Stictonetta is removed from the
Anatini and placed tentatively in the Dendrocygnini of the Anserinae; Cereopsis
is moved from the Tadornini to a monotypic tribe of the Anserinae; Plectropterus
is moved from the Cairinini to the Tadornini; Tachyeres is moved from the
Tadornini to the Anatini; the tribe Cairinini is merged with the Anatini; Mer-
ganetta is moved from the Anatini to a monotypic tribe; Rhodonessa is moved
from the Anatini to the Aythyini; the tribe Somateriini is merged with the Mergini.
The following genera are resurrected: Olor, Nesochen, Callonetta, Pteronetta,
Metopiana, Mergellus, Lophodytes, and Nomonyx, and, tentatively, Asarcornis
and Salvadorina.


TABLE OF CONTENTS
Page
Introduction ---------------- 2
Acknowledgments ------------------ 2
Materials and methods ---------------------------------. 3
Descriptive osteology -- ----------- 5
Humerus ..------------------------------------ 6
Carpometacarpus -------------- 21
Sternum ------------ ------------------------- 34
Coracoid ------------------------------------- 46
Scapula --------------------------------- 59
Furculum ---------------------------------------------------------------------------------------------------------- 64
Femur __. ..-------------- 66
Tibiotarsus ------ --------------------------- 73
Tarsometatarsus -- --------------------------------- 79
Pelvis -------------------------------------------- 86
Vertebral column ----------- --- ------------------ 89
Discussion and conclusions-------------- 9E
Appendix: Ligaments of the pectoral girdle ----- 124
Literature cited ------------------------------------ 126


The author, Instructor in Biological Sciences at the University of South Florida,
Tampa, completed this work while a graduate student and an instructor at the
University of Florida, Gainesville. An earlier version formed his doctoral disserta-
tion and was accepted by the Graduate School in August 1960. Manuscript sub-
mitted 19 December 1960.-ED.






BULLETIN FLORIDA STATE MUSEUM


INTRODUCTION
It seems logical that the waterfowl, as the Anatidae are commonly
known, should be a well-studied group. They have great economic and
recreational value, and many species are easily reared in captivity. No
living species completely new to science has been discovered since
1894. But, as Delacour and Mayr (1945) point out, their internal anat-
omy is a completely neglected field. Until Verheyen's osteological
work (1955), no modern comparative anatomical study of all the taxa
within the family was ever undertaken.
Verheyen bases his classification almost entirely on the number of
vertebrae in the different regions of the column and on relative lengths
of various limb elements. He admits that structural details of the in-
dividual bones are of great importance to paleontologists, but further
states, somewhat antithetically, that such features rarely serve to dis-
tinguish one waterfowl from another. Previous work with anatid fos-
sil material convinced me that a detailed analysis of the structure of
their bones might contribute significantly to better understanding of
waterfowl phylogeny.
Many osteological studies emphasize the relative lengths of limb
bones. This characteristic may be of significance between closely re-
lated species, but in such ancient and diverse groups as the waterfowl,
it seems likely that relatively similar proportions could have arisen in-
dependently several times. The concept that structural features of the
different elements may be more significant than relative sizes underlies
this study.
As the skull is treated by other investigators (Verheyen, 1955; Good-
man and Fisher, MS), the present study is based primarily on quali-
tative structural differences in 10 postcranial elements. The relative
taxonomic usefulness of these elements is respectively: humerus, car-
pometacarpus, coracoid, sternum, tarsometatarsus, femur, tibiotarsus,
scapula, pelvis, and furculum. Size and other characters of a specific
nature variable within the genus are disregarded. The ulna, radius,
and fibula are generally considered of lesser taxonomic value and were
not studied.
Anatomical nomenclature follows Howard (1929). In a few in-
stances it has been necessary to name other features. When an addi-
tional term is first used, it is defined or a reference is cited.

ACKNOWLEDGMENTS

I extend my deep appreciation to Professor Pierce Brodkorb for his
valuable and untiring supervision throughout the course of the problem.


Vol. 6







WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Sincere thanks are also due to the other biologists who critically read
the manuscript, Oliver L. Austin, Jr., Jean Delacour, J. C. Dickinson,
Jr., Hildegarde Howard, Roland F. Hussey, and James N. Layne. To
Ted T. Allen, who made the drawings, and Robert W. McFarlane and
J. Hill Hamon, who did the photographic work, I am also grateful.
Finally, I wish to acknowledge financial aid from a grant from the Sig-
ma Xi-RESA Research Fund and also from Lester B. Woolfenden and
Gwen S. Woolfenden.

MATERIALS AND METHODS
The skeletal collection of Pierce Brodkorb was supplemented by ma-
terial borrowed from the American Museum of Natural History, United
States National Museum, National Museum of Victoria, Australia, and
Peabody Museum of Natural History; these specimens were obtained
through the kindness of Dean Amadon, Herbert Friedmann, A. R.
McEvey, and Philip S. Humphrey, respectively. Additional material
was donated by Richard G. Naegeli, Director of Busch Gardens, Ethel
L. Woolfenden, Joseph R. Jehl, Jr., Charles T. Collins, William O.
Wirtz II, and Henry M. Stevenson, Jr. Norman L. Ford sent data from
specimens in the University of Michigan Museum of Zoology.
Over 85 percent of the currently recognized genera were studied.
Only 8 of the 62 genera recognized by Peters (1931) were unavailable,
namely Cyanochen, Asarcornis, Stictonetta, Pseudotadorna, Nesonetta,
Salvadorina, Camptorhynchus, and Thalassornis. By Delacour's classi-
fication (1954, 1956, 1959) only 5 of his 41 genera were lacking, namely:
Cyanochen, Stictonetta, Lophonetta, Camptorhynchus, and Thalas-
sornis.
The assembled collection of 432 specimens represents 105 of the
167 species of waterfowl recognized by Peters. Those species and sub-
species examined and the number of specimens involved are:

Cygnus cygnus 2 Anser anser 1
C. columbianus 24 A. albifrons albifrons 1
C. buccinator 1 A. fabilis 1
C. olor 2 Eulabeia indica 1
C. melancoriphus 3 Cygnopsis cygnoid 2
Chenopis atrata 4 Philacte canagica 1
Anseranas semipalmata 1 complete + Branta bernicla hrota 6
1 body skeleton B. b. nigricans 1
Plectropterus gambensis 2 B. canadensis canadensis 8
Cereopsis n.hollandiae 2 B. c. hutchinsii 2
Chen caerulescens 1 B. ruficollis 1
C. hyperborea 2 Nesochen sandvicensis 1
C. rossii 9 Chlophaga melanoptera 4






BULLETIN FLORIDA STATE MUSEUM


C. leucoptera 1
C. dispar 3
Chenonetta jubata 2
Dendrocygna viduata 1 complete + 1
body skeleton
D. bicolor bicolor 1
D. javanica 2
D. autumnalis autumnalis 1
D. a. discolor 1 body skeleton
D. arborea 3
Alopochen aegyptiaca 3
Neochen jubata 1 complete + 1 body
skeleton
Sarkidiornis melanota 1
Cairina moschata 4
Coscoroba coscoroba 1
Casarca cana 2
C. tadornoides 1
C. variegata 2
Tadorna tadorna 4
Anas platyrhynchos platyrhynchos 6
A. poecilorhyncha 1
A. luzonica 1
A. melleri 1
A. fulvigula fulvigula 7
A. f. maculosa 1
A. rubripes 6
A. undulata 1
A. cyanoptera cyanoptera 3
A. discors 10
A. querquedula 4
A. castanea 2
A. crecca crecca 1
A. c. carolinensis 10
A. formosa 1
A. falcata 1
A. leucophrys 1
A. brasiliensis 1
A. acuta tzitzihoa 5
A. angustirostris 1 body skeleton
A. bahamensis rubirostris 2
Mareca penelope 14
M. americana 4
M. sibilatrix 1
Chaulelasmus streperus 9
Spatula clypeata 5
S. platalea 1
Malacrohynchus membranaceus 1 com-
plete + 1 partial skeleton


Rhodonessa caryophyllacea 1 body
skeleton
Aix sponsa 16
Dendronessa galericulata 5
Cheniscus coromandelianus coromandel-
ianus 4
C. pulchellus 1
Nettapus auritus 1
Pteronetta hartlaubii 1
Heteronetta atricapilla 1
Netta rufina 2
Metopiana peposaca 3
Aythya ("Nyroca") valisineria 3
A. ferina 1
A. americana 5
A. collaris 14
A. fuligula 6
A. nyroca 1
A. marila marila 21
A. m. nearctica 6
A. affinis 25
Tachyeres brachyptera (i.e., pteneres) 1
Bucephala clangula clangula 2
B. c. americana 5
B. albeola 7
Clangula hyemalis 5
Histrionicus histrionicus pacificus 1
Somateria mollissima v-nigra 1
S. m. dresseri 7
S. spectabilis 3
Arctonetta fisher 1
Oidemia nigra nigra 3
0. n. americana 1
Melanitta fusca fusca 1
M. f. deglandi 5
M. perspicillata 1
Polysticta stelleri 1
Hymenolaimus malacorhynchos 1
Nomonyx dominicus 2
Oxyura jamaicensis jamaicensis 11
0. vittata 1
Biziura lobata 1
Mergellus albellus 1
Lophodytes cucullatus 7
Mergus merganser merganser 2
M. m. americanus 2
M. serrator 18
Merganetta armata armata 2


Vol. 6







WOOLFENDEN: OSTEOLOGY OF WATERFOWL


All the ratios presented are intramembral and reflect relative pro-
portions within a given element. Obtained by dividing the width or
depth of various portions of the element by its length, the ratios are
expressed as percent of the length. Linear measurements are taken to
the nearest tenth of a millimeter. The methods of taking the measure-
ments are explained where first mentioned under each element.

DESCRIPTIVE OSTEOLOGY

Listed below are the genera of Anatidae according to Peters (1931), ar-
ranged in the subfamilies and tribes of Delacour (1954, 1956, 1959).
Two generic changes (Aythya for Nyroca, cf. American Orinthologists'
Union, 1945; Lampronetta for Arctonetta, cf. Parkes, 1955), and two
additions (Lophonetta and Amazonetta from Anas, cf. Delacour and
Mayr, 1945) are incorporated. Parentheses enclose the genera not rec-
ognized by Delacour, and these follow the genera with which they are
synonymized. Asterisks mark the genera not available for this study.
Where additional genera are mentioned in the text an authority is
listed. I have altered slightly the vernacular names of certain of the
tribes and the arrangement of the tribes in the subfamily Anatinae.
The latter change allows for clearer presentation of the osteological
data which follow this arrangement:

Subfamily Anseranatinae (Pied Goose) Anseranas.
Subfamily Anserinae (Whistling Ducks, Swans and Geese).
Tribe Dendrocygnini (Whistling Ducks) Dendrocygna.
Tribe Anserini (Swans and Geese) Coscoroba; Cygnus, (Chenopis); Anser,
(Cygnopsis), (Chen), (Philacte), (Eulabeia); Branta, (Nesochen).
Subfamily Anatinae (Ducks).
Tribe Tadornini (Sheldrakes) Cereopsis; Chloiphaga; Cyanochen*; Neochen;
Alopochen; Tadorna, (Casarca), (Pseudotadorna)*; Lophonetta*; Tachyeres.
Tribe Anatini (Dabbling Ducks) Anas, (Nesonetta)*, (Chaulelasmus), (Mareca),
(Spatula), (Salvadorina)*; Rhodonessa; Malacorhynchus; Hymenolaimus; Mer-
ganetta; Stictonetta*.
Tribe Cairinini (Perching Ducks) Amazonetta; Chenonetta; Aix, (Dendronessa);
Nettapus, (Cheniscus); Sarkidiornis; Cairina, (Asarcornis)*, (Pteronetta);
Plectropterus.
Tribe Aythyini (Pochards) Netta, (Metopiana); Aythya.
Tribe Somateriini (Eiders) Polysticta; Somateria, (Lampronetta).
Tribe Mergini (Sea Ducks) Melanitta, (Oidemia); Camptorhynchus*; Histrionicus;
Clangula; Bucephala; Mergus, (Mergellus), (Lophodytes).
Tribe Oxyurini (Stiff-tailed Ducks) Oxyura, (Nomonyx); Thalassornis*; Biziura;
Heteronetta.


1961







BULLETIN FLORIDA STATE MUSEUM


Humerus
Paleontologists and osteologists generally consider the humerus in birds
to be extremely useful taxonomically. Of the 10 elements described
herein, it shows the greatest number of characters of systematic value.
ANSERANATINAE
The pied goose (Anseranas semipalmata) differs from all other Anatidae
by three humeral characteristics: (1) The prominent capital shaft ridge
(Ashley, 1941) is situated more medially. Correspondingly, the at-
tachment of the external head of the triceps is restricted; it barely ex-
tends proximally to the base of the internal tuberosity. In all other
waterfowl it extends past the tuberosity toward the head of the hum-
erus. (2) The pneumatic fossa is greatly reduced. The fossa does not
extend to the humeral head, and the floor is elevated from the bicipital
surface. (3) The facet for the anterior articular ligament is less elevat-
ed, particularly along the inner margin.
Because of its superficial resemblance to Plectropterus, Delacour
and Mayr (1945) treated Anseranas as an aberrant member of the perch-
ing ducks. Further consideration led Delacour (1954) to place Anser-
anas in a separate subfamily on anatomical evidence presented by
Boetticher (1943), who considers several skeletal features important.
The structure of its humerus shows Anseranas to be a primitive anatid,
and completely justifies its removal from the Anatinae.

ANSERINAE
Delacour and Mayr place the whistling ducks and swans and geese in
the same subfamily. Similarity in the form of the humeral head in
Dendrocygna and certain geese has been noted previously (Wetmore,
1924). The prominent capital shaft ridge directed towards the humeral
head, coupled with an area of attachment for the external head of the
triceps that extends virtually to the humeral head, characterizes the
subfamily. In the Anserinae and Anseranatinae the area of pectoral at-
tachment on the external tuberosity is elevated and somewhat circular;
in the Anatinae it lies essentially flush with the proximal portion of the
shaft and is elongate. In the Anserinae and the Anseranatinae the cap-
ital groove is not extensive, whereas in the Anatinae it extends laterally
over the anconal surface and undercuts the head considerably.
TRIBE DENDROCYGNINI (WHISTLING DUCKS). The humerus of whistling
ducks can be distinguished from those of the swans and geese, and also
of Anseranas, by the width of the space between the external condyle
and the facet for the anterior articular ligament in relation to the facet's


Vol. 6
























1


FIGURE 1. Right humerus, anconal view. Top row: Anseranas semipalmata,
Dendrocygna autumnalis, Cygnus melancoriphus, Branta bernicla, Cereopsis n.
hollandiae. Bottom row: Chlodphaga melanoptera, Anas platyrhynchos, Merga-
netta armata, Aythya maria, Clangula hyemalis, Oxyura jamaicensis.


'U

f~1


WOOLFENDEN: OSTEOLOGY OF WATERFOWL


IN






8 BULLETIN FLORIDA STATE MUSEUM Vol. 6

width. In the whistling ducks the space is narrower than the facet,
whereas in the swans and geese the reverse is true .
The small size of the humerus and its prominent capital shaft ridge
have been considered distinctive of Dendrocygna. These two features
alone, however, do not separate the genus from the smaller true geese.
TRIBE ANSERINI (SWANS AND GEESE). The prominent capital shaft ridge,
the extension of the area of attachment for the external head of the tri-
ceps almost to the humeral head, and narrowness of the facet for the
attachment of the anterior articular ligament (narrower than the space
between the facet and the external condyle) define this tribe.
Features of the humerus indicate the tribe is comprised of two dis-
tinct units, one containing the swans and Coscoroba, the other the
geese. These two units are distinguishable by the relative width of the
distal end of the humerus. In the swans the relatively narrow distal
end constitutes 12.2 to 13.9 percent of the total length, and in Coscoroba
13.9 percent. In geese the range is from 14.1 to 15.6 percent.
Further characteristics distinguishing these two groups pertain to
the configuration of the internal tuberosity and entepicondyle. (1)
The entepicondyle is not extended distally as far in swans as in geese.
(2) The entepicondylar prominence is more produced laterally in swans,
in part the result of the more medially-situated entepicondyle. (3) The
internal tuberosity is shorter and more rounded at the tip in swans.
In true swans a short, wide furrow leads transversely from near the
proximal end of the capital groove onto the internal tuberosity; this
furrow is indistinct in Coscoroba.
Neither Peters nor Delacour recognize the genus Olor as distinct
from Cygnus. Other authorities (Wetmore, 1951) consider the separa-
tion of the swans into two or more genera warranted. Howard (1946)
lists several distinguishing features of the humerus. (1) The inter-
muscular line on the capital shaft ridge is short, indefinite, and not turn-
ed inward below the head in Cygnus. In Olor the line runs along the
ridge and turns inward about 1/4 inch below the head. (2) The area of
attachment of the supraspinatus is clear-cut in outline and situated be-
low the pneumatic foramen; it is bordered by a raised line continuous
with the median crest in Cygnus (poorly marked in C. melancoriphus).
In Olor the attachment is less clearly marked and spreads past the
median crest, and it lacks the raised bordering line at the edge. (3)
The ligamental furrow is broad and shallow in Cygnus olor, but not in
C. melancoriphus, whereas in Olor it is narrower and deeper. (4) The
attachment of the anterior articular ligament is short, broad, and heav-
ily bordered on its outer edge next to the attachment of the pronator






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


brevis in Cygnus. In Olor the attachment is long, narrow, and smooth-
ly rounded at the edges. (5) The impression of the brachialis anticus
in Olor is short, broad (particularly at the proximoexternal edge) clearly
outlined, and usually deeply depressed. In Cygnus the impression is
less clearly outlined. The series of swans available to me confirm these
features, the last of which proves particularly useful. Chenopis is sim-
ilar to Cygnus in all these features.
The humeri of the true geese, Branta, Nesochen, Anser, Cygnopsis,
Eulabeia, Philacte, and Chen are very similar. Two specimens of Cyg-
nopsis, both aviary birds, are distinguishable from the other genera
through the larger, more rounded and distally extended pneumatic
fossa which excavates more of the shaft and the bone forming the me-
dian rim of the fossa.
Miller (1937) was unable to distinguish the humeri of Philacte,
Anser, and Chen from one another, but found the impression of the
external head of the triceps somewhat useful in separating Nesochen
and Branta from these three genera. The impression has a distinct
border in Nesochen and Branta, whereas in Philacte, Anser, and Chen
it is most often indistinct. Cygnopsis and Eulabeia resemble the latter
group in this respect. Miller remarks that Branta shows greater curv-
ature distally; with my series this feature is not particularly useful.
Brodkorb (MS) mentions that the deltoid crest in anconal view shows
a distinct bend in the middle in Branta, whereas in Philacte, Anser and
Chen it is more rounded. In a now larger series of geese we find this
feature useful in most cases, but not infallible. Nesochen and Eulabeia
resemble Branta in this character.
One feature of the humerus, although not infallible, aids in separ-
ating Chen from Anser and Philacte. In Chen the humerus, in anconal
view, has the head rotated toward the internal side, and thus the lip
of bone extending from the head over the capital groove is more prom-
inent. As only two specimens of Anser are available it is difficult to
assess the value of this character.

ANATINAE
Duck humeri lack the prominent capital shaft ridge directed toward
the head that is typical of the Anserinae (Cereopsis is an exception, see
Tadornini, paragraph 7). A few ducks have a humeral ridge directed
toward the external tuberosity, but most lack it. In Anatinae the capi-
tal groove extends laterally over the anconal surface and deeply under-
cuts the head. The differences in size and position of the capital shaft
ridge seem to result from a difference in the attachment of the external
head of the triceps, which is stronger in the Anatinae. Miller (1937)







BULLETIN FLORIDA STATE MUSEUM


postulates that greater strength of the muscle is indicated by the more
lateral position of the ridge in Chloephaga (here placed in the Anatinae)
as compared with certain true geese.
The structure of the humerus of the Anatinae indicates that the
sheldrakes and stiff-tailed ducks are the two most distinct tribes; where-
as the dabbling ducks, perching ducks, pochards, eiders, and sea ducks
are more closely related to one another.
TRIBE TADORNINI (SHELDRAKES). The sheldrakes have the following
humeral characteristics: (1) The capital shaft ridge is fairly prominent
as in Anserinae, but is directed towards the external tuberosity. (2)
The area of origin of the external head of the triceps is narrower than
in other ducks; as a result the area between the attachment of the
muscle and the external tuberosity is elevated. (3) The deltoid crest
is larger and more flaring than in other ducks. Furthermore, when
compared in lateral view, the entire crest tends to be more rounded, and
when an abrupt bend is present it lies more posteriad. (4) The deltoid
crest extends farther distally (most evident when the distal borders of
deltoid and bicipital crests are compared). (5) The head is rotated so
that the external tuberosity is usually higher or more anconal in rela-
tion to the head than in other ducks. This feature is best seen by view-
ing the proximal end of the bone with the palmar surface lying on a
horizontal plane. The external tuberosity represents more than 89
percent of the height of the head in the sheldrakes, with Tachyeres and
Neochen as exceptions. (The height of the humeral head is the distance
between the plane on which the palmar surface lies and a parallel
plane touching the anconal surface of the head). In Neochen the head
is rotated as in other members of the tribe, but a robust head results
in the external tuberosity constituting only 87.2 percent of the head
height. Tachyeres measured 86.2 percent and showed no indication of
the rotation present in the other genera assigned to this tribe.
Miller (1937) remarks on the striking modification of Chlophaga,
namely the much broader depression of the triceps, which is directly
related to the more lateral position of the capital shaft ridge and the
external flaring of the deltoid crest. A feature he does not mention
that further distinguishes Chloephaga from the true geese and relates
it to the other sheldrakes is the greater elevation of the facet for the
anterior articular ligament. Miller (1937) felt that Chloephaga would
prove to be more closely related to some anserine other than the North
American geese. The relationship appears even more distant than he
suspected, and more recent monographers place the genus in a sub-
family apart from that containing the true geese.


10


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Based on humeral characteristics, the seven available genera of
sheldrakes fall into five distinct groups: Tadorna and Casarca form
one, Chloephaga and Alopochen another, and Neochen, Cereopsis, and
Tachyeres individually the other three.
Tadorna and Casarca cannot be separated by features of the hum-
erus. Together they differ from Chloephaga and Alopochen as follows:
(1) The external tuberosity is less prominent as a result of its distal
portion lying almost flush with the shaft. (2) The external head of the
triceps is narrower and the capital shaft ridge curves inward toward
its external edge. In Alopochen and Chloephaga, where the external
head of the triceps is wider, the capital shaft ridge is straight and direc-
ted towards the median edge of the external tuberosity. (3) The distal
end of the humerus possesses characters that tend to distinguish Ta-
dorna and Casarca from Alopochen and Chloephaga, but none is con-
stant. The lack of an anconal protuberance on the entepicondyle is
the most reliable of these.
Alopochen differs from Chloephaga as follows: (1) The capital shaft
ridge is more prominent in Alopochen; correspondingly the area be-
tween the ridge and the pneumatic fossa is a much more steeply in-
clined surface in Chloephaga. (2) The internal tuberosity is less elevat-
ed in Alopochen (best observed by looking along the shaft towards the
pneumatic fossa). (3) The facet for the anterior articular ligament is a
rounded knob in Alopochen; in Chloephaga the surface is flat.
The humerus of Neochen is quite different from those of other shel-
drakes, and certain features indicate a relationship to the dabbling
ducks. (1) The depression for the external head of the triceps extends
laterally to the external tuberosity. This is characteristic of ducks
other than sheldrakes; all available sheldrake specimens have a space
between the area of muscle attachment and the tuberosity. (2) The lip
extending from the head over the impression formed by the external
head of the triceps is curved. In most dabbling ducks it is almost
straight and perpendicular to the shaft. Chloephaga and Alopochen
show curvature in this area. (3) The deltoid crest is less flaring and
more abruptly bent in the middle as in the dabbling ducks, but ex-
tends farther distally, and this is characteristic only of the sheldrakes.
(4) The head is rotated as mentioned previously. This feature is unique
to the sheldrakes among the ducks. From the characters of the humer-
us the position of Neochen remains uncertain, although its strongest
affinities do seem to lie with the sheldrakes.
The humerus of Cereopsis is more like that of the swans and geese
than any of the sheldrakes. It resembles them in the following ways:
(1) The capital shaft ridge is extremely prominent and directed towards


11







BULLETIN FLORIDA STATE MUSEUM


the head. (2) The surface for pectoral attachment on the external tub-
erosity is elevated from the shaft and, therefore, less elongated than in
sheldrakes. (3) The facet for the anterior articular ligament is less
elevated than in sheldrakes. (4) The entepicondylar prominence is
laterally produced as in swans. Cereopsis differs from the swans and
geese as follows: (1) The deltoid crest is more evenly curved through-
out its length. (2) The head blends in with the shaft instead of being
delimited by a depression on the anconal surface. Thus the features of
the humerus of Cereopsis point toward a strong affinity with the swans
and geese.
The humeral feature that best distinguishes the sheldrakes from
the other ducks, the rotation of the head, is lacking in the aberrant
Tachyeres. In sheldrakes the external tuberosity comprises more than
89 percent of the height of the head. In Tachyeres the external tuberos-
ity constitutes only 86.2 percent. Tachyeres has the following addi-
tional characteristics: (1) The excavation for the external head of the
triceps is very deep. The depth results in a prominent capital shaft
ridge directed towards the external tuberosity. The surface media to
the ridge upon which the muscle attaches is steeply inclined, and the
proximal extent of the muscle forms a deep cavity beneath the head.
(2) The internal tuberosity is bent distad so that it considerably over-
hangs the pneumatic fossa. This striking feature is most evident when
the bone is viewed from the internal side. (3) The deltoid crest has the
proximal portion concave in anconal view; the distal portion flares wide-
ly, and meets the shaft at an abrupt angle. (4) The brachial depression
is indistinct, but covers a wide area. (5) The facet for the attachment
of the extensor metacarpi radialis (a depression on the external side of
the distal end of the humerus immediately proximal to the ectepicondy-
lar prominence) is more media than in other ducks.

TRIBE ANATINI (DABBLING DUCKs). The humerus of the dabbling ducks
can be described as follows: (1) The capital shaft ridge is obsolete,
in contrast with the sheldrakes. (2) The pneumatic fossa is ovaloid and
unrimmed with heavy bone, in contrast with the perchers (see perching
ducks for additional details). (3) The pneumatic fossa is open and
contains bony struts (Woolfenden, 1959) instead of being closed as in
the pochards (except Netta and usually Metopiana), eiders, sea ducks
(except Mergus and Lophodytes), and stiff-tailed ducks.
In dabblers the ectepicondyle is equal or subequal in anconal
height to the entepicondyle when the humerus is placed on a horizontal
flat surface, palmar side down. In the pochards, including Metopiana
and Netta, the entepicondyle is distinctly higher.


12


Vol. 6







WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Dabblers differ from mergansers in the form of the internal tuber-
osity. In the mergansers, and this is essentially true of all sea ducks,
it is shorter and the length (measured perpendicular to the shaft from
the ligamental furrow to the tip) is less than the width (measured from
the capital groove to the area of attachment of the infraspinatus).
No humeral features have been found that enable the separation of
Chaulelasmus, Mareca, and Spatula from the genus Anas. Specimens
of Mareca frequently display a robust shaft and a compressed distal
condylar area, but these features do not seem consistent enough in
large series to merit generic distinction.
On the basis of the humerus alone the species Anas leucophrys de-
serves segregation in a separate genus. The distal condylar area is
grossly different from that of the 22 available species of typical dabblers
(Anas, Chaulelasmus, Mareca, Spatula). The name Callonetta, pro-
posed as a subgenus by Delacour (1936) for this little-known species
can be used (Delacour spells it Calonetta in later publications [1945,
1956]). Its humerus differs from those found in the aforementioned
genera as follows: (1) The shaft is more sigmoid than in Anas. (2) The
distal end is rotated so that the ectepicondyle is much more elevated
than the entepicondyle. (3) In anconal view the entepicondyle appears
distally elongated. In typical dabblers the entepicondyle is generally
as high as the ectepicondyle and is never distally elongated. (4) The
deltoid crest is more rounded distally from the bend, instead of being
angular as in typical dabblers. Features 1, 2, and 3, and also a robust
shaft (8.0 percent of total length) strongly oppose Delacour's suggestion
(1956) of the possible affinities of Callonetta to the pochards (wherein
the shaft varies from 6.0 to 7.0 percent). In certain perching ducks
(Nettapus, Cheniscus, and Amazonetta), and sea ducks (Histrionicus
and Clangula), however, the rotation of the condyles and thickness of
the shaft resemble that of Callonetta. Of these two tribes only the
perching ducks have the open fossa found in Callonetta.
The affinities of Malacorhynchus are inconclusive from its humeral
characteristics, which are: (1) The pneumatic fossa is closed as in the
diving tribes. (2) The rim of the pneumatic fossa is ovaloid and lacks
heavy bone, thus contrasting with typical perching ducks. (3) The
facet for the anterior articular ligament is elevated as in dabbling and
perching ducks. (4) The rotation of the condyles, which results in the
ectepicondyle being slightly higher than the entepicondyle, contrasts
with the pochards. (5) The position of the pits for the muscles that
attach to the internal surface of the entepicondyle resembles that found
only in dabbling and perching ducks.


13






BULLETIN FLORIDA STATE MUSEUM


Hymenolaimus and Merganetta have several features in common
that distinguish them from all other dabbling ducks. The fact that both
genera habitually dive may account for their similarities: (1) The
entepicondyle is less flaring and less extended distally. (2) The area
for the attachment of the external head of the triceps is more deeply
and broadly excavated. (3) The deltoid crest is reduced and more
rounded and thus less angular at the bend. (4) The bicipital crest joins
the shaft at a much wider angle than in other dabblers, particularly in
Merganetta. (5) The internal tuberosity is less produced anconally, and
possesses a distally directed flexure.
These two genera are best distinguished from each other by com-
paring the depth of the ligamental furrow. In Merganetta this is ex-
tremely shallow, more so than in any other anatid, whereas in Hymeno-
laimus it appears to be of normal depth. The brachial depression, al-
though not deep in Merganetta, covers a larger area than is character-
istic of the tribe. Lastly, Merganetta has the facet for the anterior
articular ligament less elevated than Hymenolaimus.
Rhodonessa has humeral characteristics intermediate between those
of the dabbling ducks and the closely related pochards. The following
features are worth noting: (1) The shaft is intermediate in width
(7.0 percent of total length) between dabbling ducks (average 7.44 per-
cent) and pochards (average 6.33 percent). (2) The facet for the anter-
ior articular ligament is less elevated than in dabblers, but more eleva-
ted than in pochards. (3) The entepicondyle has a more prominent pro-
cess on the anconal surface than in any other dabbling duck. In this
respect Rhodonessa resembles the pochards, for when the humerus is
viewed from this distal end with the palmar surface lying flat, the en-
tepicondyle is more elevated than the ectepicondyle. The reverse is
true of the dabbling duck.
TRIBE CAIRININI (PERCHING DUCKS). The most trenchant feature of
perching duck humeri is the rim of the open pneumatic fossa. This
tribe shows a definite trend toward a reduction of the fossa to a re-
stricted, circular opening rimmed with heavy bone. In the extremely
similar humeri of dabbling ducks the fossa becomes ovaloid by an up-
ward extension into the internal tuberosity. The shaft of the humerus
in many perching ducks tends to be more robust so that the range for
the available genera (all but Asarcornis) is from 6.7 to 8.7 percent of the
total length, with an average of 7.81. The ratio in the aberrant Plec-
tropterus is 5.7 and 6.3 percent.
Chenonetta, Nettapus, and Cheniscus are similar and can be dis-
tinguished from other perching ducks in several ways: (1) The proxi-


14


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


mal end of the humerus is inflected to give a more sigmoid appearance
of the shaft. (2) The prominent deltoid crest is more flaring and the
head is seemingly less prominent. (3) The pneumatic fossa is more re-
stricted. When the humerus is viewed from the internal side down a
line perpendicular to the shaft and passing through the internal tuber-
osity, the fossa can scarcely be seen. In other perching ducks one can
normally see into the fossa when the humerus is so orientated. (4) The
distal condyles are rotated so that in distal view the ectepicondyle is
elevated above the entepicondyle. Sarkidiornis and Amazonetta also
have this feature.
Nettapus and Cheniscus, whose humeri are indistinguishable on
qualitative features, have the entepicondylar prominence distally pro-
duced and the facet for the anterior articular ligament more flush with
the shaft than does Chenonetta. Otherwise the similarity between
these three genera is striking.
Chenonetta, Nettapus and Cheniscus share with Aix, Dendronessa,
Cairina, and Pteronetta a difference in the form of the head as com-
pared with other perchers. In these genera the depression formed by
the external head of the triceps is indistinct along the internal edge of
the external tuberosity, and blends with the external portion of the
head. In Amazonetta and Sarkidiornis the depression is distinct and
extends to the external tuberosity, as in the dabbling ducks.
Aix, Dendronessa, Cairina, and Pteronetta have additional similar-
ities in the form of the humerus. The shaft is curved in these genera
in contrast to Sarkidiornis, but the head is not inflected, in opposition to
Chenonetta, Nettapus, Cheniscus, and Amazonetta.
Cairina and Pteronetta differ from Aix and Dendronessa through
greater overhang of the lip over the capital groove. Otherwise the
humeri of these four genera are qualitatively extremely similar. Fur-
thermore, all would be difficult to separate from the typical dabblers
if it were not for differences of the fossa and the area of attachment of
the external head of the triceps. The humeri of Aix and Dendronessa
are indistinguishable.
A few minor differences in the proximal end exist between Ptero-
netta and Cairina. (1) In Pteronetta the depression for the external
head of the triceps extends farther laterally, whereas Cairina shows an
elevated area immediately medial to the external tuberosity. (2) In
Pteronetta the deltoid crest extends farther out the shaft than in
Cairina. This is best seen by comparing its distal extent with that
of the bicipital crest:
The humerus of Amazonetta can be distinguished from those of
typical dabblers quite easily. Amazonetta has the same pronounced


15







BULLETIN FLORIDA STATE MUSEUM


sigmoid curvature of the shaft, with the flaring deltoid crest and in-
flected head as do Chenonetta and Nettapus. In Amazonetta the dis-
tal condyles tend to be rotated so that in distal view the ectepicondyle
is elevated above the entepicondyle, as in Callonetta.
Certain features of the humerus of Amazonetta show greater re-
semblance to the dabbling ducks than to the perching ducks. (1) The
pneumatic fossa is ovaloid. (2) The depression for the external head of
the triceps is excavated to the external tuberosity instead of blending
with the head laterally. The humeral characteristics of Amazonetta
leave its position in the Anatinae somewhat in doubt, but certainly it
is generally distinct from Anas.
Sarkidiornis has the constricted, round pneumatic fossa that char-
acterizes the tribe, but differs from typical perching ducks in having
the depression for the external head of the triceps distinct and extend-
ing to the external tuberosity as in the dabbling ducks. Sarkidiornis
differs from all other perching ducks in that the shaft of the humerus
is very straight. The species also has the distal portion of the external
tuberosity elevated so that the plane which passes through the area of
pectoral attachment almost parallels the plane of the shaft. Further-
more, the bicipital crest is more rounded and meets the shaft at almost
a right angle.
Several humeral features of Plectropterus suggest its closer affinity
to the sheldrakes than the perching ducks. The head is rotated as in
the sheldrakes, although the external tuberosity measures less than 89
percent of the total height of the head in the two specimens available.
Another sheldrake feature is the rather prominent capital shaft ridge
directed towards the external tuberosity. The shaft of the humerus,
thick in the perching ducks, is thin in Plectropterus (5.7 to 6.3 percent
of the total length), not only thinner than in the perchers, but even
thinner than in the sheldrakes.

TRIBE AYTHYINI (POCHARDS). The important differences between the
pochards and the closely similar eiders and sea ducks are associated
with the distal end of the element. The pochards have the following
characteristics: (1) The impression for the brachialis anticus is usually
a well-formed depression with the distal medial rim sharply defined.
Stettenheim (1958) uses this feature to distinguish Aythya from similar-
sized Clangula and Lophodytes. (2) The distal condyles are rotated so
that the entepicondyle is higher than the ectepicondyle when the palmar
surface is lying flat. As a result the palmar floor of the olecranal fossa
lies almost parallel to the flat surface in the pochards, whereas in the
eiders and sea ducks a considerable angle is formed. The angle in


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


eiders and sea ducks results from pronounced rotation of the condyles
in the opposite direction from that in pochards. (3) In pochards the
intercondylar furrow is essentially confluent with the olecranal fossa
without the transverse ridge that separates them in the eiders and sea
ducks.
With the exception of the closed pneumatic fossa, the humerus of
Aythya is similar to dabbling duck humeri. However two additional
features seem useful: (1) The shaft is relatively thinner (6.0 to 6.9 per-
cent of total length, average 6.33) than in typical dabblers (6.7 to 8.4
percent, average 7.44). (2) The facet for the anterior articular ligament
is less elevated.
Humeri of species in the genus Aythya are extremely similar, vary-
ing significantly only in total length. The width of the shaft and the
width through the distal end, given as percentages of the total length,
range from 6.0 to 6.9 and from 13.9 to 15.3 respectively for 27 speci-
mens of Aythya marila. The ranges for 45 specimens of seven other
species of Aythya fall within those obtained for the one species.
Metopiana and Netta, which possess open fossae, show their affili-
ations to the genus Aythya in the shape and elevation of the anconal
portion of the entepicondyle. As previously mentioned, in distal view
the entepicondyle is higher than the ectepicondyle. In Metopiana (6.8
to 6.9) and Netta (6.7 to 7.0), the shaft is intermediate in width between
Aythya (6.33 average) and the typical dabblers (7.44 average). Ele-
vation of the facet for the anterior articular ligament is also inter-
mediate between the low one found in Aythya, and the high one of
typical dabblers.
The differences between the humeri of Metopiana and Netta are of
generic magnitude. In Metopiana the bicipital crest arises more
abruptly from the shaft, and the head is more robust than in Netta. In
Metopiana the head comprises from 7.6 to 7.8 percent of the total
length, whereas both specimens of Netta have a percentage of 6.6.
TRIBE SOMATERIINI (EIDERS). Delacour and Mayr (1945) placed the
eiders and sea ducks in one tribe. In his later work Delacour (1956)
states that the affinities of the eiders lie more with the dabbling ducks
and places them in a separate tribe near this group. Humphrey
(1958a) published evidence in support of the change.
Structurally the humeri of eiders and sea ducks are very similar.
They differ from those of the dabbling ducks in a number of significant
characters. (1) The pneumatic fossa is closed in the eiders, and with
two exceptions, in the sea ducks. (2) The internal tuberosity is short
and deep. (3) The facet for the anterior articular ligament is lower.


1961


17






BULLETIN FLORIDA STATE MUSEUM


(4) The pit for the origin of the pronator longus (the distal pit nearest
the anterior articular ligament) extends farther proximally. (5) The pit
for the origin of the pronator brevis (the most proximal of the three pits
situated on the internal side of the entepicondyle, also see Howard
[1929, fig. 21]) is situated farther distally. The last three features
reduce the area occupied by the entepicondylar prominence, a trait
characteristic of sea ducks.
Delacour and Mayr (1945) place the four eider species in one genus,
Somateria. Humphrey (1958a) agrees that Lampronetta should be
synonymized, but maintains that Polysticta is generically distinct, a
judgment followed by Delacour (1959). The form of the humerus sup-
ports this conclusion. No features of the humerus were found to sep-
arate Lampronetta from Somateria, but in Polysticta the distal end is
much more strongly rotated. As a result the anconal portion of the ex-
ternal condyle is elevated above the entepicondyle. The only other
ducks with a similar degree of rotation of the distal end are Clangula
and Histrionicus of the sea ducks. Thus the distinctness of Polysticta
brought forth by Humphrey also points to a close relationship of the
genus to certain sea ducks. Because eiders and sea ducks are similar
in the form of the humerus, the eiders are included in the discussion of
the sea ducks which follows.
TRIBE MERGINI (SEA DUCKS). The humerus shows much variation in
form in sea ducks. Two quite obvious features which seem to have
phylogenetic significance are the degree of rotation of the distal con-
dyles and the shape of the deltoid crest.
Histrionicus and Clangula, which Delacour and Mayr believe oc-
cupy a central position among sea ducks-"they lead to the scoters and
eiders on one side and to the goldeneyes and mergansers on the other"-
and Polysticta of the eiders are the only genera in the group that show
extreme rotation of the distal condyles. In distal view even the anconal
portion of the external condyle is elevated above the entepicondyle.
Polysticta differs from Clangula, and particularly from Histrionicus,
in having greater excavation of the humeral head for the external head
of the triceps. The degree of excavation in Polysticta is matched only
in Bucephala.
Clangula differs from Histrionicus, and most other genera, in that
the entepicondyle is produced distally.
The deltoid crest in scoters (Melanitta and Oidemia) and in mer-
gansers (Lophodytes, Mergellus, and Mergus) is characteristic in each
group. In scoters, in distinction to eiders and other sea ducks, the del-
toid crest extends farther distad, and its distal portion is more flaring;


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


the crest maintains a sharp edge to the most proximad point of the ex-
ternal tuberosity, whereas in other genera, and particularly the elders,
the crest ends before reaching the external tuberosity. In lateral view
the crest in scoters is gently curved and lacks the more proximal, sharp
bend found in other genera.
Oidemia differs from Melanitta only in the relative width through
the distal condyles. In Oidemia this measurement varies from 13.9 to
14.4 percent of the total length; in Melanitta the range is 14.5 to 15.8
percent.
In mergansers the deltoid crest is large and sharply angular. Typ-
ically, when the humerus of a merganser is placed palmar surface down
on a flat surface, only the angle in the middle of the crest touches the
surface. This contrasts sharply with the humerus of the closely related
Bucephala, in which the deltoid crest is small and rounded at the bend.
Mergellus is the most distinct of the merganser genera in qualita-
tive features of the humerus. The deltoid crest, although angular, is
not as large as in Mergus and Lophodytes. The pneumatic fossa is
closed, whereas it is always open (Mergus), or almost always open
(Lophodytes) in the others. Mergellus differs from the similarly-sized
Lophodytes in still other ways. The relative width of the shaft is 6.4
percent of the total length in Mergellus, from 7.1 to 7.7 percent in Lo-
phodytes. The relative width of the distal condyles in Mergellus is 14.4
percent of the total length, in Lophodytes 15.6 to 17.3 percent.
Other than size the most obvious feature separating Lophodytes and
Mergus is the shape of the humeral shaft. In Lophodytes the shaft is
distinctly more sigmoid in anconal view than in Mergus, in which it is
straighter than in most other ducks.
The humeri of the two species of Mergus examined are separable by
the width of the shaft relative to its total length (Wetmore, 1948).
Four specimens of M. merganser range from 7.0 to 7.3 percent. In 17
specimens of M. serrator the range is 5.6 to 6.9 percent.
Bucephala differs from Somateria and Lampronetta in having great-
er curvature of the shaft, and a more restricted, closed pneumatic fossa.
In Somateria, although the fossa is closed, it is rather deep.
TRIBE OXYURINI (STIFF-TAILED DucKS). The humerus of the stiff-tailed
ducks shows the tribe to be very distinct among the Anatinae. Howard
(1946) commented on the ease with which Oxyura jamaicensis can be
distinguished from all other (i.e. North American) ducks, and this spe-
cies has many features in common with the other genera assigned to the
tribe. The tribe is unique in the following ways: (1) The pneumatic
fossa is shallow, barely reaching the head, and has numerous fora-


1961


19





BULLETIN FLORIDA STATE MUSEUM


mina piercing the walls. In other ducks the fossa may be closed or
open, but if closed it is not as shallow, nor is it pierced by an abun-
dance of foramina. (2) The scar for the latissimus dorsi posterioris lies
essentially in line with the outer edge of the pectoral attachment. In
all other Anatidae the scar lies far media to the outer edge of the pec-
toral attachment. (3) The entepicondyle is reduced, as is the pit for
the flexor carpi ulnaris (the distal pit farthest from the anterior articular
ligament).
Oxyura possesses the following identifying features: (1) The surface
for the external head of the triceps is deep, and broadly excavated.
(2) The distal portion of the external tuberosity is elevated so that the
surface for pectoral attachment lies in a plane that almost parallels the
plane of the shaft. (3) The shaft is thin (5.2 to 6.0 percent of the total
length). (4) The facet for the anterior articular ligament is only slight-
ly elevated from the shaft, and is distinctly turned towards the internal
edge of the element. (5) The external condyle has a ridge extending
toward the brachial depression.
Nomonyx appears less specialized than Oxyura. It may be distin-
guished from Oxyura as follows: (1) The internal tuberosity is elongate
instead of very short. (2) The facet for the anterior articular ligament
is more elevated and faces palmad instead of internally. (3) The de-
pression for the external head of the triceps is less excavated. (4) The
distal portion of the external tuberosity is less elevated and therefore
less distinct from the shaft. The one available complete humerus has
the shaft thin (6.0 percent of total length), but thicker than in most of
the 13 specimens of Oxyura.
The humerus of Biziura shows it to be definitely a stiff-tailed duck:
(1) The pneumatic fossa is shallow and perforated. (2) The distal por-
tion of the external tuberosity is elevated from the plane of the shaft.
(3) The shaft is thin (5.5 percent of the total length). (4) The facet for
the anterior articular ligament is turned towards the internal edge of
the element.
Many features of generic magnitude occur on the humerus of
Biziura: (1) The depression for the external head of the triceps is re-
stricted to an area well below the head and media to the capital shaft
ridge. Thus the head blends in with the shaft instead of being delimit-
ed by a distinct lip as in Oxyura. (2) The external tuberosity has the
distal portion even more elevated than in Oxyura, and as a result the
area of pectoral attachment is more rounded and less elongate than in
other genera. The external tuberosity is further accentuated because
the proximal portion of the deltoid crest bends inward under the tuber-
osity. (3) The scar for the latissimus dorsi posterioris lies largely distal


20


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


to the bicipital crest. (4) The ectepicondyle is greatly reduced, without
the groove between it and the external condyle present in all other
ducks. (5) The entepicondyle is very small, and on the internal edge
only one large pit is evident. (6) The brachial depression is broad and
rounded distally. In other stiff-tails the distal end of the depression is
usually pointed. (7) The ridge extending from the palmar tip of the
external condyle, described above for Oxyura, is indistinct.
Strong evidence supports placing the genus Heteronetta with Oxy-
ura, Nomonyx, and Biziura. The humerus has the trenchant character-
istics of the tribe, namely the shallow, abundantly perforated pneumat-
ic fossa and the laterally situated scar for the latissimus dorsi posteri-
oris. The degree of development of certain features of Heteronetta
suggest it to be the least specialized member of the tribe: (1) The
entepicondyle is reduced, but not to the extreme exhibited by Oxyura
and Biziura. (2) The shaft is thin (6.3 percent of total length), but
thicker than in any other stiff-tail. (3) The facet for the anterior articu-
lar ligament is low, but not as low as in other stiff-tailed ducks. (4)
The plane of the surface for the pectoral attachment is inclined to the
plane of the shaft, more as in Anatinae other than the stiff-tailed ducks.
(5) The area of attachment of the external head of the triceps is reduced
and blends in with the head, and it lacks the depression and over-
hanging lip of the other stiff-tails. (6) The scar for the latissimus dorsi
posterioris is situated laterad, but not as far as in other stiff-tails. The
humerus of Heteronetta indicates this genus to be a link between the
quite distinct stiff-tails and some other tribe, possibly the dabbling
ducks.
Carpometacarpus
The carpometacarpus is very useful taxonomically because of its many
articulating surfaces and muscular attachments.

ANSERANATINAE
The carpometacarpus of Anseranas has several characteristics that
distinguish it from those of all other waterfowl: (1) The carpal trochlea
has the lower portion of the external rim unnotched. In all other
anatids the outer rim is distinctly notched below. (2) A large pneu-
matic foramen is present in the internal ligamental fossa. A similarly
situated foramen is present in other waterfowl, but none has it as large.
(3) The process of metacarpal I is small. (4) Metacarpal II curves
upward distally more than in other waterfowl. (5) The facet for digit
II is wider and has a more extended lower, lateral process in cor-
respondence with feature 4. (6) Metacarpal III is more curved


1961


21











TT)

!T- i,


FIGURE 2. Left carpometacarpus. Row 1: external view Anseranas semipalmata
and Cairina moschata; dorsal view Dendrocygna autumnalis, Branta bernicla, and
Anas rubripes. Row 2: external view Cygnus melancoriphus and Branta canaden-
sis; internal view Branta canadensis and Cereopsis n.hollandiae. Row 3: external
view Tadorna tadorna and Anas rubripes; internal view Anas crecca and Merga-
netta armata. Row 4: external view Aythya affinis and Clangula hyemalis;
ventral view Bucephala albeola and Oxyura jamaicensis.


1) A Pm NN- -


'ur~Li-r"


r






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


throughout its length, particularly distally. (7) Metacarpal III is un-
grooved on the lower proximal surface. (8) The facet for digit III
protudes farther distally. In most other anatids this facet does not
extend beyond that for digit II.

ANSERINAE
Two traits seem characteristic of the Anserinae: (1) The upper sur-
face of metacarpal II, and particularly the distal half, is flat and the
angle formed with the external surface is correspondingly rather sharp.
In the Anatinae the upper surface is rounded, without sharp angles.
(2) The extensor attachment is confined to the tip of the short, but high,
process of metacarpal I. In the Anatinae the extensor attachment is
longer and extends distally onto the distal edge of the process.
TRIBE DENDROCYGNINI (WHISTLING DUCKS). The thin, elongate carpo-
metacarpus of whistling ducks has the following three features to dis-
tinguish it from all other anatids: (1) Metacarpal II in dorsal view is
strikingly incurved. (2) The external rim of the carpal trochlea is
only slightly notched. In all other waterfowl, except Anseranas, the
external rim is notched distinctly. This character may be evidence of
the primitive position of the whistling ducks. (3) A prominent neck is
present between the carpal trochlea and metacarpal III.
TRIBE ANSERINI (SWANS AND GEESE). The carpometacarpi of swans
and geese agree in: (1) Metacarpal III has a distally progressive ro-
tation toward the medial side. (2) The pollical facet has a small lateral
articulating surface.
Swans may be distinguished from geese by several carpometacarpal
features: (1) In lateral view the external rim of the carpal trochlea
slopes sharply downward from the process of metacarpal I. In geese
the angle between the posterior edge of the process of metacarpal I
and the upper, external rim of the carpal trochlea is smaller. (2) The
pit on the internal side below and distal to the pisiform process is sep-
arated by a raised area from the intermetacarpal space. (3) The pro-
cess of metacarpal I is lower and has a proximal edge that usually
slopes toward the carpal trochlea. In geese the process is higher and
the proximal edge is nearly perpendicular to the shaft. (4) Metacarpal
II has only a slight depression on the external surface immediately
proximal to the facet for digit II; in geese the depression is deeper.
(5) The external rim of the facet for digit II is widely rounded; in geese
this edge is almost straight.
Coscoroba resembles the true swans in all five of these character-
istics. It can be separated from them by differences in the lower,


1961


23






BULLETIN FLORIDA STATE MUSEUM


distal portion of the carpal trochlea. (1) The cuneiform fossa (Brod-
korb, 1958b), which lies between the rims of the carpal trochlea dis-
tally, is delimited proximally by a ridge that extends medially from
the external rim of the carpal trochlea. In true swans the ridge is
lacking and the fossa extends proximally between the two rims.
Howard (1946) lists three criteria for separating the carpometacarpi
of Olor and Cygnus; all seem weak in the series of specimens I have
studied. Listed in a sequence of decreasing usefulness these are: (1)
Cygnus has the external crest of the trochlea short, and the lobe at its
distal edge appears aborted in comparison with Olor. (2) Cygnus has
the process of metacarpal I straighter and more evenly swollen at the
tip, whereas in Olor the process inclines more definitely toward the
inner side. (3) Cygnus has the area below the pisiform process exca-
vated into a distinct pitlike depression, the posterior rim of which is
prominent. In Olor the area is roughened, sometimes depressed, but
it tends to slope away toward the posterior face without an intervening
rim.
Additional criteria were found more useful in my series: (4) The
cuneiform fossa is deeper, and has a distinct proximal and medial rim in
Cygnus. In Olor the rim is indistinct, the fossa gradually inclining to
the surrounding areas. (5) Metacarpal I has a deeper depression on the
external surface immediately proximal to the facet for digit II in
Cygnus, and thereby more closely resembles geese. In Olor this area is
noticeably shallower. Chenopis is similar to Cygnus in all of the char-
acteristics discussed above.
No criteria of the carpometacarpus are apparent to enable qualita-
tive separation of the several genera of true geese (Anser, Cygnopsis,
Chen, Philacte, Eulabeia, Branta, Nesochen). The shorter, broader
facet for digit III attributed to Chen (Miller, 1937) is not constant.
Externally the true geese strongly resemble several genera assigned
to the sheldrake tribe by Delacour and Mayr (1945). A number of
carpometacarpal features support the allocation of these superficially
gooselike species of the genera Chloephaga, Neochen, and Alopochen
to a position near the sheldrakes Tadorna and Casarca, as well as
nearer the other duck genera. The following four characteristics of
true geese serve to separate them from the sheldrakes: (1) The ex-
ternal rim of the carpal trochlea has the upper portion extending proxi-
mally before curving downward. (2) The external rim of the carpal
trochlea is shallowly notched below. In sheldrakes the notch is notice-
ably deeper, as is generally true of all ducks. (3) The internal rim
of the carpal trochlea is less rounded and usually grades more smoothly
into the ridge of bone lying distal to it. In sheldrakes the more round-


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


ed rim falls off sharply. (4) The process of metacarpal I in lateral view
is lower; the height through the process ranges from 19.7 to 24.4 per-
cent of the total length of the carpometacarpus. In sheldrakes the pro-
cess is typically higher (23.3 to 28.6 percent), a feature that Miller
(1937) uses to separate Chlo phaga from the North American genera
of true geese.
The process of metacarpal I frequently has a rugose cap in both
geese and sheldrakes. Shufeldt (1892) attributes this condition to dis-
ease; Miller (1937) thinks its frequency of occurrence makes a patho-
logical origin unlikely. Many waterfowl commonly fight with their
wings, and the occurrence of the knob may well be correlated with this
behavior. Chloephaga, Alopochen, and Neochen almost always have
the knob, and all are listed as very quarrelsome by Delacour and Mayr.
Caps also occur on the carpometacarpi of Cygnus, Chenopis, Branta,
Anser, Tachyeres (large), Hymenolaimus (large), Merganetta (large),
and Sarkidiornis.
Two genera, Merganetta and Plectropterus, have developed carpal
spurs (Rand, 1954), and the latter is known to be aggressive in captiv-
ity. In addition to a metacarpal I process seemingly designed for a
spur, one specimen of Merganetta, labelled a juvenile male (U.S.N.M.
346808) possesses a sharp claw 3 mm. in length on the tip of the pollex,
a fact apparently unrecorded in the literature (Fisher, 1940).

ANATINAE
The Anatinae can be distinguished from the Anseranatinae and
Anserinae by two carpometacarpal features: (1) The upper surface
of metacarpal II is rounded, without sharp angles. (2) The extensor
attachment on the tip of the process of metacarpal I is longer and ex-
tends distally onto the anterior edge of the process (a weak character
for sheldrakes).
With the ducks the most critical region of the carpometacarpus is the
external surface of the trochlea. The shape and location of the attach-
ments for two ligaments and the ridges on the bone associated there-
with are particularly significant. Howard (1929) labels an external lig-
amental attachment on her drawings. In waterfowl the ligament at-
tached theron extends to the cuneiform (ulnare). Another place of liga-
mental attachment from which a ligament extends to the scapholunar
(radiale) lies distal to the one labelled in Howard. The external scapho-
lunar ligament crosses over the external cuneiform ligament.
Delacour (1954, 1956, 1959) divides the Anatinae into seven tribes.
Features of the carpometacarpus separate the subfamily into five
groups: (1) sheldrakes, (2) dabbling and perching ducks, (3) pochards,


1961


25







BULLETIN FLORIDA STATE MUSEUM


(4) eiders and sea ducks, and (5) stiff-tailed ducks. Although the carpo-
metacarpi of dabbling and perching ducks (group 2), pochards (group
3), and eiders and sea ducks (group 4) are very similar, combinations
of the characteristics listed at the beginning of each should make pos-
sible the proper determination of all specimens, assuming comparative
material is available.

TRIBE TADORNINI (SHELDRAKES). Sheldrakes have three features of the
carpometacarpus that distinguish them from other ducks; all three fea-
tures are common to the true geese, perhaps an indication of an in-
termediate position of the sheldrakes between the geese and ducks:
(1) The external scapholunar ligamental attachment is broad, usually
prominent, and situated higher and more distal than in other ducks. It
always lies distal to the ridge that extends from the external cuneiform
ligamental attachment to the proximal fornix (the point of fusion of
metacarpal II and III proximally). (2) The lobe at the distal end of
the external rim of the carpal trochlea is larger. (3) The process of
metacarpal I is higher, shorter, and frequently has a rugose cap.
The carpometacarpus of Cereopsis resembles those of the Anserini
of Delacour and Mayr (1945). Two unique features distinguish the
species: (1) In the process of metacarpal I the proximal edge slopes
forward, and the distal edge is more concave so that the tip is more
pointed. (2) The distal metacarpal symphysis is approximately twice
as long as that found in geese.
With Cereopsis removed because of its resemblance to the true
geese, three major groups remain within the sheldrakes: Chloephaga,
Alopochen, and Neochen form one group; Tadorna and Casarca an-
other; and Tachyeres the third.
No qualitative features separating Casarca from Tadorna are evi-
dent, but the two as a unit can be distinguished from Chloephaga,
Alopochen, and Neochen by a combination of characteristics: (1)
The process of metacarpal I is lower, thinner in proximal view, nearly
perpendicular to the shaft, and usually without a rugose cap. In the
other three genera the process is higher, thicker, bent proximally, and
frequently it possesses a rugose cap. (2) The cuneiform fossa is longer
and extends proximally beyond the lobe that marks the distal extent
of the external rim of the carpal trochlea. In the others the fossa ends
rather abruptly at a point opposite the lobe. (3) The tuberosity of
metacarpal II is more prominent in dorsal view, and does not rise so
high up from the shaft in the three gooselike genera. (4) The facet for
digit III falls decidedly short of the facet for digit II. In the other
three genera the two facets are almost equal in distal extent.


Vol. 6








WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Alopochen seems the most distinct of the three gooselike genera.
The following features set it apart from the other two: (1) The external
surface situated below the external cuneiform ligamental attachment
is deeply grooved. (2) The anterior carpal fossa is shallow. In Chlo&-
phaga and Neochen the anterior carpal fossa forms an obvious pit at
the edge of the carpal trochlea. (3) The flexor attachment is more dis-
tal. In the other two genera the flexor attachment lies farther proxi-
mad. A ratio of the distance to the midpoint of the flexor attachment
from the proximal end divided by the carpometacarpal length ranges
from 27.5 to 30.3 percent with only 1 specimen of 8 having a greater
percentage than 29.3. The same ratio ranges from 29.5 to 31.4 in 3
specimens of Alopochen.
Although the 3 genera of gooselike sheldrakes are very similar,
Neochen seems slightly closer to Chloephaga. The flexor attachment
ratio is 28.6 percent for the one specimen, and the anterior carpal fossa
is deep. The groove below the external cuneiform ligamental attach-
ment, however, seems deeper than in most specimens of Chloephaga.
Delacour (1954) includes Tachyeres in the sheldrakes, but it dif-
fers from that tribe in two diagnostic features of the carpometacarpus:
(1) The external scapholunar ligamental attachment lies on the diago-
nal ridge that passes from the external cuneiform ligamental attach-
ment to the proximal fornix. In sheldrakes the attachment lies distal
to the ridge. (2) The lobe at the distal end of the external rim of the
carpal trochlea is essentially lacking. All true sheldrakes have a prom-
inent lobe. In Tachyeres the process of metacarpal I is long as in most
ducks. The process appears high, as in sheldrakes, but this may be
due to foreshortening of the element, correlated with a flightless con-
dition. Although a rugose cap is present as is typical of sheldrakes,
this condition is found sporadically throughout the Anatidae.
TRIBES ANATINI AND CAIRININI (DABBLING AND PERCHING DUCKS). (1)
The distal portion of the external rim of the carpal trochlea has a
noticeable prominence, but it is usually smaller than that found in eiders
and sea ducks. The lateral outline of the area is convex. (2) The cune-
iform fossa is deeper than in pochards, but usually shallower than in
eiders and sea ducks. (3) The external scapholunar ligamental attach-
ment is prominent and larger than in pochards, and usually lies on a
conspicuous ridge that extends from the external cuneiform ligamental
attachment to the proximal fornix. (4) The flexor attachment extends
distally beyond the proximal fornix. The extent of the proximal end of
the flexor attachment is variable. (5) The process of metacarpal I is
higher and straighter than in eiders and sea ducks.


27







BULLETIN FLORIDA STATE MUSEUM


TRIBE ANATINI (DABBLING DUCKS). Features of the carpometacarpus
do not support the recognition of Chaulelasmus, Mareca, and Spatula
as distinct genera. Some differences do occur, but none was found that
has a high constancy. Many characters that appear useful in a small
series break down when additional specimens are compared. In com-
paring 16 specimens of Mareca with 7 of Chaulelasmus, 5 of Spatula,
and over 40 of numerous species of Anas, Mareca proved the most dis-
tinct of the three, some specimens being assignable without compara-
tive study. The straight, robust shaft and the recessed condition of
the facet for digit III are the best criteria. However, not all the speci-
mens could be identified, even with the aid of comparative material.
Wetmore (1944) and Brodkorb (1958a) mention that the carpomet-
acarpus of Anas (Nettion) carolinensis can be separated from that of
Anas (Querquedula) discors as follows: (1) Nettion has the anterior
carpal fossa very shallow, whereas it is deeply excavated in Querque-
dula. (2) In Nettion the length of the distal metacarpal symphysis is
6.0 mm. or less, whereas in Querquedula it is approximately 7 mm. or
more. The feature pertaining to the depth of the anterior carpal fossa
readily separates 17 of 25 specimens (Nettion 9, Querquedula discors
10, Q. cyanoptera 3, Q. quequedula 3), but for 3 (Nettion 2, Q. discors
1) the character is reversed, and in 5 others it appears intermediate.
Just how Wetmore measured the distal metacarpal symphysis is un-
certain, but some of the available specimens of Querquedula apparently
measure less than 7 mm., so even this character is not entirely constant.
Qualitative features of the carpometacarpus indicate that 4 of the
available genera of dabbling ducks are distinct from Anas, namely
Callonetta, Malacorhynchus, Hymenolaimus, and Merganetta.
Callonetta has three distinctive features: (1) The process of meta-
carpal I has its distal edge sloping sharply proximally, and has only a
small attachment surface at the tip. (2) The base of metacarpal III is
narrower in ventral view. (3) The external rim of the carpal trochlea
is slightly longer and narrower.
Malacorhynchus also has three criteria that distinguish it from typi-
cal dabblers: (1) The process of metacarpal I appears decidedly shorter
in lateral view and has only a small extensor surface. (2) The proximal
end of metacarpal III is very narrow and does not extend laterally
around the cuneiform fossa. (3) The shaft of metacarpal II is notice-
ably thinner in dorsal view .
Hymenolaimus is very different from other dabbling ducks: (1) The
internal rim of the carpal trochlea is enlarged; it curves farther down-
ward and is thicker. (2) The groove between the rims of the carpal
trochlea and the cuneiform fossa is very deep. (3) The external scapho-


28


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


lunar ligamental attachment is larger and situated farther distally. In
this respect Hymenolaimus resembles the sheldrakes. (4) The external
portion of the proximal end of metacarpal III fuses with metacarpal II
farther distad. (5) The tuberosity of metacarpal II is reduced. (6) The
facet for digit III is enlarged with the lateral end bent downward and
both ends extended distally. (7) A rugose knob is present on the pro-
cess of metacarpal I. Although present in many distantly related water-
fowl, a knob is most typical of the sheldrakes.
The very short carpometacarpus of Merganetta resembles that of
Hymenolaimus in a number of features. As both are inhabitants of
mountain streams, convergence of some features might be expected
The following characteristics distinguish Merganetta: (1) Both rims of
the carpal trochlea are enlarged, and especially the internal one; they
curve farther downward, and the internal rim is thickened. (2) The
groove between the rims of the carpal trochlea and the cuneiform fossa
is very deep. (3) The proximal end of metacarpal III is narrower and
does not extend so far laterad. (4) The tuberosity of metacarpal II is
greatly reduced. (5) The facet for digit II has the external edge more
rounded. (6) The facet for digit III is distally produced. (7) The pro-
cess of metacarpal I is larger, curves sharply proximad, and sometimes
has a large knob.
TRIBE CAIRININI (PERCHING DUCKS). The perching ducks are only weak-
ly differentiated from the dabblers. Two features of the carpometacar-
pus are somewhat useful in separating the tribes: (1) The external scaph-
olunar ligamental attachment tends to be obscure. (2) The process of
metacarpal I tends to be higher, shorter, and straighter.
Features of the carpometacarpus of Plectropterus indicate the genus
is a sheldrake and not a perching duck: (1) The external scapholunar
ligamental attachment is situated distal to the ridge that passes from
the external cuneiform ligamental attachment to the proximal fornix.
This feature is typical of the sheldrakes. (2) The lobe at the distal end
of the external rim of the carpal trochlea is large. In ducks other than
sheldrakes, the lobe is relatively small or even absent.
Although Plectropterus does not have the enlargement of metacar-
pal I typical of the sheldrakes, a process of the scapholunar (figured
in Rand, 1954) serves its quarrelsome nature.
On the basis of carpometacarpal features, the two most distinct of
the remaining genera are Sarkidiornis and Pteronetta. Cairina, Cheno-
netta, Aix, and Dendronessa are all very similar to one another.
Sarkidiornis can be characterized as follows: (1) Metacarpal I is
located farther distad with the highest point of its process opposite the


1961


29






BULLETIN FLORIDA STATE MUSEUM


pisiform process. In other perchers the peak is proximal to the pisi-
form, and the anterior carpal fossa is more extensive. (2) The external
rim of the carpal trochlea is rounded proximally. In the others the rim
tends to be acuminate, the point occurring immediately proximal to the
external cuneiform ligamental attachment. (3) The groove on the ex-
ternal surface below the external cuneiform ligamental attachment is
deeper.
Pteronetta is rather easily distinguished from other perching ducks,
including Cairina: (1) The process of metacarpal I is higher. (2) The
curve of the internal rim of the carpal trochlea is situated so that the
lowest point underlies the pisiform process, whereas in the others the
lowest point is more proximal.
The large, robust carpometacarpus of Cairina has one distinctive fea-
ture: The process of metacarpal I is slightly excavated by a depression
that lies along the external edge of the base.
No qualitative features useful in distinguishing Aix, Dendronessa
and Chenonetta were found.
Nettapus and Cheniscus, for which I find no mutually exclusive
characteristics, differ from other perching ducks in the following way:
(1) The prominence proximal to the external cuneiform ligamental at-
tachment is higher and extends proximally to the posterior rim. In
other perchers it is lower and it terminates distal to the proximal rim.
Features of the carpometacarpus of Amazonetta strongly support
its recognition as a genus distinct from Anas. The process of metacar-
pal I is higher and straighter, a feature characteristic of the perching
ducks. In addition, the external rim of the carpal trochlea appears
longer and narrower than in Anas. Separating Amazonetta from other
perchers, and the dabblers, is the facet for digit III that is reduced in
size and recessed; thus it does not extend distally as far as the facet for
digit II.

TRIBE AYTHINI (POCHARDS). The carpometacarpus of pochards is quite
distinct with the following characteristics: (1) The distal portion of
the external rim of the carpal trochlea is usually without a swelling,
and generally so greatly reduced that the outline in lateral view is con-
cave. (2) The cuneiform fossa is shallow. (3) The external scapho-
lunar ligamental attachment is usually prominent, but small. The
diagonal ridge from the external cuneiform ligamental attachment to
the proximal fornix is usually obscure. (4) The flexor attachment al-
ways lies entirely proximal to the proximal fornix. (5) The process of
metacarpal I is high and straight as in the dabblers.


Vol. 6


30






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Metopiana and Netta are near Aythya, especially as indicated by the
position of the flexor attachment, but certain features of the carpomet-
acarpus indicate an intermediate position between Aythya and the
dabblers: (1) The bone is shorter and more robust than in Aythya.
(2) The process of metacarpal I is straighter. In Aythya the process
curves more proximad. (3) The distal portion of the external rim of
the carpal trochlea is more prominent. The area is more reduced in
Aythya. (4) The region on the external surface, situated proximal to
the external cuneiform ligamental attachment, is larger. In Aythya
this area is much reduced.
The carpometacarpi of Metopiana and Netta are very similar, but
most individuals can be separated by the tuberosity of metacarpal II
and the external rim of the facet for digit II which, in dorsal view, are
produced farther laterally in Metopiana than in Netta.
It is unfortunate that no carpometacarpus of Rhodonessa is available
because its humeral features indicate this genus belongs with the
pochards and not with the dabblers.

TRIBES SOMATERIINI AND MERGINI (EIDERS AND SEA DUCKS). Eiders and
sea ducks form a group easily distinguished from the pochards. The
two as a unit seem more like the dabblers, and particularly the perch-
ers, in carpometacarpal features. The following distinguishing char-
acteristics were noted: (1) The distal portion of the external rim of the
carpal trochlea has a prominent swelling that is usually larger than in
dabblers and perchers. (2) The cuneiform fossa is deeper than in the
other groups, and it frequently excavates under or around the internal
rim of the carpal trochlea. (3) The external scapholunar ligamental
attachment is obscure, and the diagonal ridge is frequently absent.
(4) The flexor attachment is variable with the genera. (5) The process
of metacarpal I is lower, wider, and curved proximally. This feature
is not useful for separating Bucephala, Lophodytes, or Mergellus, but
is extremely useful for the other genera.
Examination of the carpometacarpi of 70 specimens of eiders and
sea ducks reveals two basic facts: (1) The eiders show greater similar-
ity to the sea ducks, and particularly to the scoters and Histrionicus,
than to the dabblers; (2) the most obvious division of the genera is
into two units, one containing Bucephala and the mergansers, the other
the eiders, scoters, Histrionicus, and Clangula. This same division is
also evident from features of the humerus.
The important features for separating the two units are found in
the process of metacarpal I, and in the position and shape of the pollical
facet. In Bucephala and the mergansers the process tends to be higher,


1961


31







BULLETIN FLORIDA STATE MUSEUM


and the extensor attachment on the tip is shorter. In the other group
of genera the process is lower, longer in lateral view, and the extensor
attachment extends down the sloping distal edge of the process. These
features are most distinct in Bucephala, Lophodytes, and Mergellus at
one extreme, and Clangula at the other. Some specimens of Mergus
are very similar to certain scoters and eiders, but in Bucephala and the
mergansers the pollical facet lies in line with or proximal to the internal
rim of the carpal trochlea. In the other genera the pollical facet lies
distal to the internal rim of the carpal trochlea. Furthermore, Buce-
phala and the mergansers have only a small lateral lobe on the pollical
facet, best compared in proximal view. In the other genera the lobe
is larger and has a prominent pit or groove between it and the shaft of
metacarpal II. These characteristics permit 100 percent separation
between Bucephala and the mergansers and the remaining sea ducks.
With some features the division within the Bucephala and mergan-
ser group appears to lie between Bucephala and the mergansers, but
with others the break occurs between Mergus and the other three gen-
era. This is the case with humeral features, which indicates that Buce-
phala and the mergansers have been previously placed in separate taxa
only because of such plastic features as the shape of the bill.
A basic difference in the shape of the process of metacarpal I di-
vides the sea ducks into two groups. One of these groups, Bucephala
and the mergansers, shows significant differences in the relative height
of the process. In 18 specimens of Bacephala, Lophodytes, and Mer-
gellus the range for the height through the process of metacarpal I is
22.5 to 23.9 percent of the total length of the bone. In 19 specimens of
Mergus (17 M. serrator, 2 M. merganser) the range is from 21.0 to 22.6
percent, except for one adult M. serrator which measures 17.9 percent.
Only one individual of the latter group overlaps the minimum for the
other genera. Of the 17 available specimens of M. serrator, 14 are from
Florida and all are immature birds. It seems likely from comparison
with adult birds that the ratio would be more significant if the sample
were not biased in respect to age.
The small size of the lobe at the distal end of the carpal trochlea
separates Bucephala from the mergansers. In Lophodytes, Mergellus,
and Mergus the lobe is relatively large. An additional feature useful
for separating Bucephala from Mergus is the structure of the pisiform
process. In proximal view it curves sharply upward in Bucephala,
forming a deep groove for the flexor digitorum profundus. In Mergus
the pisiform process is directed medially, forming more of a shelf than
a groove. Specimens of Lophodytes and Mergellus are intermediate
for this feature.


Vol. 6





WOOLFENDEN: OSTEOLOGY OF WATERFOWL


With Mergus distinguished by the relative height of the process of
metacarpal I, the best characters for separating Bucephala from Lopho-
dytes and Mergellus are: (1) the feature pertaining to the external
rim of the carpal trochlea mentioned above, and (2) the shape of the
facet for digit II. In Bucephala the external portion of the facet for
digit II is larger and extends farther down into the groove between the
facets for digits II and III. In Lophodytes and Mergellus it is smaller
and does not extend down as far. No valid feature for separating Mer-
gellus from Lophodytes was found on the carpometacarpus.
Of the remaining members of the eider and sea duck group, Clangula
seems the most distinct. It has the following characteristics: (1) The
process of metacarpal I is very low, with the distal edge thick and
curving sharply proximally. (2) The carpal trochlea is depressed; its
external rim forms only a slight angle with the trend of the shaft; the
internal rim has only a relatively small depression between it and the
base of metacarpal III. (3) The pit distal to and below the pisiform
process is very deep. (4) The tuberosity of metacarpal II is situated
more medially, and as a result the external edge of the facet for digit
II appears more rounded. (5) The shaft of metacarpal II is robust (7.8
to 8.8 percent of the total length). The range for the others is 6.5 to 7.9,
except for Histrionicus which measures 8.0 percent
Two characteristics of the eiders separate them from the scoters and
Histrionicus: (1) The flexor attachment is nearly twice as long as in
the others, and is situated farther distad. (2) The upper surface of the
shaft of metacarpal II in medial view is arched.
The carpometacarpus of Lampronetta appears indistinguishable
from that of Somateria, but Polysticta differs from both in: (1) The
notch in the external rim of the carpal trochlea is smaller in ventral
view. (2) The lobe immediately distal to the notch is smaller. (3) The
cuneiform fossa is shallower.
The carpometacarpus of Oidemia is slimmer than that of Melanitta
(width of metacarpal II relative to the total length 6.5 to 7.1 percent
in Oidemia, 7.0 to 7.9 percent in Melanitta), but otherwise it appears
indistinguishable from that genus. Histrionicus has a thick shaft of
metacarpal II (8.0 percent of the total length), and a larger lobe at the
distal end of the external rim of the carpal trochlea.

TRIBE OXYURINI (STIFF-TAILED DUCKS). The stiff-tailed ducks are the
easiest of the Anatinae to define on the basis of the carpometacarpus:
(1) The distal margin of the internal rim of the carpal trochlea appears
nearly parallel to the shaft in ventral view. In the others the rim is
deflected laterally. (2) Metacarpal III is narrower at the proximal end.


1961


33






BULLETIN FLORIDA STATE MUSEUM


In members of the other four groups metacarpal III widens at the prox-
imal end and thus reaches, or virtually reaches, the external side of the
element. (3) The area on the external surface below the external liga-
mental attachments is deeply grooved. Although a groove is present in
other ducks it is not nearly as deep. (4) The facet for digit II is nar-
row, crescent-shaped, and has the lower margin concave (Heteronetta
is an exception). In the other ducks the facet is broader, and the lower
margin is nearly straight.
Features of the carpometacarpus strongly support the close rela-
tionship of Heteronetta, Nomonyx, Oxyura, and Biziura pointed out by
Delacour and Mayr (1945). Heteronetta is the least specialized mem-
ber of the tribe. The features that separate it from the other stiff-tails
are generally those found in ducks of other tribes: (1) The process of
metacarpal I is higher, and in lateral view, noticeably narrower. (2)
The distal margin of the internal rim of the carpal trochlea is deflected
laterally in ventral view. In other stiff-tails the process is nearly paral-
lel to the shaft; in other tribes it is even more deflected than in Heter-
onetta. (3) The facet for digit II is broadly rounded externally and has
the lower margin straight. (4) The tuberosity of metacarpal II is
smaller. (5) The prominence on the internal edge at the proximal end
of metacarpal III is situated nearer to the proximal fornix. In other
stiff-tails it lies more proximad.
Nomonyx resembles Oxyura less than it does Biziura in features of
the carpometacarpus. It can be separated from these two genera by
the following features, all of which seem to indicate a lesser degree of
specialization: (1) The process of metacarpal I is noticeably narrower
in lateral view. (2) The distal margin of the internal rim of the carpal
trochlea in ventral view has a slight lateral deflection greater than that
found in Oxyura and Biziura but less than in Heteronetta. (3) The
tuberosity of metacarpal II is smaller. (4) The external rim of the
carpal trochlea is not as deeply grooved as in other stiff-tails.
The following carpometacarpal features separate Biziura from
Oxyura: (1) The external rim of the carpal trochlea is extremely deep-
ly grooved, more so than in all other anatids, so that the bottom of the
cuneiform fossa can be seen in lateral view. (2) The distal portion of
the internal rim of the carpal trochlea is thickened. In Oxyura the rim
is of uniform thickness throughout. (3) The tuberosity of metacarpal
II curves more laterad.
Sternum
The sternum has received an exaggerated amount of attention from
avian taxonomists. It is not as useful as the humerus, carpometacarpus,


34


Vol. 6







1961 WOOLFENDEN: OSTEOLOGY OF WATERFOWL 35








t

I-










: I ,




























FIGURE 3. Sternum, dorsal view. Top row: Anseranas semipalmata, Dendrocygna
autumnalis, Cygnus olor, Branta canadensis. Middle row: Cereopsis n.hollandiae,
Alopochen aegyptiaca, Anas fulvigula, Merganetta armata. Bottom row: Aythya
valisineria, Clangula hyemalis, Oxyura jamaicensis.






BULLETIN FLORIDA STATE MUSEUM


or coracoid; however, some features of phylogenetic significance do
occur. Certain structural features of the sternum and pectoral girdle
may be better understood by reference to the ligaments described in
the Appendix.
The posterior margin of the sternum varies considerably. Most
Anatidae have sternal notches, but in a few genera the notches are
characteristically ossified posteriorly to form fenestrae. Other genera
may, on occasions, have one or both notches so enclosed.

ANSERANATINAE
The primitive Anseranas is easily distinguished from all other anatids
by the following criteria, the first five of which are unique among the
waterfowl: (1) The costal margin is over 50 percent of the length of
the basin (measured from the dorsal sulcal lip to the postpectoral line).
(2) The sternal basin is deep. (3) The dorsal surface of the sternal plate
is pierced by numerous foramina and crossed by transverse ridges. (4)
The sternum is trilobed posteriorly, because of very shallow sternal
notches and a rounded xiphisternum. (5) A stout median bar extends
from the dorsal sulcal lip into the basin. (6) The dorsal and ventral
manubrial spines are lacking.

ANSERINAE
The Anserinae can be distinguished from the Anseranatinae in the fol-
lowing ways: (1) The costal margin is shorter, always less than 50 per-
cent of the basin length. (2) The sternal basin is shallower. (3) The
pneumatic foramina are confined to the area posterior and ventral to
the dorsal sulcal lip, and to the anterior median portion of the basin.
(4) The xiphisternum flares laterally; its posterior margin is truncate or
slightly concave, and the sternal notches are deeper. (5) There is no
stout bar as described for Anseranas.
The Anserinae can be distinguished from the Anatinae as follows:
The dorsal sulcal lip overhangs the sternal basin medially, and forms
a large concavity at the anterior end of the sternal plate. The over-
hanging lip and the rather prominent costal margins cause the sternal
basin to appear deeper. This character is least developed in Nesochen.
TRIBE DENDROCYGNINI (WHISTLING DUCKS). The sternum of whistling
ducks shares the greatest number of similarities with that of the pied
goose. The costal margin is almost as long as in Anseranas, the sternal
basin is almost as deep, and the manubrial spines are lacking. Den-
drocygna differs from Anseranas in the characteristics listed for the
Anserinae; numbers 1, 4 ,and 5 are particularly useful. The whistling


36


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


ducks can be distinguished from the swans and geese by their lack of
a ventral manubrial spine.

TRIBE ANSERINI (SWANS AND GEESE). Swans and geese can be separat-
ed into two very distinct units on the basis of the sternum. Swans and
Coscoroba form one group, and geese form the other. The sterna of
these two units are so different as to suggest they might be treated as
separate tribes.
The sternum of swans is unique in the position of the intermuscular
line delimiting the supracoracoideus from the pectoralis superficialis as
noted by Stejneger (1882). In swans the line extends along the sternal
plate only a short distance, usually less than 75 percent of the carinal
length, before it curves down onto the carina. In all other waterfowl
the intermuscular line extends along the plate essentially to the poster-
ior end of the carina. The reduction in the relative length of the line
is indicative of the reduction of the supracoracoideus muscle. Further
indication of a reduction in this muscle is apparent when the sternum
is viewed in ventral aspect. In swans the intermuscular line angles
sharply toward the carina; in geese the line essentially parallels the
carina throughout its length.
The supracoracoideus functions to raise the wing. In the Catharti-
dae, Fisher (1946) associates a reduced supracoracoideus with a de-
crease in speed of wing flapping. It seems likely that the same princi-
ple applies to the swans, which also have a slow wing beat.
The swans are further distinguished as follows: (1) The sternal
notches are shallow. (2) The posterior lateral processes rarely extend
beyond the xiphisternum. (3) The posterior lateral processes are near-
ly in a line with the costal margin. (4) The costal margin is elongate,
forming from 40 to 50 percent of the basin length. (5) A ventral man-
ubrial spine is present which serves to distinguish swans from Anseranas
and Dendrocygna. (6) A pit is present in the dorsal portion of the
anterior carinal margin in some specimens of all species. In Olor
columbianus, 0. buccinator, 0. cygnus, and 0. bewickii the pit becomes
a huge cavern for a loop of the trachea. In Cygnus olor, C. melan-
coriphus, and Chenopis the pit is small or absent, and does not contain
the trachea.
Only one feature of the sternum, additional to the cavern for the
tracheal loop, supports the recognition of Olor as distinct from Cygnus,
and this may be a result of widening of the carina in Olor. The pos-
terior portion of the pectoralis superficialis lies close to the carina in
Cygnus, but far laterad to the carina in Olor.


37






38 BULLETIN FLORIDA STATE MUSEUM Vol. 6

The sternum of Coscoroba indicates it is closely related to the
swans. The intermuscular line, although more extensive than in the
true swans, curves down onto the carina well anterior to its posterior
termination. In ventral view the line gives additional indication of a
reduction of the supracoracoideus by distinctly angling toward the
carina throughout its length as shown in Stejneger (1882). Further
evidence for considering Coscoroba near the swans comes from the
fact that some specimens possess a pit in the dorsal portion of the ca-
rinal margin. Coscoroba can be distinguished from the true swans by
the following criteria: (1) The intermuscular line extends beyond 75
percent of the carinal length (usually about 90 percent). (2) The pos-
terior lateral processes extend well beyond the xiphisternum. Both
features are figured in Stejneger (1882).
Of all the Anserinae, the true geese are closest to the Anatinae.
Geese may be distinguished from Anseranas and other Anserinae by:
(1) The costal margin is less extensive (usually less than 40 percent of
the basin length). (2) The sternal notches are deeper (more than 33
percent of the basin length). (3) The posterior lateral processes flare
from the costal margins. (4) The xiphisternum is normally widened
posteriorly. (5) A dorsal manubrial spine is present. In other Anser-
inae and in Anseranas the notch is enlarged and eliminates the spine.
These characters, except the last, are also present in the Anatinae.
The sterna of geese show little generic variation. Miller (1937) in
his comparison of Nesochen with Branta, Anser, Chen and Philacte
found several features to distinguish Nesochen, but no constant char-
acters to separate the remaining four genera from one another.
Nesochen is characterized by the following features: (1) The ster-
num is narrower, the width (narrowest extent between the costal mar-
gins) varying from t,7 to 40 percent of the basin length. In all other
geese the minimum is over 41 percent. (2) The carina is visibly lower.
As Miller states, the difference in carinal height is evident only posterior
to the apex where no fixed points for measurements can be selected.
(3) The ventral manubrial spine is a transverse ridge less thick than the
buttonlike prominence of other genera. (4) The pneumatic foramen is
very small, less than a millimeter wide. (5) In addition to these fea-
tures, which have been verified in the present series, the one available
Nesochen has a less prominent intermuscular line, especially posterior-
ly. Possibly all of the above features, and certainly 1, 2, and 5, can be
attributed to curtailed flight.
One character that allows the separation of Branta from Anser,
Chen, Philacte, and Nesochen is the shape of the ventral manubrial
spine. In Branta the spine is compressed into a vertically spatulate






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


process, whereas in the other four it is of the normal peglike shape.
Two specimens of Cygnopsis and one of Eulabeia are intermediate in
this respect.

ANATINAE
In the ducks the sternal basin is distinctively flattened. The reduced
posterior surface of the dorsal sulcal lip and the less prominent costal
margins eliminate the large concavity at the anterior end of the sternal
plate. Miller found this character the best means of distinguishing
Chloephaga, here considered in the Anatinae, from the true geese.
All the duck tribes cannot be separated by sternal characters alone,
but a number of sternal features aid in distinguishing some tribes or
parts of tribes. For those tribes that cannot be characterized by the
sternum alone, the various genera are discussed under the tribal units
of Delacour (1954, 1956, 1959). Similarities to genera in other tribes
are mentioned.
TRIBE TADORINI (SHELDRAKES). Within the Anatinae the sheldrakes are
most like the true geese in features of the sternum, particularly in the
rather prominent dorsal sulcal lip and the numerous pneumatic fora-
mina in the sternal basin. In addition to lacking a distinct concavity
beneath the dorsal sulcal lip, the sheldrakes may be separated from the
closely similar true geese as follows: (1) the costal facets number six
or less, except in the aberrant Cereopsis and Tachyeres (in geese a
minimum of seven is present). (2) The costal margin typically tapers
posteriorly. The sternum of sheldrakes is narrowest immediately ad-
jacent to the last costal process; whereas in geese the narrowest point,
which is sometimes difficult to establish, always lies anterior to at
least two costal processes. The difference is undoubtedly a manifesta-
tion of the above characteristics.
Miller uses the shape of the sterno-coracoidal process to aid in
separating Chloephaga from the true geese; in Chloephaga it is longer
and projects more anteriorly. Although the process is variable, the
differences between Chloephaga and true geese are generally those be-
tween Anatinae and Anserinae, and therefore it serves to separate the
two subfamilies. Miller's other criterion for separating Chloephaga
from the true geese is the relative length of the posterior lateral pro-
cesses, extending well beyond the xiphisternum. As a few goose speci-
mens show the same feature, this character is not infallible.
The sheldrakes form a fairly distinct tribe. The sternal basin is
deeper than in other ducks, although there is overlap with some dab-
blers and perchers. The shape of the pneumatic fossa is also of limited


39







BULLETIN FLORIDA STATE MUSEUM


use. The fossa is typically a large opening bordered laterally by stout
bars, which frequently are fused with the sternal plate. The resulting
fossa does not have the round or eliptical shape of other ducks, but
instead it is a constricted opening that is either oval or somewhat rec-
tangular in outline. The sterno-coracoidal process is shorter and has
a more prominent posterior extension in the sheldrakes than in other
ducks.
Tachyeres differs strongly from other sheldrakes in its broad, flat
sternum. (1) The width is 55.6 percent of the basin length. (2) The
ventral manubrial spine barely protudes beyond the ventral sulcal lip.
(3) The carina is greatly reduced, with the posterior two-thirds of its
margin virtually a straight line. (4) The posterior lateral process curves
media more than in other sheldrakes. (5) The pneumatic fossa is ellip-
tical and small. (6) The sterno-coracoidal process is longer and lacks
a prominent posterior extension. The very shallow basin, ducklike
sterno-coracoidal process, possibly the elliptical fossa, and the seven
costal processes suggest that Tachyeres may be incorrectly located in
the sheldrake tribe.
Characteristics of the sternum of Cereopsis disclose little more than
the fact that it is aberrant. The element has qualities of both the shel-
drakes and the true geese. The following features were noted: (1)
The sternal basin is deeper than in sheldrakes, but lacks the concavity
beneath the dorsal sulcal lip found in geese. (2) The dorsal manubrial
area is notched as in many sheldrakes, whereas no geese have a distinct
notch. (3) The ventral manubrial spine is lacking. All geese have such a
spine, as do most sheldrakes. (4) The xiphisternum is not flared pos-
teriorly as is true of all sheldrakes and most geese. (5) The costal
processes number 6 or 7; a minimum of 7 was counted for geese, a
maximum of 6 for sheldrakes, Tachyeres excluded. (6) The carinal
margin is more curved throughout its length than in members of
either of the two tribes.
Among the more typical sheldrakes, Chloephaga has the widest
sternum (46.9 to 50.8 percent of basin length), Tadorna and Casarca
the narrowest (40.1 to 45.1 percent), whereas Alopochen (44.9 to 49.8)
and Neochen (45.3 to 45.8) are intermediate. Chloephaga usually has
abundant pneumatic foramina; Tadorna and Casarca have only the
large, centrally located one; Alopochen and Neochen are intermediate,
but nearer Chloephaga. In Chloephaga, Alopochen and Neochen the
posterior lateral processes extend well beyond the xiphisternum. In
Tadorna and Casarca, where they are shorter, they normally extend
less than 5 mm. beyond.


40


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Chloephaga has a narrower xiphisternum (its least width divided
by the least width between costal margins, 31.3 to 44.8 percent) than
Alopochen (66.5 to 66.9), and Neochen (50.5 to 54.6), but in Tadorna
and Casarca the structure varies greatly in width with the different
species. Chloephaga has a higher carina than Alopochen, and it ex-
tends farther back on the sternal plate. Neochen, Tadorna, and Casarca
are more like Chloiphaga in this respect.

TRIBE ANATINI (DABBLING DUCKS). The sternum of dabbling ducks
shows the following characteristics: (1) The sternal basin is shallower
than in the sheldrakes. (2) The single pneumatic foramen is elliptical
or round. (3) The ventral manubrial spine is usually present and typi-
cally long, thin, and peglike. (4) The sternum is narrow (Anas, Chaule-
lasmus, Mareca, Spatula, 37.5 to 48.9 percent of total length; Callonetta,
43.3; Malacorhynchus, 44.4; Hymenolaimus, 44.5), narrower than in
most members of the four diving-duck tribes. Rhodonessa and Mer-
ganetta are exceptions. (5) The posterior lateral processes are straight-
er than in divers and only occasionally fused with the xiphisternum.
Within the tribe the sterna of all genera except Rhodonessa and
especially Merganetta are very similar. Callonetta has two weak fea-
tures that support generic status: (1) The costal processes number
six, whereas the vast majority of specimens of typical dabblers have
seven, although the range is from six to eight. (2) The ventral manu-
brial spine is thinner, with a weak dorsal area for the ligamental at-
tachment.
Malacorhynchus has the ventral manubrial spine large and strong
as in typical dabblers but differs in having six costal processes. Hy-
menolaimus is also very similar to the typical dabblers, surprising when
one considers its habits. It has the following differences: (1) The
costal processes number six. (2) The ventral manubrial spine is re-
duced to a weak projection. (3) The dorsal manubrial area has a
prominent notch. (4) The carina is slightly reduced with its ventral
edge only slightly curved.
Rhodonessa can be distinguished at once from the typical dabblers
by several good sternal features: (1) The sternum is wider (50.8 per-
cent of basin length). (2) The dorsal manubrial area is notched. (3)
The ventral manubrial spine is lacking. The one available specimen
(USNM 344802) lacks the spine as apparently did the one used by
Verheyen (1955). Though occurring also in certain perching ducks,
this feature is generally limited to the species with diving habits, but
Rhodonessa does not habitually dive (Delacour, 1956).


1961


41






BULLETIN FLORIDA STATE MUSEUM


In Merganetta the sternum has the following features: (1) It is
wide, 52.7 to 52.9 percent of the basin length. (2) The ventral manu-
brial spine is lacking. (3) The carina is greatly reduced, the margin
being straighter than in typical dabblers. (4) The posterior lateral
processes curve more media. (5) The sternal notches are reduced to
1/4 of the basin length (they measure approximately 1/ in other dabbling
ducks). (6) The dorsal manubrial area is deeply notched, and has two
prominent lateral projections. The sternum of Merganetta diverges
from those of typical dabblers to the extent that tribal status for the
species may be justified.
The sternum of Salvadorina was studied by Mayr (1931), who found
the element somewhat narrower than in Anas platyrhynchos, especially
caudally, and with the intermuscular line less clearly marked. In
sternal characteristics he concluded that Salvadorina is closer to Anas
platyrhynchos than to Aythya.
TRIBE CAIRININI (PERCHING DUCKS). As the sternum of perching ducks
does not differ significantly from that of the dabbling ducks, it is im-
possible to characterize the tribe as a whole on the basis of this ele-
ment. Within the tribe, Cairina, Aix, and Dendronessa have the ventral
manubrial spine greatly reduced, whereas in Amazonetta, Chenonetta,
Nettapus, and Cheniscus it is prominent. Pteronetta and Sarkidiornis
are intermediate in this respect.
Cairina has numerous pneumatic foramina beneath the dorsal sulcal
lip and costal margins, and along the midline of the basin. In other
perching ducks, with the exception of the aberrant Plectropterus, only
the large, anteriorly and centrally located foramen is present. Plectrop-
terus resembles the sheldrakes more closely than the perching ducks
in the structure of the sternum: (1) The sternal basin is deeper than
in all ducks except certain sheldrakes. (2) The pneumatic foramen is
bordered laterally with struts as described for the sheldrakes. (3) The
dorsal manubrial area is deeply notched and has the lateral processes
found in certain sheldrakes.
TRIBE AYTHYINI (POCHARDS). Sterna of the three genera of pochards
are easily separable; Metopiana is the least specialized, Aythya the
most specialized, and Netta is intermediate.
Metopiana has the following sternal characters: (1) The ventral
manubrial spine is present as a prominent, single, peglike process.
When compared with dabbling ducks the spine of Metopiana is shorter
and thinner. (2) The dorsal manubrial area is notched as in all po-
chards. This character separates the sternum of Metopiana from the
similar nondiving ducks. (3) The width is less (43.2 to 47.4 percent


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


of the basin length) than in all other pochards, and also it is less than
in Rhodonessa and Merganetta of the dabblers. (4) The pneumatic
foramen is large (4 mm. wide), as in typical dabblers; it is much smaller
in Aythya. (5) The posterior lateral processes are longer, thinner, and
straighter than in other pochards.
Netta, which is osteologically intermediate between Metopiana and
Aythya, has the following features: (1) The ventral manubrial spine is
lacking. (2) The width is intermediate (51.5 to 52.1 percent) between
Metopiana and Aythya. Only two of 71 specimens of Aythya had a
relative width less than 53.0 percent. (3) The pneumatic foramen is
large (3 mm. wide) as in Metopiana.
Aythya possesses the following sternal characteristics: (1) The
ventral manubrial spine is usually a short, two-pronged structure with
the prongs flaring laterally. The length of the prongs varies as does
the depth of the notch between them. This feature is the best means
of separating the sternum of Aythya from those of all other ducks. (2)
The relative width is greater (51.3 to 66.7 percent) than in other
pochards. (3) The pneumatic foramen is reduced (less than 3 mm.
wide) but almost always present. (4) The posterior lateral processes
are shorter and wider, and curve farther media than in Metopiana.

TRIBE SOMATERINI (EIDERS). The sternum of eiders is typical of diving
ducks. The element is wide (53.0 to 58.6 percent of the basin length),
the dorsal manubrial area is widely notched, and the posterior lateral
processes are wide and curve toward the midline. The sternum is
most like that of the scoters, from which it can be separated by: (1)
The posterior lateral processes are wider, and more in line with the
long axis of the element. (2) The notches are usually shallower. (3)
There is less curvature throughout the entire element. In Polysticta
a small ventral manubrial spine is present as noted by Shufeldt (1909),
possibly indicative of a relationship with Clangula. In Somateria and
Lampronetta the spine is a short, bilobed protuberance.

TRIBE MERGINI (SEA DUCKS). As with other elements, the sternum of
sea ducks exhibits great structural variation. Several sternal struc-
tures occur nowhere in the Anatidae except in certain members of
this tribe: The genera Bucephala, Lophodytes, Mergellus, and Mer-
gus are the only waterfowl that regularly have sternal fenestrae in-
stead of notches. These genera and Clangula are the only ducks
with a pronounced abdominal plate extending beyond the postpectoral
line.
Though Bucephala and the mergansers agree in the presence of
sternal fenestrae instead of notches, they can be separated by the dis-


43






BULLETIN FLORIDA STATE MUSEUM


tance the carina extends anteriorly beyond the dorsal sulcal lip. In
order to obtain a measurement, a straight edge was laid along the
midline, from the posterior margin over the dorsal sulcal lip, and a
perpendicular was extended from this line to the carinal apex. The
distance along the straight edge from the perpendicular to the dorsal
sulcal lip is considered the amount of carinal overlap. The results
are given as a percentage of the basin length. In Mergus the range
is 25.6 to 35.6 (average, 31.59); in Bucephala the range is 11.4 to 22.0
(average, 16.13). Mergellus (18.5) and Lophodytes (18.5 to 19.9,
average 19.39) are intermediate, but closer to Bucephala. Most tax-
onomists confronted with the sterna of Mergellus or Lophodytes
would probably place them with Bucephala and not Mergus.
The pneumatic fossa is of limited use in distinguishing the mer-
gansers from Bucephala. In Mergus the foramen is large, approxi-
mately 5 mm. wide. Some specimens lack openings for the foramen
into the carina as mentioned by Shufeldt (1909), but usually these
are present. In Bucephala the foramen is smaller, under 4 mm.
Sometimes it is only a slight depression and frequently lacks openings
into the carina. Lophodytes has a wide pit, usually without open-
ings into the carina, and the one specimen of Mergellus has a promin-
ent foramen.
The relative width of the sternum in Bucephala (50.5 to 56.1 per-
cent), Mergellus (52.3), Lophodytes (49.5 to 55.2), and Mergus (47.7
to 54.2) is of little use for identification. The basin length used to
figure the above percentages does not include the variable abdominal
plate. The postpectoral line is used as the point from which the mea-
surement is taken.
The sternum of Clangula is easily distinguished from that of all
other waterfowl by the combination of a large abdominal plate and
sternal notches. The plate is relatively larger than in Bucephala and
the mergansers. The ventral manubrial spine varies from a short peg-
like process to a small bifid protuberance. The relative width of the
sternum varies from 50.3 to 55.0 percent.
Histrionicus has a relatively wide sternum (59.3 percent) and a
bifid ventral manubrial spine.
A greater curvature throughout the entire element characterizes
the sternum of the scoters (Melanitta and Oidemia). There is no
fixed point from which to measure the curvature, but it can be seen
by comparing the ventral edge of the carina or the juncture of the
carina with the sternal plate. The sternal basin appears significantly
deep in the scoters, because of the curvature of the element and


44


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


the more abruptly rising dorsal sulcal lip. The posterior lateral pro-
cesses are thinner, and more flared laterally than in the eiders Fur-
thermore, the notches are usually deeper. The sternal width (48.8
to 55.9 percent of basin length) and the diameter of the pneumatic
fossa (less than 0.5 mm. to over 4 mm.) are poor taxonomic criteria.
Scoters possess either a very short, bifid ventral manubrial spine or
none at all. The dorsal sulcal area is broadly notched.
The sternum of the extinct Camptorhynchus is illustrated in ven-
tral and lateral views in Rowley (1877). The specimen from which
the drawing was made, including the coracoids and furculum, is still
extant and is the only one known (Humphrey and Butsch, 1958).
The sternum resembles that of the eiders in that the posterior lateral
processes are wide, and in line with the long axis of the element, and
it lacks the basin curvature possessed by scoters. However, the ster-
num appears less specialized than in the eiders, for the posterior
lateral processes approach the xiphisternum, as in Histrionicus.

TRIBE OXYURINI (STIFF-TAILED DUCKS). The sternum in the stiff-tailed
ducks has the following features: (1) The pneumatic foramen is
lacking or minute. (2) The ventral manubrial spine is present, and
points more dorsad than in other ducks (except in Biziura, which
lacks the spine). (3) The basin is very shallow.
Oxyura, one of the most specialized of the stiff-tails, has these
sternal characters: (1) The width varies from 59.5 to 68.4 percent
of the basin length. (2) The ventral manubrial spine is wide and bi-
furcate distally. (3) The sternum has shallow notches in 0. jamaicen-
sis (12 specimens), fenestrae in 0. vittata (1 specimen). (4) The
posterior lateral processes are short, wide, and flaring. (5) The xi-
phisternum is wide. (6) The costal processes number 7, or rarely 8.
The sternum of Nomonyx is much less specialized. (1) It is rela-
tively much narrower (48.0 to 54.1 percent) than in Oxyura. (2)
The ventral manubrial spine is long, thin, and peglike. (3) The
notches are deeper than in Oxyura. (4) The posterior lateral pro-
cesses are thinner and curve farther media. (5) The xiphisternum
is narrower than in Oxyura. (6) The costal processes number six.
(7) The carina is reduced, as is typical of the tribe.
The sternum of Heteronetta has the large, dorsally directed ven-
tral manubrial spine that characterizes the tribe, but otherwise is
much less specialized than those of other members: (1) It is rela-
tively narrower (43.9 percent) than in Oxyura and Nomonyx. (2)
The ventral manubrial spine is wide basally but becomes thin distally.


1961


45






BULLETIN FLORIDA STATE MUSEUM


(3) The notches are deeper than in Oxyura and Nomonyx. (4) The
posterior lateral processes are thin and straight. (5) The xiphister-
num is narrower than in Oxyura and Nomonyx. (6) The costal
processes number six, as in Nomonyx.
The aberrant sternum of Biziura has the following features: (1)
The dorsal and ventral manubrial areas are widely and deeply notch-
ed. (2) The carina is greatly reduced, the posterior 4/5 of the mar-
gin being virtually a straight line. (3) The carinal apex does not
extend beyond the sulcal lips. (4) The posterior lateral processes
flare and then curve media. (5) The sternal notches are shallow.
(6) Two 5-mm. foramina are present on either side of and adjacent
to the carina, approximately 1/3 the basin length from the posterior
end (only 1 specimen is available and this may not be a normal fea-
ture). (7) The width is apparently great, but only 41.4 percent of
the basin length, because of reduction in the area posterior to the
costal margin. (8) The costal processes number seven.

Coracoid

The coracoid is an important taxonomic element. The angles between
certain parts of the bone, as well as proportions and structural details,
are useful.

ANSERANATINAE
The coracoid of Anseranas is vastly different from those of all other
waterfowl: (1) A coracoidal foramen is present as a circular open-
ing in the large procoracoid. The fenestra not only pierces the bone
but opens into the shaft as well. (2) A pneumatic foramen is present
on the dorsal surface anterior to the sternal facet. (3) The dorsal
portion of the sternal facet has a prominent medial lip that is essential-
ly perpendicular to the shaft. (4) The sternocoracoidal process has
a prominent knoblike extension. (5) The surface of the triosseal
canal is inflated, rather than depressed as in most other waterfowl,
and lacks the pneumatic foramina found in geese and swans. (6)
The angle formed between the axis of the head, best seen in anterior
view, and the plane upon which the dorsal surface lies is 88 to 93
degrees. Swans are the only other waterfowl that have an angle great-
er than 87 degrees. (7) The head is wider, and (8) the neck is less
constricted than in other waterfowl. (9) Depth through the scapu-
lar facet at its narrowest point is 16.3 to 17.5 percent of the length


46


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


(measured from the head to the internal distal angle), greater than
in all other waterfowl except certain swans and geese.
ANSERINAE
Although no single character of the coracoid distinguishes the Anser-
inae from the Anatinae, a combination of features proves diagnostic:
(1) The angle between the axis of the head and the plane upon which
the dorsal surface lies is 79 to 93 degrees, greater than in most Ana-
tinae. (2) The angle between the sternal facet and the shaft is small,
with a range from 70 to 83 degrees (measured with one straight edge
touching the internal distal angle and the median portion of the head,












,4
~. *4'


J


aJ
:B


I {


FIGURE 4. Right coracoid, ventral view. Top row: Anseranas semipalmata,
Dendrocygna autumnalis, Cygnus melancoriphus, Branta canadensis, Cereopsis
n.hollandiae. Bottom row: Tadorna tadorna, Anas rubripes, Merganetta armata,
Aythya affinis, Clangula hyemalis, Oxyura jamaicensis.


"- 1


47






BULLETIN FLORIDA STATE MUSEUM


and the other lying along the posterior border of the element). (3)
The ventral lip of the sternal facet is wide and concave, with the ex-
ternal edge essentially perpendicular to the shaft. (4) The median
edge of the sternal facet is typically broad and blunt, partially a re-
sult of the wide lips to the sternal facet.

TRIBE DENDROCYGNINI (WHISTLING DUCKS). The coracoid of whistling
ducks resembles that of swans and geese in most characteristics, but
its slender shaft gives it a decidedly ducklike appearance. Dendrocyg-
na can be distinguished from the swans and geese by the following
coracoidal features: (1) The depth is 12.6 to 14.1 percent of the
length. A minimum of 15.0 is recorded for the swans and geese. (2)
The width is 8.3 to 10.3 percent of the length (measured at the nar-
rowest point posterior to the procoracoid with the caliper legs per-
pendicular to the plane of the dorsal surface). Its minimum width
is 12.4 percent in the swans and geese. (3) The pneumatic foramina
beneath the furcular facet are minute or absent. (4) The ventral
surface has a pronounced depression immediately anterior to the ster-
nal facet and medial to the intermuscular line. This character makes
the coracoid of Dendrocygna separable at a glance from that of any
other bird.

TRIBE ANSERINI (SWANS AND GEESE). Although the coracoids of
whistling ducks and swans and geese show basic similarities, these
tribes can be separated easily. Swans and geese have the following
coracoidal properties: (1) The depth is 15.0 to 22.1 percent of the
length. (2) The width varies from 12.4 to 16.4 percent. (3) The
pneumatic foramina beneath the furcular facet are large and numer-
ous.
The coracoid supports the distinction of two groups within the
Anserini, one being swans and Coscoroba, the other the geese, previ-
ously defined by other skeletal elements. The major difference be-
tween the two is in the form of the triosseal canal: (1) In swans the
triosseal canal has no deep depression between the procoracoid and
the brachial tuberosity. In geese the depression is deep. (2) In
swans pneumatic foramina are small and extend under the entire fur-
cular facet. In geese, where they are larger, the foramina are normal-
ly restricted to the area beneath the brachial tuberosity. (3) The
angle between the axis of the head and the plane of the dorsal surface
ranges from 83 to 93 degrees in swans. In geese the range is 80 to
85 degrees. (4)The depth through the scapular facet ranges from


48


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


16.4 to 22.1 percent of the length in swans. In geese the range is
15.0 to 17.6 percent.
Coscoroba resembles the swans in the size and location of pneu-
matic foramina and the depth through the scapular facet (18.2 per-
cent). It is intermediate between swans and geese in the depth of
the triosseal depression and the angle of the head (83 degrees).
From the swans, to which it seems more closely allied, Coscoroba
differs as follows: (1) The ventral edge of the shaft in internal view
is virtually straight, whereas it is curved toward the ventral promin-
ence of the head in swans. (2) The sternal facet in posterior view
is straighter, less arched, than in swans. (3) The width below the
procoracoid is 13.7 percent of the length; swans range from 13.6 to
16.4, but only three of 36 specimens are narrower than Coscoroba.
Four coracoidal features that aid in separating Olor from Cygnus
are listed by Howard (1946): (1) The furcular facet is undercut for
its full extent in Olor. In Cygnus the facet is flattened against the
shaft ventrally with only a slight undercut near the brachial tuberos-
ity. Chenopis resembles Cygnus in this respect, although 1 of 4 spec-
imens is intermediate. (2) The procoracoid is larger in Olor and
smaller in Cygnus and Chenopis. (3) The coracoidal notch is absent
in Olor, although Howard notes some exceptions. In Cygnus there is
a more (C. olor) or less (C. melancoriphus) distinct notch located
where the coracoidal fenestra occurs. Two of four specimens of
Chenopis have the notch sealed off as an elongate fenestra. This
opening does not appear to be homologous with the foramen in the
procoracoid of Anseranas. (4) The scapular facet is broad and shal-
low in Olor. In Cygnus olor and Chenopis the area is more evenly
rounded. Cygnus melancoriphus is intermediate.
The coracoid exhibits a feature that allows for a separation of the
geese. Miller (1937) uses it to separate Branta from Anser and Chen,
but with the present series it has wider application. In Branta and
Nesochen the furcular facet is undercut for its full extent. In Anser,
Chen, Cyanopsis, Philacte, and Eulabeia the furcular facet is deeply
undercut dorsally, flattened against the shaft in the middle, and only
slightly excavated ventrally. Pneumatic foramina frequently occur
under the ventral portion of the facet in Branta and Nesochen, but
are absent in this area in the other genera.
Nesochen differs from other geese as follows: (1) The depression
in the triosseal canal between the procoracoid and the brachial tuber-
osity is shallower. (2) The angle of the coraco-humeral surface is


1961


49






BULLETIN FLORIDA STATE MUSEUM


more nearly transverse to the shaft. Miller also mentions that pneu-
matic foramina beneath the brachial tuberosity are greatly reduced,
but this is not the case with my one specimen.

ANATINAE
The following features when compared with those listed for the An-
serinae should identify coracoids of the many members of the Ana-
tinae: (1) The angle between the axis of the head and the plane of
the dorsal surface varies from 61 to 81 degrees, except in Cereopsis
and Plectropterus. (2) The angle between the sternal facet and the
shaft varies from 80 to 96 degrees, except in the gooselike sheldrakes.
(3) The ventral lip of the sternal facet is less prominent and slopes
sharply toward the shaft. Certain sheldrakes are exceptions. (4)
The flattened sternal facet has the ventral lip projecting medially;
thus, the median edge is pointed. Again certain sheldrakes are ex-
ceptions. (5) The prominent depression on the ventral surface in
Dendrocygna is lacking. (6) The depth through the scapular facet
(10.1 to 14.6 percent of the total length) is usually less than in swans
and geese. Cereopsis and Plectropterus are the exceptions.
When studying duck coracoids, difficulty arises from the extensive
individual variation exhibited by such features as the depth of the
depression in the triosseal canal, the length of the procoracoid, and
the length of the sterno-coracoidal process. Although other features
of the element are rather useful, it is not possible to characterize all
of the tribes as defined by Delacour (1954, 1956, 1959). Realloca-
tion of certain genera discussed below alleviates much of the diffi-
culty.
TRIBE TADORNINI (SHELDRAKES). Compared with those of other Ana-
tinae, the typical sheldrake coracoids have the following properties:
(1) The procoracoid averages larger than in other ducks. (2) The
triosseal depression averages deeper. (3) The surface of the furcular
facet has a depression ventral to the brachial tuberosity. (4) The furcu-
lar facet is undercut extensively near the brachial tuberosity. (5) The
angle between the sternal facet and the shaft is smaller, 75.5 to 81
degrees, the range for other ducks being 79 to 96 degrees.
Chloephaga, Neochen, and Alopochen are all rather similar and
agree in the following criteria: (1) The depression in the furcular
facet joins the undercut of the brachial tuberosity to form a notch in
the facet. (2) Pneumatic foramina are usually prominent beneath the
brachial tuberosity. The shape of the anterior end of the coracoid


Vol. 6





WOOLFENDEN: OSTEOLOGY OF WATERFOWL


differentiates these three genera. Alopochen has the deepest triosseal
depression. Neochen has the widest furcular notch, which occupies
most of the facet, and it also has the most prominent ventral tuber-
osity on the head. Chloiphaga has the shallowest triosseal canal,
essentially lacking in some specimens, and the largest lateral protub-
erance on the head, located at the termination of the coraco-humeral
surface.
Tadorna and Casarca can be characterized by the following fea-
tures: (1) The furcular facet is entire because the depression and
undercutting are less than in the three genera previously discussed.
(2) Pneumatic foramina are minute or lacking under the furcular
facet. The genus Casarca cannot be distinguished from Tadorna by
coracoidal features.
Cereopsis is an exception in all five properties of the coracoid that
aid in separating the Anserinae from the Anatinae, and the genus is
easily separated from the typical members of the sheldrake tribe:
(1) The angle between the axis of the head and the plane upon
which the dorsal surface lies is 83 to 85 degrees. A maximum of 81
degrees is found in the true sheldrakes. (2) The depth through the
scapular facet varies from 16.6 to 18.5 percent of the length. The
other genera range from 12.9 to 14.5 percent. (3) The width poster-
ior to the procoracoid varies from 14.0 to 15.8 percent of the length;
true members of the tribe vary from 11.0 to 12.8. (4) The furcular
facet is undercut for its full extent. In the others the facet is under-
cut only dorsally. (5) Pneumatic foramina are present under the
entire length of the furcular facet. In the true sheldrakes they are
either absent, or present only under the brachial tuberosity.
The coracoid of Cereopsis shows much greater resemblance to
that of the swans and true geese. From the swans Cereopsis differs
in having the head of the coracoid wider and shallower. It differs
from the geese in having the depression in the triosseal canal between
the procoracoid and the brachial tuberosity reduced.
Tachyeres can be distinguished from the typical sheldrakes as fol-
lows: (1) The angle between the axis of the head and the plane of
the dorsal surface is 71 degrees. In the remaining sheldrakes the
range is 72 to 81 degrees. (2) The depth through the scapular facet
is 11.0 percent of the length. The range for the typical sheldrakes is
12.0 to 14.5 percent. (3) The width posterior to the procoracoid is
10.6 percent. The range for the true sheldrakes is 11.0 to 12.8 per-
cent. (4) The angle between the sternal facet and the shaft is 87


1961


51






BULLETIN FLORIDA STATE MUSEUM


degrees. (5) The internal end of the sternal facet is elongated and
pointed. In the other genera assigned to the tribe the area is short
and blunt. (6) The dorsal and ventral lips of the sternal facet are
essentially flush with the shaft, whereas in sheldrakes they are prom-
inent. All of these features of Tachyeres indicate a relationship to
other Anatinae than the sheldrakes.

TRIBE ANATINI (DABBLING DUCKS). The one feature that seems char-
acteristic of the coracoid of the dabbling ducks is the angle between
the axis of the head and the plane of the dorsal surface. This varies
from 61 to 71 degrees. Exceptions are found in Merganetta and
Rhodonessa, the two genera that also differ significantly from the typi-
cal members of the tribe in other properties.
Merganetta can be distinguished by two features: (1) The angle
between the axis of the head and the plane of the dorsal surface is 74
degrees. (2) The head is deflected ventrally in medial view.
Rhodonessa resembles the pochards in the form of the coracoid.
It differs from the dabblers in the following ways. (1) The angle
between the axis of the head and the plane of the dorsal surface is
72.5 degrees, above the maximum recorded for the typical dabblers
but within the range of Aythya (72 to 75 degrees). (2) The head is
similar to that of the pochards (see description under pochard tribe).
The coracoids of the remaining genera of dabbling ducks show no
qualitative distinguishing features.

TRIBE CAIRININI (PERCHING DUCKS). The coracoids of perching ducks
are so similar to those of the dabblers, the two tribes cannot be dif-
ferentiated on the basis of this element. The one coracoid trend that
occurs in most species assigned to the perching ducks is the thicken-
ing of the head. The enlarged ventrolateral portion, upon which the
coraco-humeral groove terminates, gives the head an over-all robust ap-
pearance. The genera assigned to the tribe by Delacour (1959) fall
into four groups. The largest group contains Cairina, Aix, Dendron-
essa, Pteronetta, and Amazonetta. Another contains Chenonetta, Net-
tapus, and Cheniscus. The other two, very different from each other,
consist of one genus each, Sarkidiornis and Plectropterus. The uni-
fying features of the first of these units are associated with the cora-
coidal head: (1) The anterior end is rather pointed. (2) The ven-
tral prominence is deflected medially. (3) The furcular facet is in-
cised by a conspicuous groove.


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Cairina seems the most specialized of the group, and can be dis-
tinguished from the others as follows: (1) The groove in the furcu-
lar facet is very deep, notching the edge of the facet. (2) Pneumatic
foramina are prominent and often large. (3) The depth of the shaft
is 13.8 to 14.6 percent of the length. The maximum for the other
genera in the group is 12.8 percent.
Aix and Dendronessa have frequently been classified as dabbling
ducks, but their coracoids show a strong resemblance to that of Cairina.
The critical features are those listed above associated with its head. An
additional criterion is the less-curved median edge of the shaft in these
three genera.
Dendronessa cannot be separated from Aix, but the two together
differ from the other three genera in the group as follows: (1) The
depth (12.0 to 12.7 percent of the length) is greater than in Amazonetta
(11.8 percent) but less than in Pteronetta (12.1 percent) and Cairina.
(2) The groove in the furcular facet is generally deeper than in Amazo-
netta and Pteronetta, but not nearly as pronounced as in Cairina.
Pteronetta is very different from Cairina and similar to Anas in
the form of the coracoid: (1) The head is wider and less pointed.
(2) The groove in the furcular facet is wide and shallow. The ven-
trolateral portion of the head is enlarged, however, and shows its
affinities to the perching ducks. The coracoid of Amazonetta is inter-
mediate between those of certain dabbling ducks, namely Anas dis-
cors and A. cyanoptera, and of perching ducks such as Aix and Den-
dronessa, but the head seems more pointed than in Anas.
The second group, formed by Chenonetta, Nettapus, and Cheniscus
agrees in most characters with the preceding group, but lacks the
groove in the furcular facet. No coracoidal features distinguish
Cheniscus from Nettapus, but both differ from Chenonetta as follows:
(1) The depth is 10.7 to 12.9 percent of the length, whereas in Chen-
onetta it is 13.0 to 13.4 percent. (2) The ventral prominence of the
head is directed medially. In Chenonetta the prominence is directed
ventrally.
In Sarkidiornis and Plectropterus the depression in the triosseal
canal is extremely deep. Sarkidiornis differs from Plectropterus in
having the triosseal canal only 16.7 percent of the length, and the
ventromedial lip of the sternal facet very short, the shortest of any
waterfowl seen.
The Plectropterus coracoid differs markedly from those of other
perching ducks: (1) The triosseal canal is 19.7 to 21.0 percent of the


53






BULLETIN FLORIDA STATE MUSEUM


length. The range for other perching ducks is 13.4 to 18.5. (2) The
coracoidal head is wide and not pointed in medial view. (3) The
ventrolateral portion of the coracoidal head is not enlarged, and (4)
the neck is prominent.

TRIBE AYTHYINI (POCHARDS). Their coracoids show the pochards
form a distinct tribe readily separable from the others, both diving
and nondiving. Those of certain genera indicate the derivation of the
tribe was from the dabblers. The unique features of the tribe are
associated with the head: (1) Its ventral portion is reduced. In
medial view, the coracoidal head meets the ventromedial edge of the
shaft by a straight or gently curved line. (2) The bicipital attach-
ment is a thin groove instead of an elliptical facet. (3) The furcular
facet extends farther posteriad along the shaft. As mentioned in the
section on the dabbling ducks, Rhodonessa agrees entirely with all
these pochard characteristics.
Aythya has the most specialized coracoid of the pochards, where-
as Metopiana and Netta are intermediate between Aythya and the dab-
blers in most features. As the following characteristics indicate,
Rhodonessa also seems to be one of the less specialized pochards.
(1) The relative width of the triosseal canal, given as a percentage
of the length, is as follows: Aythya 11.6-14.7; Metopiana 13.8-15.0;
Netta 14.6-15.1; Rhodonessa 14.8; Dabbling Ducks 14.3-17.9 percent.
(2) The angle between the axis of the head and the plane of the dor-
sal surface has the following variation in degrees: Aythya 72-75;
Metopiana 70-72; Netta 69-71; Rhodonessa 72.5; Dabbling Ducks 61-
71 degrees. (3) The angle between the sternal facet and the internal
edge of the element measures: Aythya 86.5-91; Metopiana 85-87; Netta
87-88; Rhodonessa 86; Dabbling Ducks 82-86 degrees.
Aythya is best distinguished from Metopiana and Netta by the
depth of the element relative to its length. In Aythya the range is
from 10.9 to 12.6 percent; Metopiana (12.6 to 13.8), Netta (13.3 to
13.4), and also Rhodonessa (13.5) are relatively deeper.
Metopiana and Netta can also be separated by coracoidal features:
(1) The width is 10.0 to 10.6 percent of the length in Metopiana, 11.9
to 12.3 percent in Netta. (2) The sternal facet is 38.1 to 40.4 percent
of the length in Metopiana, 44.5 to 44.6 in Netta. The relatively short
length of the sternal facet in Metopiana is correlative to the presence
of a ventral manubrial spine on the sternum. (3) The ventromedial
edge of the head is straighter and more prominent in Netta.


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TRIBE SOMATERIINI (EIDERS). The eiders are considered an offshoot of
the dabbling ducks by Delacour (1956), and Humphrey (1958a), but
the coracoid has striking similarities with that of the scoters: (1)
The procoracoid flares dorsally and has the base enlarged in both
groups. (2) The triosseal canal is wide, 17.1 to 19.9 percent of the
length in eiders, 15.3 to 18.7 percent in scoters. (3) The sternal facet
is 43.3 to 47.1 percent of the length in eiders, 42.9 to 49.9 percent in
scoters. (4) The head has a large ventral prominence in both groups.
The characters that separate the coracoid of eiders from those of
scoters and the other sea ducks are less obvious. (1) The sternal facet
has the ventromedial lip essentially flush with the shaft. In scoters the
the lip departs abruptly from the shaft. (2) The sternal facet, at the
internal distal angle, is elongated and pointed. In the scoters this re-
gion is relatively blunt. (3) The angle between the axis of the head
and the plane of the dorsal surface is 70 to 81 degrees. In scoters the
range is 77 to 87 degrees. (4) The ventromedial edge of the shaft is a
sharp ridge and the surface from the ridge through the triosseal canal
is almost flat (a slight depression in many specimens). In scoters the
ridge is wider and it then curves abruptly toward the canal that normal-
ly houses a rather deep depression. (5) The ventral prominence of the
head is situated farther posteriorly than the brachial tuberosity. In
scoters the ventral prominence extends no farther back along the shaft
than the tuberosity, and frequently it is more anterior than the latter.
The one available specimen of Lampronetta shows no qualitative
features of the coracoid useful in distinguishing it from Somateria.
Polysticta is distinct from Somateria and Lampronetta, and certain of
its coracoidal features indicate an affinity to Histrionicus and Clan-
gula: (1) The axis of the head is 81 degrees from the plane of the dor-
sal surface. The range for other eiders is 70 to 79 degrees. (2) The
furcular facet is rounded. In other eiders the facet is flat and usually
has a depression ventral to the brachial tuberosity. The furcular por-
tion of the head in Histrionicus is similarly rounded.

TRIBE MERGINI (SEA DUCKS). The sea ducks exhibit considerable vari-
ation in the conformation of the coracoid, as in their other bony
elements. Somewhat useful in defining the tribe is the procoracoid,
which tends to flare dorsally with its base extending farther back on
the shaft. The eiders share this feature. The tribe may be divided into
two distinct groups on the basis of the element. One group contains
Bucephala and the merganser genera Lophodytes, Mergellus, and


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Mergus; the other contains Clangula, Histrionicus and the scoters,
Melanitta, and Oidemia.
The following characters of the coracoid distinguish these two
groups: (1) In Bucephala and the mergansers the sternal facet varies
from 33.2 to 39.7 (42.2 in 1 of 35 specimens) percent of the length.
In the others the range is 42.1 to 49.9 (39.6 in 1 of 17 specimens).
(2) In Bucephala and mergansers the sterno-coracoidal process is less
produced laterally and forms an angle of less than 45 degrees with the
shaft. In the others the process is produced farther laterad to form an
angle of more than 45 degrees with the shaft. (3) In Bucephala and
mergansers the triosseal canal varies from 11.1 to 15.4 percent of the
length of the bone. The range for the other four genera is 15.3 to 18.7.
(4) In Bucephala and mergansers the angle between the axis of the
head and the plane of the dorsal surface varies from 69 to 74 degrees,
whereas in the others the range is 72 to 87 degrees. (5) In Bucephala
and mergansers the furcular facet is frequently interrupted by a medi-
an depression. In the others the facet is usually distinct throughout
its length. Histrionicus is an exception. (6) In Bucephala and mer-
gansers the ventromedial edge of the shaft remains a sharp ridge to its
termination at the furcular facet. In the others the anterior end
broadens and underlies much of the furcular facet. Histrionicus is in-
termediate in this respect also. (7) The size of the ventral promin-
ence of the head presents a sequence in which the mergansers, and
particularly Lophodytes, have the smallest protuberance, Bucephala is
intermediate, whereas Histrionicus, Clangula, and the scoters have the
largest. The most natural break again seems to fall in the accustomed
place, between Bucephala and mergansers and the other sea ducks.
The mergansers are distinct from Bucephala and the other sea
ducks in only one inconstant feature of the coracoid, namely that the
ventral lip of the sternal facet in posterior view is prominent as a
broad curve to the internal distal angle. In other sea ducks the lip
shows a distinct concavity as it approaches the angle; beyond the
angle the lip is no longer prominent. Of 10 specimens of Bucephala,
2 could not be identified by this character, and 1 specimen of Melan-
itta is aberrant.
The length of the sternal facet relative to the length of the cora-
coid is useful in separating Bucephala (37.2 to 42.1) from Mergus
(33.2 to 37.2, one 39.7). However, when Mergellus (37.2) and Lo-
phodytes (34.8 to 38.6) are considered the character becomes less
definitive.


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Paleontologists have no difficulty in separating Lophodytes from
Mergus on the basis of size. Qualitatively the coracoids of the two
genera are very similar, but they show consistent differences in the
configuration of the glenoid facet: In Mergus the ventral rim of the
glenoid facet is rather angular with the anteroventral leg somewhat
rounded, the posterior leg essentially straight. In Lophodytes the an-
teroventral portion of the rim is broadly rounded, the posterior part
concave. The glenoid facet of Mergellus, while not as rounded at
the anterior end as in Lophodytes, shows its greatest resemblance to
that of this genus.
The four available specimens of Mergus merganser have deeper
triosseal depressions than the 17 of M. serrator.
The fossil duck Bucephala ossivalis Brodkorb (1955) from the
Bone Valley formation, usually referred to the lower Pliocene, is known
from the anterior half of a coracoid. The bone is very similar to that
of B. clangula and B. albeola, particularly in the shape of the furcular
facet and ventral prominence of the head. Perhaps the similarity of
certain features to those of the mergansers Mergellus and Mergus is
of phylogenetic significance. These features are the shallower head
(i.e., less pronounced ventrolateral prominence), more curved coraco-
humeral groove, and the general appearance of the glenoid facet.
In the second group of sea ducks Clangula has the most distinct
coracoid: (1) The depth through the scapular facet varies from 12.3
to 13.1 percent of length. The range obtained for Histrionicus and
the scoters is 13.2 to 14.3 percent. (2) The axis of the head has a smaller
angle to the plane of the dorsal surface (71 to 79 degrees); in the
scoters the range is 77 to 87 degrees, and in Histrionicus 78 degrees
was recorded. (3) The sternal facet varies from 39.6 to 43.4 percent
of the length, whereas in the others it ranges from 42.9 to 49.9. (4)
The furcular facet has a triangular appearance, the smallest angle be-
ing at the ventral prominence. In the other three genera the facet
presents a more ovoid shape.
Histrionicus is characterized by the following features: (1) The
depression in the triosseal canal is very deep in the one available speci-
men. (2) The ventromedial edge of the shaft is thin. In Oidemia,
where the triosseal depression is usually deep, the edge is relatively
wide, and constitutes about half of the shaft depth, measured between
the procoracoid and the head. (3) The head has a less protruding
ventral prominence, but the rounded furcular facet appears more tri-
angular than in the scoters. (4) The median portion of the ventral


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lip of the sternal facet is inconspicuous, extending only a short dis-
tance up the shaft.
Three features in Oidemia aid in its separation from Melanitta:
(1) The sternal facet varies from 46.6 to 49.9 percent of length.
Melanitta varies from 42.9 to 44.9 percent. (2) The depression in the
triosseal canal is deep. Although variable, it is not as deep as in
Melanitta. (3) The ventral prominence of the head is smaller and re-
sults in an almost circular furcular facet. In Melanitta, because of the
large ventral prominence of the head, the furcular facet is ovoid in
shape.

TRIBE OXYURINI (STIFF-TAILED DUCKS). The stiff-tailed ducks have a
fairly distinctive coracoid: (1) The ventral portion of the head extends
far down the shaft. (2) The brachial tuberosity is reduced. (3) The
sterno-coracoidal process is prominent. (4) The sternal facet, in pos-
terior view, is strongly arched throughout its length.
Heteronetta, the least specialized genus, has coracoidal features that
indicate a close affinity to the other members of the tribe, but it may
be distinguished as follows: (1) The depth through the scapular facet
is 11.8 percent of the length. Nomonyx and Oxyura range from 9.6 to
to 11.5 percent. (2) The axis of the head is 67 degrees from the plane
of the dorsal surface. In other members of the tribe the range is from
72 to 78 degrees. (3) The angle between the sternal facet and the
internal edge of the shaft is 84.5 degrees. In other stiff-tails the range
is from 86 to 96 degrees. In these three criteria Heteronetta is inter-
mediate between more specialized stiff-tailed ducks and the dabbling
ducks.
Nomonyx can be separated from other members of the tribe as fol-
lows: (1) The triosseal canal is narrow. The distance between the
undercut of the brachial tuberosity and the procoracoid constitutes
only 10.9 to 11.1 percent of the length. In others the range is from
12.0 to 16.6 percent. (2) The width of the shaft varies from 8.4 to 8.7
percent of the length. A range of 9.1 to 11.1 was obtained for other
stiff-tails. (3) The depth through the scapular facet, 10.8 to 11.5 per-
cent, is intermediate between Heteronetta (11.8) and Oxyura (9.6 to
11.0). (4) The brachial tuberosity is reduced. Nomonyx is closest to
Oxyura, but the numerous characters outlined above speak for its dis-
tinctness.
Oxyura is characterized as follows: (1) The relative depth is 9.6
to 11.0 percent. (2) The relative width is 9.1 to 10.7. (3) The angle


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


between the axis of the head and the plane of the dorsal surface is 72
to 75 degrees. (4) The angle between the sternal facet and the in-
ternal edge of the shaft is 87 to 96 degrees. (5) The triosseal canal
has a relative width from 12.0 to 15.2 percent. This last feature best
distinguishes Oxyura from Nomonyx, which has a narrow triosseal
canal.
Biziura has a unique coracoid, with the ventral portion of the head
larger and more ventrally directed than in any other anatid. In medial
view the entire area above the glenoid facet appears bent ventrally,
which makes the ventral portion of the head even more distinct. The
following features aid in characterizing the genus: (1) The depth
through the scapular facet is 12.2 percent of the length; a maximum
of 11.8 was obtained for the other genera. (2) The width of the shaft
is 11.1 percent of the length; a maximum of 10.7 was obtained for the
others. (3) The axis of the head is closer to perpendicular to the
plane of the dorsal surface (78 degrees) than in other genera (whose
maximum is 75 degrees). (4) The triosseal canal is 16.6 percent of
the length; 15.2 is the largest in the other stiff-tailed ducks.
Downs (1954) has studied the coracoid of several species of North
American ducks. He concludes that the degree of angulation of the
head is related to the method of taking flight. Those forms capable of
steep ascent (dabbling and perching ducks) have lesser angulation be-
tween the axis of the head and the plane of the dorsal surface, whereas
those which take off at a low incline (diving ducks) have greater an-
gulation. The data obtained from the present series of ducks support
Downs' theory. A range from 61 to 75 degrees was obtained from ex-
amples of the dabbling and perching ducks. The range for the species
assigned to the four tribes of diving ducks was 69 to 87 degrees, except
for Heteronetta (67 degrees).
The correlation between structure and function may have wider
application. The pied goose, whistling ducks, swans, and geese have
considerable angulation between the axis of the head and the plane of
the dorsal surface (79 to 93 degrees), and apparently they take flight
at a relatively low angle.
Scapula

The scapula has a few features of taxonomic importance. Howard
(1946) comments on the marked variability in the structural details of
the element in swans. Since only qualitative features are considered,
only a few genera and generic units can be characterized.






BULLETIN FLORIDA STATE MUSEUM


ANSERANATINAE
As with other elements, there are greater qualitative differences
between the scapula of Anseranas and those of other waterfowl
than exist between those of any other members of the group:
(1) The acromion is short, barely extending beyond the coracoidal ar-
ticulation. In other waterfowl the acromion is long and pointed. (2)
The triosseal ridge (a dorsally situated prominence of the acromion)
is a knoblike protuberance that extends over the anterior edge of the
acromion. (3) The blade is narrow and convex ventrally and the apex
is pointed. (4) A pneumatic fossa on the dorsal surface between the
glenoid facet and the acromion occurs in other waterfowl only in true
geese, Coscoroba, and Cereopsis.
ANSERINAE
The subfamily Anserinae cannot be characterized adequately by fea-
tures of the scapula.
TRIBE DENDROCYGINI (WHISTLING DUCKS). The scapula of whistling
ducks cannot be separated consistently from those of most of the Ana-
tinae. The one feature that seems fairly characteristic of Dendrocygna
is a narrow, pointed apex. The blade is also frequently narrow, al-
though in some specimens it is wide. That Anseranas also has a point-
ed apex and a narrow blade may be of phylogenetic significance.
TRIBE ANSERINI (SWANS AND GEESE). The occurrence of the pneumatic
fossa near the anterior end of the dorsal surface of the scapula is of
taxonomic significance within the swan and goose tribe. Swans lack
the fossa, whereas in Coscoroba and true geese it is present.
Three scapular features that aid in separating Olor from Cygnus are
listed by Howard (1946): (1) The muscular attachment on the ven-
tral surface of the acromion forms a short crest slightly back from the
internal border distally. In Cygnus the attachment follows the inter-
nal edge more closely. This character made possible the separation of
all but 4 or 5 of the 36 available swan specimens. (2) The acromion
is shorter and broader in Olor. This feature, which is best understood
by comparing the angle between the acromion and the shaft, is some-
what useful in distinguishing the two genera. In Cygnus, and particu-
lally in C. melancoriphus, the angle is more acute between the acrom-
ion and the shaft; and, therefore, the acromion appears longer and
more slender. (3) The shaft is thinner in Olor. This property does
not seem applicable to my series of swans. Chenopis resembles Cyg-
nus in all of the features discussed above.


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The scapula of Coscoroba differs from those of geese in the follow-
ing ways: (1) The pneumatic fossa is shallower. (2) The acromion
and its triosseal ridge are smaller. (3) The blade is wider.
Generic criteria are not present on the scapulae of geese. The only
comment Miller (1937) made for the five genera of true geese he
studied was that the scapula of Nesochen is proportionately smaller
and weaker. My one Nesochen agrees with these generalizations.

ANATINAE
It is not possible to separate any of the closely related tribes of
Anatinae on the basis of the scapula, though some features aid
in distinguishing certain tribes or tribal groups. These features
are discussed below under the classification of Delacour (1954, 1956,
1959).
TRIBE TADORNINI (SHELDRAKES). Cereopsis differs from the sheldrakes
and resembles the true geese in that the scapula possesses a pneumatic
fossa. The genus can be separated from the true geese by the fol-
lowing additional scapular features: (1) The acromion is directed
more media, and consequently the surface posterior to the acromion,
including the genoid facet, is broad. (2) The anterior edge, between
the coracoidal articulation and the acromion, is thicker. (3) A pro-
tuberance is present on the dorsomedial edge of the neck. Cereopsis,
true geese, and most other waterfowl possess a dorsal protuberance
that lies in the midde of the shaft; but true geese lack the more anter-
ior and median prominence found in Cereopsis. (4) The glenoid facet
lies almost in the plane of the anterior portion of the shaft. In true
geese the anterior portion of the facet is typically inclined lateroven-
trally.
The remaining genera of sheldrakes have no outstanding qualita-
tive features to separate them from related groups of Anatinae, or
from each other.
TRIBE ANATINI (DABBLING DUCKS). A few minor differences between
the scapulae of dabbling ducks and of diving ducks of the pochard,
eider, and sea duck tribes are detectable when large series of the ele-
ment are studied: (1) The acromion is shorter with the ventral surface
flat in dabblers. In diving ducks of the tribes listed above the acrom-
ion is longer, and in ventral view it usually reveals a knoblike process.
As a result, the anterior edge of the bone between the acromion and
the glenoid facet is concave; in dabblers the edge is straighter. (2)
The proximal portion of the scapula is not rotated. In the divers, in-


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eluding the stiff-tailed ducks, the rotation is such that the internal
edge and the acromion appears depressed. (3) The blade is usually
broadest near the midpoint. In pochards, and particularly Aythya,
the blade is narrow and tapers near its apex. In the other diving
tribes the blade is wide throughout.
Three genera among the dabblers have scapular features that en-
able them to be distinguished from other members of the tribe: In
Hymenolaimus the acromion is almost parallel with the trend of the
blade, whereas in other dabbling ducks it is more flaring; the blade is
of uniform width and has a blunt apex. In Merganetta the triosseal
ridge is reduced, and the anterior edge of the element is thick and
forms almost a straight line; the blade is narrow but rather thick. In
Rhodonessa the blade is narrow and the proximal portion is rotated
as in the pochards, but the ventral surface of the acromion is flat instead
of knoblike. Thus another element can be added in which Rhodonessa
shows affinities with the pochards.
TRIBE CAIRININI (PERCHING DUCKS). In the perching ducks the shape
of the blade and the acromion of the scapula is, generally speaking,
more like that of the dabblers than the divers. Plectropterus differs
from other members of the tribe as follows: (1) The muscular line
of the dorsal surface extends from the prominence at the posterior end
of the neck to the internal edge. In other perching ducks the ridge
curves anterolaterally and meets the glenoid facet. (2) The acromion
is shorter and thicker.
The Cairina scapula is typified by the following characteristics:
(1) A wide depression is present on the dorsal surface between the
glenoid facet and the triosseal ridge. The depression may contain
small pneumatic foramina. (2) The blade is thick and rounded.
The Pteronetta scapula lacks the dorsal depression and thick blade
of Cairina, and is similar to that of Aix, Dendronessa, Amazonetta,
Cheniscus, and Nettapus, none of which is separable from the other.
Chenonetta possesses a wide, rounded acromion. In Sarkidiornis the
acromion appears to flare more than in other perchers.
TRIBE AYTHYINI (POCHARDS). The pochard scapulae are characterized
as follows: (1) The acromion is longer and with a knoblike ventral
surface. (2) The proximal portion of the element is rotated so that
the internal edge and acromion appear depressed. (3) The blade is
relatively thin throughout. Metopiana usually has the blade tapering
as in the dabblers, but the anterior end is rotated, and the ventral sur-
face of the acromion is knoblike as in Aythya. Netta has the acromion


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shorter than in other pochards, but it is still knoblike; the blade is
narrow and the anterior end is internally depressed.
TRIBE SOMATERIINI (EIDERS). The eiders have the anterior end of the
scapula rotated as in other divers, and the blade uniform in width and
rather wide as in the sea ducks. Lampronetta appears indistinguish-
able from Somateria in scapular characters. The Polysticta scapular
acromion follows the trend of the shaft more closely, which makes it
appear longer, and has a larger concave edge between it and the glenoid
facet.

TRIBE MERGINI (SEA DUCKS). The scapulae of sea ducks can fre-
quently be separated from those of other waterfowl except the eiders:
(1) The anterior end is rotated as previously described. (2) The
blade is uniform in width and rather wide with a blunt apex. Often
the blade bends abruptly near the posterior end. This should not be
confused with the tapering found in approximately the same place in
the dabblers. The various members of the tribe cannot be distinguish-
ed by qualitative features of the scapula.
TRIBE OXYURINI (STIFF-TAILED DUCKS). The four available genera of
stiff-tails form a rather distinct group as evidenced by the following
scapular features: (1) The acromion is directed more anteriorly than
in other ducks. (2) The blade is very uniform in width, fairly nar-
row, and often thick. (3) The glenoid facet is laterally compressed.
From the scapula, Nomonyx seems the least specialized of the stiff-
tails. The glenoid facet is only slightly compressed and affords
the best means of separating the genus from other members of the
tribe. The thin, anteriorly directed acromion and narrow but thick
shaft serve to separate Nomonyx from Aythya, which it resembles in
other scapular features.
Heteronetta is also not as extreme in specialization of the scapula
as are Oxyura, and Biziura, but it is closer to these genera than to
Nomonyx. In Heteronetta the glenoid facet is more compressed medi-
ally than in Nomonyx, and the acromion is shorter than in Oxyura and
Biziura. In Oxyura the internal edge of the acromion forms essential-
ly a straight line with the internal edge of the blade, the glenoid facet
is greatly compressed, and the blade is wider than in Nomonyx and
Heteronetta. The Biziura scapula is quite similar to that of Oxyura,
but can be separated by its thicker anterior end and more prominent
triosseal ridge; also the blade curves to form a shallow, elongate con-
cavity along the anterointernal edge.


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Furculum
Considerable individual variation and a lack of articulating surfaces
make the furculum a poor element taxonomically. As with all the
elements studied, however, some features are worthy of mention.

ANSERANATINAE
Even an element as poor taxonomically as the furculum shows Anser-
anas to be unique among the waterfowl: (1) The furcular process
is large and truncate. (2) Pneumatic foramina are present in the
crotch formed at the point of fusion of the two clavicles. (3) The
clavicles are compressed, and relatively straight in lateral view. (4)
The appearance in anterior view is V-shaped instead of U-shaped.
(5) The coracoidal tuberosity is small or lacking. The distinctive na-
ture of the furcular process and shape of the furculum in anterior as-
pect were noted by Miller (1919).

ANSERINAE
The Anserinae cannot be distinguished as a unit by features of the
furculum.

TRIBE DENDROCYGNINI (WHISTLING DUCKS). The furculum of whistling
ducks is nonpneumatic, with a small coracoidal tuberosity and rather
deeply curved clavicles. In most cases it is indistinguishable from
those of the Anatinae.

TRIBE ANSERINI (SWANS AND GEESE). Most genera in the swan and
goose tribe have the furculum pneumatic, with the foramina occurring
along the lateral surface of the clavicles. The clavicles tend to be
more compressed, and the coracoidal tuberosity smaller than in the
Anatinae.
The furcula of swans and geese can be separated in most cases.
Swans and Coscoroba have the following features: (1) An extended
depression occurs along the lateral surface of the clavicles. It is lack-
ing in some Cygnus melancoriphus. (2) Pneumatic foramina, one to
several, frequently large, are located in the depression.
Coscoroba differs from true swans in a number of ways: (1) The
symphysis is narrow and a furcular process is present. (2) The de-
pression on the lateral surface of the clavicles is restricted to the area
between the coracoidal and scapular tuberosities. (3) The ridge for
the attachment of the interclavicular membrane crosses the lateral


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surfaces of the clavicles directly from the coracoidal tuberosity. In
true swans the ridge runs a considerable distance along the anterolat-
eral surface before crossing over to the posteromedial side. (4) The
pneumatic foramina are small and scattered throughout the depression.
The following features separate Olor from Cygnus and Chenopis:
(1) The symphyseal area is extended posterodorsally to allow space
for passage of the trachea ventrally into the sternal carina. In other
waterfowl, with the possible exception of Anseranas, the trachea re-
mains dorsal to the furcular symphysis. In Cygnus and Chenopis the
symphyseal area is broad and smooth. (2) The clavicular depression
is longer, deeper, and with several large pneumatic foramina. In
Cygnus olor and Chenopis the depression is less well developed, and
in Cygnus melancoriphus it is virtually absent. The pneumatic fora-
mina, although typically large, usually number one or two, and in
Cygnus melancoriphus they are minute or absent. (3) The clavicles
are thinner and more pointed. In Cygnus and Chenopis they are much
thicker and have rather blunt scapular tuberosities.
Geese have no extended depression on the lateral surface of the
clavicle, and pneumatic foramina are either absent or, if present, re-
stricted to the area between the coracoidal and scapular tuberosities.
Within the geese, the occurrence of pneumatic foramina in the
furculum is of taxonomic significance. Branta and Neochen lack the
foramina, whereas they appear in Anser, Cygnopsis, Eulabeia, and
Philacte, and in Chen, except for 1 of 9 specimens of C. rossii. No
other criteria were noted for the geese, although Miller (1937) men-
tions that in Nesochen the furculum is smaller and the processes weak-
er than in the North American genera.

ANATINAE
Within the diverse subfamily Anatinae only a few genera or generic
groupings are recognizable from the furculum.

TRIBE TADORNINI (SHELDRAKES). In its furculum Cereopsis resembles
the geese more than the sheldrakes. Two features easily distinguish it
from the latter group: (1) Pneumatic foramina are present in the
slight depression along the lateral surface between the coracoidal and
scapular tuberosities. (2) The clavicles are compressed and appear
straighter in lateral view.
The typical sheldrakes appear intermediate between the Anserinae
and the remaining duck tribes in furcular characters. Sheldrakes have


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the coracoidal tuberosity poorly developed as in the geese, and the
clavicles are only slightly compressed as is typical of ducks. Separa-
tion of the sheldrake genera from each other is not possible by quali-
tative features of the furculum.

TRIBE ANATINI (DABBLING DUCKS). In dabbling ducks the furcular
process and coracoidal tuberosity are typically large, and the clavicles
are rather round in cross section. Exceptions are Rhodonessa, Hymen-
olaimus, and Merganetta, in which the furcular process is essentially
lacking. In the latter two genera the clavicles are weak, and the ele-
ment is broadly U-shaped.
TRIBE CAIRININI (PERCHING DUCKS). Plectropterus does not fit in well
with the other genera of perching ducks; its furculum differs in having
the coracoidal tuberosity reduced and the clavicles compressed. Both
of these are characteristics of the sheldrakes. Cairina frequently pos-
sesses a small pneumatic foramen in one or both clavicles below the
scapular tuberosity, but is otherwise typical of the tribe.
TRIBES AYTHYINI, SOMATERIINI, AND MERGINI POCHARDSS, EIDERS, AND
SEA DUCKS). Members of these three tribes have the furcular process
small or absent, except in the pochard Metopiana where it is rather
prominent. In Metopiana and in those individuals of the other species
where a trace of the furcular process occurs, it is typically notched.
The feature correlates with an expansion posteroventrally of the double
sterno-furcular ligament (see Appendix) with a consequent reduction
in the single median ligamentous membrane. Mergus shows greater
curvature throughout the length of the clavicles in lateral view, but
otherwise it is not markedly different from other sea ducks.
TRIBE OXYURINI (STIFF-TAILED DUCKS). The furculum of the stiff-
tailed ducks is somewhat characteristic in that the element is thin and
rather weak. Heteronetta, which Delacour (1959) places only pro-
visionally in the tribe, agrees in the reduction of the element. The
least reduced furculum occurs in Nomonyx. Typical of all divers, mem-
bers of this tribe lack a prominent furcular process.

Femur
The leg seems more susceptible to adaptive modifications than the
wing. The femur in ducks that dive, for example, shows great unifor-
mity even though other taxonomic criteria indicate many of the genera
are only distantly related.


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ANSERANATINAE
The long, slender femur of Anseranas has several unique properties:
(1) The posterior intermuscular line swings from above the internal
condyle to the external edge of the shaft, and thence continues to the
obturator ridge. In other waterfowl the line is confined to the medial
side of the shaft and fails to meet the obturator ridge. (2) The inter-
nal condyle is elongate and equal or subequal in distal extent to the
external condyle. In other anatids the internal condyle is flattened and
does not extend as far distally. (3) The rotular groove is narrow.
(4) The element is less contorted so that the head is directed more
posteriad than in other waterfowl. (5) The anterior surface of the
shaft is convex at a point 2/3 the distance from the proximal end.

ANSERINAE
One property of the femur tends to link the whistling ducks, swans,
and geese, and separate them as a group from the Anatinae. The ex-
ternal condyle has the anterior ridge elevated from the trend of the
shaft. In other waterfowl the anterior surface in this region tends to
form a straight or posterior-curving line.

TRIBE DENDROCYGNINI (WHISTLING DUCKS). The femur of whistling
ducks superficially resembles that of the nondiving Anatinae. The fe-
mur of Dendrocygna has a shaft convexity similar to that described for
Anseranas. In other waterfowl the shaft is curved in a similar direction
at this point, but the curve continues onto the condyles instead of
straightening out distally.
TRIBE ANSERINI (SWANS AND GEESE). Swans and geese have the
straightest femur of all waterfowl. In lateral view the long axis of the
shaft is virtually a straight line. The bone also tapers markedly from
the wide trochanteric end to the thinnest point, which lies immediate-
ly proximal to the condyles. Cygnus melancoriphus shows some curv-
ature. Swans and geese are very similar in the form of the femur.
One consistent criterion for separating the two is that the external and
fibular condyles flare laterally in swans; in geese they are directed
more posteriorly.
Coscoroba can be separated from other swans by characteristics of
the femur: (1) The head is shorter and the neck is less distinct. (2)
The trochanter, particularly at its anterior tip, extends proximally. The
proximal extent of the trochanter is obviously greater than that of the
head.


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Within the swans no feature of the femur is strong enough to sep-
arate Cygnus, Chenopis, or Olor completely, but the form of the neck
as seen in proximal view is helpful. Cygnus and Chenopis tend to
show a depression on the anterior surface between the trochanter and
the head. In Olor a low ridge extends from the trochanter toward the
head. Thus the neck appears more constricted in Cygnus and Chen-
opis than in Olor.
The shape of the femur is of little use in defining the genera of true
geese. Miller (1937) lists the following features that aid in the separ-
ation of Chen and Branta: (1) In Branta the medial crest bordering
the popliteal area is less deflected medially, and hence it is straighter
and more in line with the shaft. (2) In Chen the rotular groove is
narrower, and thus appears deeper. (3) In Chen the outer surfaces of
the condyles converge toward one another anteriorly, whereas in
Branta they are more nearly parallel. (4) In Chen the internal condyle
is narrower. In my series the first of these four features is the most
useful, but all are highly fallible and are further obscured by the ex-
treme similarity of the skeleton of Anser to that of Chen, as noted by
Miller (1937) and Howard (1946).
Nesochen differs from other geese, as noted by Miller (1937), in the
following ways: (1) The rotular groove is extremely broad. (2)
The neck is short and directed more posteriad, less media. Miller
also states that the femur of Philacte has the popliteal depression nar-
rowed by inflation of the lateral margin.
To the features listed above one more can be added. In Branta
and Nesochen the trochanter is extended slightly more proximad at its
anterior tip, and the posterior rim straightens instead of curving to-
ward the head. Chen, Anser, and Cygnopsis, in which the trochanter
has its most proximal extent in the middle and the posterior rim curves
toward the head, are usually separable by this feature. Eulabeia, and
to a lesser extent Philacte, resemble the latter group most in this re-
spect.

ANATINAE
The Anatinae show no significant elevation of the anterior edge of the
external condyle from the shaft as do the Anserinae. On femoral
characteristics the seven tribes of Anatinae are divisible into two
groups; one contains the nondiving tribes, the sheldrakes, dabbling
ducks, and perching ducks; the other the diving tribes, the pochards,


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eiders, sea ducks, and stiff-tailed ducks. The distinguishing features
are as follows: (1) The shaft is less curved in lateral and anterior
views in the nondivers. (2) The anterior ridge of the trochanter is
larger in the nondivers, and the shaft in lateral view curves an-
teriorly as it passes proximally to the anterior trochanteric prominence.
(3) The popliteal fossa is shallow in the nondivers. (4) The outer
surfaces of the condyles are nearer parallel, whereas in divers they di-
verge posteriorly. These differences cause the femur, when it is plac-
ed anterior surface down on a plane, to have the head elevated from
the plane in the nondiving tribes, whereas it lies on the plane in the
diving tribes. Merganetta of the dabblers and Metopiana of the poch-
ards are exceptions. Heteronetta appears intermediate because the
head is slightly elevated from the plane. In Tachyeres, although the
head is distinctly elevated, there are other features that cause it to re-
semble the diving assemblage.

TRIBE TADORNINI (SHELDRAKES). The following femoral characteristics
while not diagnostic, aid in separating the sheldrakes from the other
nondiving ducks: (1) The head is directed more proximally, less lat-
erally. (2) The trochanter in lateral view extends more anteriorly,
and in proximal view it curves more medially. In dabblers and perch-
ers the posterior portion of the trochanter tends to form an angle,
whereas in the sheldrakes it is a smooth curve.
Significant differences in the femur were not found among the shel-
drakes, except for the aberrant genera Cereopsis and Tachyeres. Cere-
opsis resembles the Anserinae in that the anterior ridge of the external
condyle is elevated from the shaft. The following additional features
serve to distinguish the genus: (1) The external and fibular condyles
and the fibular groove are directed medially at the distal end. Thus
the fibular condyle extends farther distally than the point of its junc-
tion with the external condyle. The opposite is the case in all other
waterfowl. (2) The shaft in anterior view is straighter, as described
for the true geese.
The femur of Tachyeres is unique. (1) A deep pit occurs on the
posterior surface medial to the obturator ridge and distal to the iliac
facet. (2) A depression is present in the rotular groove. The shaft
of the femur in Tachyeres is deeply curved and the popliteal fossa is
deep-adaptions for diving. Its femur also has a prominent anterior
ridge, and the condyles have the outer surface less divergent posterior-
ly-features of the nondiving ducks.


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TRIBES ANATINI AND CAIRININI (DABBLING AND PERCHING DUCKS). The
numerous genera of dabbling and perching ducks, with but few ex-
ceptions, cannot be distinguished on the basis of femoral characteris-
tics. Hymenolaimus and Merganetta, two diving members of the dab-
bling-duck tribe, have the popliteal fossa deep. Hymenolaimus, the
least specialized of the two, possesses the following additional fea-
tures: (1) The head is larger, and (2) the rotular groove is wider.
Merganetta resembles the divers more than the other dabblers in
the features listed to separate the two groups. It can be separated
from the diving tribes in the following ways: (1) The internal con-
dyle has the posterior end directed more media, a feature shared with
the pochards. (2) The trochanter in proximal view has its anterior por-
tion reduced more than in pochards. (3) The posterior intermuscular
line forms a more prominent ridge to the base of the head.
Although Rhodonessa is very similar to typical dabblers in the
shape of the femur, it is linked with the pochards by the first three
characteristics to be listed later for Metopiana. Plectropterus is sim-
ilar to the sheldrakes in the femoral features listed for that tribe.
TRIBE AYTHYINI (POCHARDS). The femur of pochards is readily told
from those of other diving ducks: (1) The trochanter in proximal
view extends farther anteriorly. (2) The head in proximal view is
smaller. (3) The medial side of the internal condyle is less flared
laterally.
Metopiana, as indicated by other taxonomic criteria, is a pochard.
The form of the femur indicates it is poorly specialized for diving. On
criteria used to differentiate the femora of diving and nondiving ducks
Metopiana resembles the nondivers, but it may be separated from non-
divers as follows: (1) In lateral view the anterior edge of the con-
dyles are more deflected. (2) The external and fibular condyles are
produced distally. (3) The internal condyle is enlarged and flares
medially to leave a distinct depression on the medial side of the shaft.
(4) The posterior surface of the shaft possesses a raised ridge to the
external condyle, and the portion of the shaft lateral to the ridge is
depressed. (5) The head is directed more proximad, less laterad.
Metopiana, of course, is separable from other pochards by the features
used to separate the nondivers from the divers.
Netta, although closer to Aythya than is Metopiana in the form of
the femur, also appears less specialized for diving than Aythya. The
popliteal fossa is shallower and narrower, and the anterior portion of
the trochanter is produced farther anteriorly.


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TRIBES SOMATERIINI AND MERGINI (EIDERS AND SEA DUCKS). The fem-
ora of the remaining diving ducks, the eiders, sea ducks and stiff-tailed
ducks, are very similar. A combination of the following features sep-
arates the more similar eiders and sea ducks from the stiff-tails: (1)
The anterior ridge of the internal condyle is approximately equal in
size to that of the external condyle. In stiff-tails the ridge of the ex-
ternal condyle is larger. (2) The fibular condyle is less flared lateral-
ly. (3) The pit for the tibialis anticus is more prominent than in the
stiff-tails.
TRIBE SOMATERIINI (EIDERS). The following features of the femur
tend to separate the eiders from the sea ducks: (1) The shaft in lat-
eral view is straighter. Although varying with the genera, in sea ducks
where the posterior curvature of the shaft is greater, when the anterior
surface of the femur is placed on a plane the internal condyle is eleva-
ted from the plane (Mergus is an exception). In eiders the internal
condyle typically touches the plane. (2) The anterior ridge of the in-
ternal condyle curves farther media as it extends distally. This fea-
ture is poorly developed in Polysticta. (3) The scar extending up the
lateral surface of the shaft from the fibular condyle is shorter.
Lampronetta cannot be distinguished from Somateria by femoral
characteristics, but Polysticta has several distinguishing features: (1)
The anterior portion of the trochanter possesses a more prominent
medially directed protuberance. (2) The fibular groove is narrower.
(3) The ligamental attachment, on the medial surface of the internal
condyle, is a more prominent projection. (4) The anterior ridge of
the internal condyle is straighter, not flared as far media.
TRIBE MERGINI (SEA DUCKS). The two groups of genera of sea ducks
established on the basis of other elements still hold with the femur,
but the differences are less apparent: (1) In Bucephala and the mer-
gansers the trochanter has more of the anterior edge inflected, and
thus the notch between it and the head is narrower. In the other
sea ducks more of the trochanter slopes away from the head as it
passes anteriorly, only the tip is inflected, and the notch is corre-
spondingly wider. (2) In Bucephala and the mergansers the fibular
condyle, particularly in anterior view, appears to flare more from the
shaft. This feature is especially good for separating Clangula and His-
trionicus from Bucephala, but it is poor for the scoters.
Generic characters are distinct within the Bucephala and mergan-
ser group. In Bucephala (1) the shaft has much greater posterior


1961


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BULLETIN FLORIDA STATE MUSEUM


curvature, and (2) it is thinner. The least width, given as a percen-
tage of the total length, varies from 7.1 to 8.0 percent. Mergellus
(7.5) also has a thin shaft, but Lophodytes (8.3 to 9.2) and Mergus
(7.9, 8.3 to 9.8) are much stouter.
In other femoral features Mergellus and Lophodytes are intermedi-
ate between Bucephala and Mergus. (1) The shaft is straighter,
without the abrupt bend found in Bucephala. (2) The shaft is nar-
row, without the marked lateral compression found in Mergus. The
least depth of the shaft, given as a percentage of the total length in
Mergellus and Lophodytes (9.5 to 10.7), overlaps Bucephala (8.0 to
9.9), but is narrower than Mergus (11.0 to 12.6). Mergellus differs
from Lophodytes in that the shaft is thinner and narrower. (1) The
shaft width is 7.5 percent of the total length compared with a range
from 8.3 to 9.2 percent on Lophodytes. (2) The shaft depth is 9.5
percent compared with a range from 9.8 to 10.7 percent in Lophodytes.
The characteristics that distinguish the straight, stout, compressed fem-
ur of Mergus from those of the other three genera are all mentioned
above.
The remaining four sea duck genera, Melanitta, Oidemia, Histri-
onicus, and Clangula, are very similar in the form of the femur. The
shape of the shaft, however, divides them into two groups. Melanitta
and Oidemia femora in lateral view show a most distinct posterior
curvature at the point 2/3 the distance down the shaft. In Histrioni-
cus and Clangula the shaft is much straighter. When femora of the
four genera are placed anterior surfaces down on a plane, the condyles
almost touch the plane in Histrionicus and Clangula, whereas in Me-
lanitta and Oidemia the condylar region is elevated more than 2 mm.
Only the relative shaft widths separate the remaining two pairs of
these genera; in Oidemia this varies from 8.2 to 8.5 percent of the total
length, whereas in Melanitta it ranges from 7.2 to 8.0 percent. In
Histribnicus it measures 8.6 percent; in Clangula 7.8 to 8.2 percent.
TRIBE OXYURINI (STIFF-TAILED DUCKS). Although other elements of
the stiff-tailed ducks are distinctive, only minor differences in the
femur separate them from the eiders and sea ducks.
Heteronetta, the least specialized of the four available genera of
stiff-tailed ducks, has the following femoral properties: (1) The an-
terior portion of the trochanter is enlarged. (2) The condyles have
the outer surfaces more nearly parallel. (3) The shaft is thin (6.9
percent of the total length); in the other three genera the range is 8.1
to 10.1 percent. (4) The head is small. (5) The ridge extending up


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the posterior surface of the shaft from the external condyle is reduced.
Nomonyx is also little specialized: (1) The anterior portion of the
trochanter is larger than in Oxyura and Biziura, but smaller than in
Heteronetta. (2) The internal condyle has the posterior portion direc-
ted more media. (3) The ridge extending up the posterior surface
of the shaft from the internal condyle is reduced. (4) The shaft in
lateral view is straighter, and lacks the distinct posterior flexure. In
characteristics of the femur, Nomonyx looks less like Oxyura than does
Biziura.
Biziura and Oxyura are highly specialized, but in different ways.
(1) In Biziura the shaft is thicker, 10.1 percent of the total length;
in Oxyura the range is 8.1 to 8.5 percent. (2) In Biziura the tro-
chanter extends proximally well beyond the head, and its distomedial
surface is swollen. (3) The posterior intermuscular line is indistinct,
but the lobe near the midpoint is more prominent in Biziura.

Tibiotarsus
The tibiotarsus is a useful taxonomic element for certain waterfowl, but
shows no distinguishing characteristics for others.

ANSERANATINAE
A few features, none of them striking, isolate the tibiotarsus of the
primitive pied goose, Anseranas: (1) The rim of the internal condyle
in medial view is more gently sloping and less extended posteriorly, and
lacks the notch present in other waterfowl. (2) The posterior portion of
the rim of the external condyle is gently sloping. (3) The posterior ends
of the rims of both condyles are elevated from the shaft more than in
other waterfowl. (4) The ligamental attachment is small. (5) The in-
ner cnemial crest is almost straight, with little lateral deflection.

ANSERINAE
It is impractical to attempt to define the whistling ducks, swans, and
geese as a unit with so poor a taxonomic element as the tibiotarsus.

TRIBE DENDROCYGNINI (WHISTLING DUCKS). A combination of the fol-
lowing features usually identifies Dendrocygna: (1) The condyles are
almost parallel; in other waterfowl they diverge more as they extend
anteriorly. (2) The external ligamental prominence is smaller. (3) The
external condyle is little produced anteriorly, and thus appears circular
in outline; in other waterfowl the outline is elliptical. (4) The fibular
crest is wide towards the distal end.


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TRIBE ANSERINI (SWANS AND GEESE). In swans and geese the lateral tip
of the outer cnemial crest lacks the distally directed hook characteristic
of other waterfowl. The two groups within the tribe can be separated
rather easily. In the swans and Coscoroba the intermuscular line flares
medially to reach the region of the ligamental attachment. In geese
the line is straight and fails to reach the ligamental attachment. This
feature possibly is correlated with the more terrestrial nature of the
geese.
In Branta and Nesochen the inner cnemial crest is straighter, where-
as in the other goose genera it is deflected towards the lateral side. A
longer fibular crest, detected by Miller (1937), is useful for distinguish-
ing Nesochen from the other geese.

ANATINAE
The Anatinae as a unit cannot be defined conveniently by characteris-
tics of the tibiotarsus. Study of the element for the genera within the
group indicates three primary sections: (1) sheldrakes; (2) dabbling
ducks, perching ducks, and pochards; (3) eiders, sea ducks, and stiff-
tailed ducks.
TRIBE TADORNINI (SHELDRAKES). The sheldrakes have the proximal
portion of the intermuscular line straight and removed from the anter-
omedial edge proximally, as in the true geese. In this way they differ
from the other Anatinae. Their terrestrial habitat is suggested as a
reason for this feature. Tachyeres is an exception; it resembles the
dabblers.
The most obvious break in the characteristics of the tibiotarsi of
the sheldrakes places Cereopsis, Chloephaga, and Neochen in one
group, and Alopochen, Tadorna, and Casarca in another. The differ-
ences pertain to the distal condylar region: (1) The condyles are in
line with the shaft in the first group, displaced medially in the other.
(2) In the first group the internal condyle is essentially equal in anterior
extent to the external condyle, in the second the internal condyle ex-
tends farther anteriorly.
The Cereopsis tibiotarsus has the hooked outer cnemial crest typi-
cal of the sheldrakes. It is intermediate between those of the shel-
drakes and the true geese in the position of the intermuscular line.
Perhaps of greatest significance are several unique features: (1) A
pronounced ridge extends from the outer cnemial crest onto the anter-
ior surface of the shaft, whose surface is convex; in other sheldrakes
the anterior surface is virtually flat. (2) The inner cnemial crest has litt-
le lateral flexure of the proximal tip. (3) The external articular surface


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has a much more prominent lobe, and the depression immediately
anterior to it is much deeper. (4) The shelf medial to the external ar-
ticular surface extends farther out over the posterior portion of the
shaft. (5) The supratendinal bridge tapers toward the medial side, and
its medial abutment is recessed from the medial ridge of the shaft. (6)
The tubercle for the oblique ligament, situated lateral to the supraten-
dinal bridge, is enlarged (Wetmore, 1943).
Chloephaga and Neochen resemble the other sheldrakes and differ
from Cereopsis in lacking the pronounced ridge on the anterior surface
of the tibiotarsus. Chloephaga and Neochen may be separated by the
relative width of the shaft. The width, which was taken with the cali-
per legs parallel to the condyles, is reduced to a percentage of the
length, which was taken with the exclusion of the cnemial crests.
Chlophaga varies from 4.9 to 5.2 percent; Neochen is 4.6 percent.
Alopochen forms a link between Chloephaga and Neochen and Ta-
dorna and Casarca. Alopochen differs from Chlopphaga and Neochen
in that the internal condyle has its posterodistal rim curving gently to
the shaft. In Chlo'phaga and Neochen the rim extends farther poster-
iorly and then curves abruptly to the shaft. Alopochen differs from
Tadorna and Casarca as follows: (1) The internal condyle has the an-
terior protuberance almost parallel to that of the external condyle. In
Tadorna and Casarca the internal condyle flares medially. (2) The
shaft possesses less medial curvature.
Tachyeres is distinguishable from other sheldrakes in that (1) the
intermuscular line follows the anteromedial edge as in ducks other than
sheldrakes; and (2) the condyles show greater medial deflection, with
the external condyle extending farther distally and the internal condyle
extending farther anteriorly, as in the section containing the dabbling
ducks. In Tachyeres the internal articular surface extends farther pos-
terolaterally than in other members of the dabbling-duck section. Cor-
respondingly the articular surface is supported by a raised ridge on the
shaft.
TRIBES ANATINI, CAIRININI, AND AYTHYINI (DABBLING DUCKS, PERCH-
ING DUCKS, AND POCHARDS). In dabblers, perchers, and pochards the
condyles of the tibiotarsus are displaced medially so that the external
condyle obviously extends farther distad than the internal condyle. In
addition the internal condyle tends to extend farther anteriorly than
the external condyle. Merganetta is not well defined by these features.
TRIBE ANATINI (DABBLING DUCKS). Chaulelasmus, Spatula, and Mareca
are not separable from Anas by qualitative features of the tibiotarsus,
nor is Callonetta. The other genera available in my series, Malaco-


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rhynchus, Rhodonessa, Hymenolaimus, and Merganetta, are distinctive.
Malacorhynchus is most similar to the typical dabblers. My single
specimen, which has the cnemial crests eroded away is distinguished
by the enlargement of the ligamental attachment.
Rhodonessa has the following properties of the tibiotarsus: (1) The
condyles are more in line with the shaft. (2) The internal condyle ex-
tends farther anteriorly, resembling Netta. (3) The inner cnemial crest
is directed more proximad, less anteriorly, as in pochards. Hymenolai-
mus has the outer cnemial crest extending farther proximad, with the
external edge directed more anteriorly, less laterad, and the shaft with
a more distinct curvature, the medial side being concave. Merganetta
has the greatest number of distinctive features: (1) The inner cnemial
crest is directed more proximad, less anteriorly. (2) The outer cnemial
crest has the laterodistal end directed more anteriorly, less laterad.
(3) The condyles are almost equal in distal extent.

TRIBE CAIRININI (PERCHING DUCKS). Diagnostic features of a qualita-
tive nature are not well developed in the tibiotarsus of perching ducks.
Apparent differences between certain genera usually break down in
series. Plectropterus is the most distinct genus assigned to the tribe;
the external condyle is almost in line with the external edge of the
shaft, a feature typical of the sheldrakes. Cairina has the condyles dis-
placed farther medially than in most other perchers, and the shaft is
robust, 5.9 to 6.7 percent of the length; the maximum in other genera
is 5.7 percent in Pteronetta.
TRIBE AYTHYINI (POCHARDS). The posterior intercondylar sulcus tends
to be wider in pochards than in dabbling and perching ducks, but no
additional features of the tibiotarsus are diagnostic of the tribe. With-
in the tribe, Metopiana has the following distinguishing characteristics:
(1) The outer cnemial crest is broader and directed farther laterad.
(2) The shaft is more robust; the width varies from 5.6 to 6.0 percent of
the length. In addition to these features, the shaft is markedly bowed,
the medial surface being concave, but my three specimens are all from
captive birds, in which bowing of certain elements including the tibio-
tarsus often occurs.
Netta and Aythya show closer resemblance to each other in the
tibiotarsus than either does to Metopiana. In both genera ,the outer
cnemial crest is narrower and directed more anteriorly, and the shaft
is thinner, the width being usually less than 5.0 percent of the length.
Netta can be distinguished from Aythya as follows: (1) The outer
cnemial crest lacks the prominent terminal apex and its medial portion


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is less deeply concave. (2) The inner cnemial crest is shorter. (3) The
condyles are more in line with the shaft, less deflected medially.

TRIBES SOMATERIINI, MERGINI, AND OXYURINI (EIDERS, SEA DUCKS, AND
STIFF-TAILED DUCKS). Three duck tribes, the eiders, sea ducks, and
stiff-tailed ducks, compose a group in which the condyles of the tibio-
tarsus are typically equal in distal and anterior extent. Heteronetta
and Nomonyx are exceptions and show certain resemblances to the
nondivers.

TRIBES SOMATERIINI AND MERGINI (EIDERS AND SEA DUCKS). Eiders and
sea ducks are similar and differ from the stiff-tailed ducks as follows:
(1) The internal condyle is less extended anteromedially. (2) The ex-
ternal ligamental prominence is small and does not extend as far laterad
from the external condyle.

TRIBE SOMATERIINI (EIDERS). The eiders differ fom the sea ducks and
also from the stiff-tailed ducks in the shape and direction of the outer
cnemial crest, which is wider and directed more laterad, less anteriorly.
Polysticta can be distinguished from Somateria and Lampronetta by
one qualitative feature of the tibiotarsus; in Polysticta the condyles lie
more nearly in line with the shaft. Lampronetta shows no significant
differences from Somateria, as has been the case with other elements;
in both the internal condyle is deflected farther medially.

TRIBE MERGINI (SEA DUCKS). The narrower, more posteriorly directed
outer cnemial crest separates sea-duck tibiotarsi from those of the
similar eiders. The usual break in the sea-duck genera is evident from
the tibiotarsus. In Bucephala, Lophodytes, Mergellus, and Mergus
the proximal edge of the outer cnemial crest is virtually a straight
diagonal line. In Melanitta, Oidemia, Histrionicus, and Clangula the
proximal rim of the outer cnemial crest is distinctly bent towards the
inner cnemial crest as it nears the juncture of the two.
Bucephala and the mergansers are very similar in the appearance of
the tibiotarsus. They differ slightly in additional details of the cnemial
crests. In Bucephala the inner cnemial crest appears narrower in medi-
al view and it extends proximally as a prominent peak. When the ele-
ment is placed with the posterior surface, including both condyles, ly-
ing on a plane, the external articular surface extends farther laterad
than the outer cnemial crest. In Mergus the inner cnemial crest is
wider, and at its juncture with the outer crest it bends anteriorly. In
the same view, in Mergus the outer cnemial crest usually extends far-
ther laterad than the external articular surface. Lophodytes and Mer-


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gellus are closer to Mergus in the width of the inner cnemial crest and
in the lateral extent of the outer cnemial crest, but they are more like
Bucephala in that the peak is directed farther proximad. Lophodytes
generally has a wider shaft (5.2 to 5.8 percent of the length) than
Bucephala (4.8 to 5.4), whereas Mergellus is thinner (5.0) than Lopho-
dytes.
Clangula and Histrionicus differ slightly from the scoters in that
the enlarged external ligamental prominence protrudes beyond the rim
of the external condyle. In Histrionicus, but not in Clangula, the an-
teroproximal portion of the external condyle is thicker, and in lateral
view it appears more circular, less elliptical. No significant differences
were noted between the tibiotarsi of Melanitta and Oidemia.

TRIBE OXYURINI (STIFF-TAILED DUCKS). The stiff-tailed ducks are sep-
arable from the eiders and sea ducks by the following properties of the
tibiotarsus: (1) The internal condyle overhangs the anteromedial edge
of the shaft to a greater extent than in the other two tribes. (2) The
external ligamental prominence is enlarged so that it extends well
lateral of the condyle.
Heteronetta is the least specialized of the four genera available. Its
tibiotarsus appears intermediate between those of the other stiff-tails
and those of the nondivers: (1) The condyles are displaced farther
medially than in nondiving ducks, but not to the extent found in other
divers. (2) The external condyle extends farther distad than the in-
ternal condyle as in the nondivers. (3) The amount of anterior over-
hang of the internal condyle is greater than in the nondivers, but less
than in other stiff-tails. (4) The outer cnemial crest is directed more
laterad, less anteriorly. In this respect Heteronetta resembles non-
diving ducks, and not stiff-tails. (5) The shaft is thinner (4.1 percent
of length) than in other stiff-tails (5.0 to 6.4 percent).
Nomonyx appears less specialized for diving than either Oxyura or
Biziura. Its tibiotarsus has the following characteristics: (1) The ex-
ternal condyle extends farther distad as in the nondivers and Heteron-
etta. (2) The external ligamental prominence is obscure in anterior
view. (3) The direction of the outer cnemial crest is intermediate be-
tween Heteronetta and the other stiff-tails. (4) The inner cnemial
crest lacks the long ridge found in the more specialized genera of the
tribe. (5) The shaft width (5.4 percent of length) is similar to that of
Oxyura (5.0 to 5.4), thicker than Heteronetta (4.1), and thinner than
Biziura (6.4).
Oxyura and Biziura share the following features of the tibiotarsus:
(1) The distal extent of the two condyles is equal or subequal. (2) The


Vol. 6







WOOLFENDEN: OSTEOLOGY OF WATERFOWL


external ligamental prominence is obvious in anterior view. (3) The
outer cnemial crest is directed more anteriorly than in the two less
specialized stiff-tails. (4) The inner cnemial crest possesses a ridge that
extends distally beyond the proximal end of the fibular crest.
Although the tibiotarsi of Biziura and Oxyura are quite similar, at
least three good qualitative characters separate them. (1) In Biziura
the shaft is thicker, 6.4 percent of the length, as opposed to a maximum
of 5.4 percent in the other genera. (2) In Biziura the shaft is virtually
straight in lateral view. In Oxyura and Nomonyx a distinct curvature
makes the posterior side concave. (3) In Biziura the proximal edge of
the outer cnemial crest is virtually a straight line; in Oxyura it is deep-
ly concave.
Tarsometatarsus
The tarsometatarsus is the best taxonomic element of the leg. The
many articulating surfaces partly account for its usefulness. As with
other leg bones, adaptive modifications frequently obscure the more
basic features.
ANSERANATINAE
Anseranas has many distinctive tarsometatarsal features: (1) The
median calcaneal ridge of the hypotarsus is greatly enlarged. In all
other waterfowl the median ridge is the largest of the four, but it is
not proportionately as large as in Anseranas. (2) The facet for metatar-
sal I is deep and prominent, possibly as a reflection of a stronger hind
toe useful for perching; other waterfowl show virtually no evidence of
this facet. (3) The shaft in lateral view is thin. In other waterfowl the
shaft is thicker, especially distally. (4) The wing of the trochlea for
digit II is greatly enlarged. (5) The trochlea for digit II lacks a pro-
nounced median groove. (6) The external rim of the groove of the
trochlea for digit IV is extended posteriorly.
ANSERINAE
One feature of the tarsometatarsus indicates a close relationship be-
tween the whistling ducks and the swans and geese. The trochlea for
digit II has a prominent lobe on the anterior side at the point of the
most proximal extent of the articulating surface.
TRIBE DENDROCYGNINI (WHISTLING DUCKS.) The following distinguish-
ing characteristics of the tarsometatarsus of Dendrocygna seem most
important: (1) The anteromedial edge is sharply ridged. (2) The in-
ternal cotyla is deeply cupped by a proximal extension of the internal
edge. (3) The shaft is rather uniform in width. (4) The trochlea for


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BULLETIN FLORIDA STATE MUSEUM


digit II lacks a prominent median groove, and the internal edge has a
pit that extends distally to bisect the articular surface. Anseranas is
the only other anatid without a groove in the second trochlea.

TRIBE ANSERINI (SWANS AND GEESE). The tarsometatarsi of swans and
geese show a marked resemblance to those of sheldrakes. From water-
fowl other than sheldrakes, the swans and geese can be separated by
the following tarsometatarsal features: (1) The trochlea for digits II
and IV, and particularly II, are spread. (2) The shaft is narrow in an-
terior view, and the external edge has a prominent curve. In other
waterfowl the external margin is usually a straighter line onto the
trochlea for digit IV.
The following additional features aid in separating swans and geese
from sheldrakes: (1) The trochlea for digit II in internal view is direct-
ed more posteriorly and proximally. (2) The distal foramen in poster-
ior view appears more nearly perpendicular to the shaft. True swans
differ slightly from geese in that the groove in the trochlea for digit IV
continues anteroproximally to the most proximal part of the trochlea.
In geese the groove is interrupted by a swelling. Coscoroba has a
swelling, but this is smaller than in geese.
Individual differences and the size differences permit the separa-
tion of many swan specimens, but consistent criteria of a qualitative
nature are nonexistent. Howard (1946) remarks that in the swans gen-
eric distinctions are less apparent in the tarsometatarsus than in some
of the other elements, and my observations agree. Even Coscoroba
cannot be satisfactorily characterized from this element. In geese, as
opposed to other waterfowl, the trochlea for digit IV has a prominent
swelling at the proximal end of the anterior surface of the trochlear
groove.
The present series of goose tarsometatarsi supports the statement
made by Miller (1937) that no one feature serves to differentiate Branta,
Anser, or Chen. It is even difficult to identify tarsometatarsi of these
three genera by a combination of characters, although Miller feels this
can be done. With Eulabeia and Cygnopsis included the task is even
more difficult. The characters for Branta, Anser, and Chen, according
to Miller, are as follows: Branta shows an inflation of the lateral mar-
gin just distal to the head, which is less pronounced in Anser and usual-
ly is lacking in Chen. In Branta the trochlea for digit II joins the shaft
of the bone at a more abrupt angle and is shorter than in Anser and
markedly shorter than in Chen. Branta nigricans is not typical of the
genus in this respect.


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


In Anser the median side of the hypotarsus makes a less acute angle
with the remainder of the medial surface; the tendinal groove of the
anterior surface is more prominent, and the entire bone is slightly more
stocky than in Branta or Chen. The tarsometatarsus of Anser averages
wider (7.9 to 9.0 percent of total length) than in Branta (6.3 to 8.0) and
Chen (6.6 to 7.9), but it is difficult to substantiate any of the other char-
acters listed above. Furthermore, no characters were found for Eula-
beia or Cygnopsis other than that they are both robust with widths
7.9 and 9.1 to 10.8 percent of the total length, respectively. The ex-
tremely wide tarsometarsi in the available specimens of Cygnopsis are
possibly a reflection of the many centuries of domestication of certain
strains of the species.
The tarsometatarsus of Nesochen is distinctive. The outer margin
of the shaft is straighter than in any other goose, and the shaft is wide
(8.0 percent of total length). In addition, the trochleae are directly in
line with the shaft. Miller states that this latter feature is to be associ-
ated with running habits.
Miller found the tarsometatarsus of Philacte markedly different
from those of Anser, Chen, Branta, and Nesochen. The plantar surface,
just proximal to the trochlea, is stated to be much flatter and broader
and the trochlea for digit II more sharply deflected medially. The one
specimen in the present series, unfortunately poorly preserved, does
not have these features.
ANATINAE
Although the Anatinae are easily distinguished from Anseranas and
Dendrocygna through the presence of a prominent groove in the troch-
lea for digit II of the tarsometarsus, it is difficult to separate them from
the swans and geese with this element. Only two features, both weak,
can be listed: (1) The trochlea for digit II in internal view is slightly
more in line with the other two instead of being deflected more postero-
proximad. (2) The distal foramen in posterior view is more oblique,
less nearly perpendicular to the shaft.
The shape and position of the trochlea for digit II divides the Ana-
tinae into two groups, the nondiving sheldrakes, dabbling ducks, and
perching ducks, and the diving pochards, eiders, sea ducks, and stiff-
tailed ducks. In the nondivers the trochlea for digit II is shorter
(length measured parallel to the shaft), and it extends farther distad.
The median ridge of this trochlea extends distally beyond the level of
proximal extent of the facet of the trochlea for digit III, as seen in ven-
tral view. In the divers the distal end of the median ridge of the troch-
lea for digit II fails to reach the level of the proximal end of the facet


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82 BULLETIN FLORIDA STATE MUSEUM Vol. 6

for digit III. Six of the 43 available genera do not fit the system, name-
ly: Tachyeres of the sheldrakes, Merganetta of the dabblers, Meto-
piana of the pochards, Polysticta of the eiders, and Heteronetta and
Nomonyx of the stiff-tails. These forms are discussed under the tribes
to which they are assigned by Delacour (1954, 1956, 1959). Obviously
a correlation between function and structure is involved here, but sev-
eral of the tribes can be characterized as units on structures of more
deep-seated phylogenetic significance.
TRIBE TADORNINI (SHELDRAKES). The sheldrakes resemble the geese in
the form of the tarsometatarsus and can be separated from other
Anatinae because the trochleae for digits II and IV, and particularly
the former, are spread, and the shaft is narrow in. anterior view, with
the external edge displaying a prominent curve out onto the trochlea
for digit IV. Sheldrakes differ from the swans and geese by the char-
acters listed under that tribe.
Within the sheldrake tribe the features of the tarsometatarsus are
most useful taxonomically. The relative distal extent of the trochlea
for digit II separates the tribe into two groups: In Cereopsis, Chloe-
phaga, and Neochen the trochlea for digit II lies farther distad; it ex-
tends beyond the base of the external intertrochlear notch. In Alopo-
chen, Tadorna, Casarca, and Tachyeres the trochlea for digit II lies
more proximad; it does not extend beyond the base of the external in-
tertrochlear notch. Cereopsis and Tachyeres, the two genera that from
other elements seem more closely related to other tribes, are the most
widely separated, and Neochen is nearest to being intermediate be-
tween the two groups.
Cereopsis differs from all other sheldrakes as follows: (1) The in-
tercotylar prominence in anterior view is large and essentially symmet-
rical in outline. In other sheldrakes the prominence is skewed on the
external side, to make the internal cotyla appear deeper. (2) The
trochlea for digit II in anterior view has the groove extending farther
proximad, and (3) it has a more prominent proximomedial swelling.
Neochen differs from Chloiphaga in that the shaft and trochlea are
thinner in anterior view; the shaft measures 6.7 percent of the total
length. Seven specimens of Chloephaga range from 7.2 to 7.9 percent.
The tarsometatarsi of Tadorna, Casarca, and Alopochen are all
rather similar in form. No useful features were found for separating
Casarca from Tadorna, but some allow for separating Alopochen from
the others. In Alopochen: (1) The shaft is thinner, its width ranging
from 6.8 to 7.6 percent of the total length in 3 specimens; in 9 speci-
mens of Tadorna and Casarca the range is from 7.8 to 8.2 percent. (2)






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


The trochlea for digit II extends farther ventrad and has the proximal
edge sloping gently to the shaft; in Tadorna and Casarca the trochlea
is situated more media, and the proximal edge drops off abruptly to
the shaft.
Tachyeres is easily separated from other sheldrakes: (1) The troch-
lea for digit II is longer and lies more proximad; the distal tip does not
extend beyond the proximal extent of the trochlea for digit III. (2)
The shaft is robust, 10.8 percent of the length; the thickest shaft re-
corded for the other sheldrake specimens measures 8.2 percent (Tador-
na). (3) The lobe on the anterior side at the point of the most proximal
extent of trochlea for digit II is small. A prominent lobe in this position
is typical of sheldrakes.
TRIBE ANATINI (DABBLING DUCKS). The dabbling and perching ducks
cannot be separated by tarsometatarsal features. Differences between
the genera are discussed within the arrangement of Delacour (1956,
1959), although some intertribal comparisons are made.
Chaulelasmus and Spatula are indistinguishable from Anas, but
the Mareca tarsometatarsus is distinct: (1) It's shaft is more robust
at the proximal end just below the cotylar area. (2) Its anterolateral
edge is less prominent. In anterior view the shaft appears to taper
more because of these two features. (3) In Mareca the trochleae are
usually smaller.
Malacorhynchus differs slightly from the typical dabblers in that the
trochleae are spread more laterally. Callonetta has a thicker and more
elevated proximal portion of the anteromedial ridge in the one avail-
able specimen. Whether or not this feature would remain valid in a
series remains questionable. Hymenolaimus, although not differing-
markedly from typical dabblers can be distinguished as follows: (1)
The cotylae form almost a right angle with the anterior surface. In
other dabblers and in the perchers the angle is smaller. (2) In distal
view the posterior rims of the trochleae converge. (3) The trochlea for
digit II in posterior view flares more medially.
The tarsometatarsus of Merganetta is the most distinct found in the
dabbling ducks. The median ridge of the trochlea for digit II does not
quite reach the level of the proximal end of the facet for digit III, and
thus it resembles that of the divers. But the trochlea for digit II is
shorter, and the shaft of the bone is thinner (7.3 to 8.0 percent of total
length) than is typical of the divers. It is even thinner than in all the
other members of the dabbling ducks (8.3 to 11.0 percent). An addi-
tional character isolates Merganetta among the dabblers: the antero-
medial edge of the shaft is much lower than the anteroexternal edge.


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The tarsometatarsi of Cairina and Pteronetta can be distinguished
from those of other perching ducks and from the dabbling ducks by
the shape of the middle groove of the hypotarsus. In these two genera
it is shallower than the grooves on either side, and the floor of the
groove does not reach the shaft. Cairina is unique because of its ro-
bust shaft with a width/length ratio of 12.5 to 12.6 percent. The mid-
dle groove of the hypotarsus is by far the shallowest in this form.
Pteronetta has a slimmer shaft, 10.9 percent of the total length, and the
groove, though shallow, is deeper than in Cairina.
Two perchers, Amazonetta (7.9 percent of total length); and Plectro-
pterus (7.7 to 7.8 percent) have thin shafts. Other than in Merganetta
the next thinnest shaft recorded in either the perchers or the dabblers
measures 8.0 percent. The fact that the shaft in Amazonetta is rela-
tively much thinner than in typical dabblers (minimum 8.3 percent)
speaks for its recognition as a genus apart from Anas.
Qualitative features of the trochlea separate the large tarsometatar-
sus of Plectropterus from the small one of Amazonetta. In Plectrop-
terus the trochleae are directed medially and, the trochlea for digit II
extends farther posteriorly. Sarkidiornis is unique in that it has a mas-
sive outer trochlea; the lateral edge of the shaft swings out as a ridge
to meet the trochlea.
Chenonetta has a tarsometatarsus similar in form to that of Aix and
Dendronessa, but it is considerably longer and proportionately slim-
mer. The width varies from 8.0 to 8.9 percent of the total length in two
specimens. Dendronessa (5 specimens) varies from 9.3 to 10.2 percent,
and Aix (11 specimens) from 9.7 to 11.3 percent.
Size separates the four remaining genera into two groups, the larger
Aix and Dendronessa and the smaller Nettapus and Cheniscus. None
of these is separable on qualitative features of the tarsometatarsus.

TRIBE AYTHYINI (POCHARDS). The tarsometatarsus of pochards is gen-
erally thicker than in eiders (width 9.5 to 12.0 and 8.5 to 9.8 percent of
length, respectively), and the external edge is almost straight instead of
flaring sharply to meet the outer edge of the spread trochleae, as in
eiders. It differs from that of stiff-tailed ducks in that the inner cal-
caneal ridge is proportionately smaller, and the shaft in medial view
curves up to meet the trochleae. The greatest similarity is to that of
the sea ducks, from which it can be distinguished as follows: (1) The
shaft is wide proximally and with little lateral compression. (2) The
trochlea for digit III in posterior view forms a slight angle with the
shaft, so that the groove is directed laterally as it passes proximally.


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


(3) The trochlea for digit II has a smaller gap between its medial ridge
and the proximal end of the facet of the trochlea for digit III.
Within the tribe, Metopiana and Netta differ from Aythya in that
the trochlea for digit II in medial view is curved in outline. In Aythya
the posteroproximal tip is extended proximally, and thus a distinct
angle interrupts the curved outline. The median ridge of the trochlea
for digit II surpasses the level of the proximal extent of the facet for
digit III in Metopiana and indicates the genus is less specialized for
diving than either Netta or Aythya.
TRIBE SOMATERIINI (EIDERS). The eiders can be separated from other
waterfowl quite easily by features of the tarsometatarsus. The shaft
is thinner (8.5 to 9.8 percent of total length) than in most other divers.
The large trochleae are spread, and the external edge of the shaft
curves markedly in order to reach the spread trochlea for digit IV. In
other diving ducks the external edge of the shaft is virtually a straight
line.
The tarsometatarsus of the one available specimen of Polysticta
does not show a space between the levels of the medial rim of the
trochlea for digit II and the posterior extent of the facet for digit III,
because the facet tapers gradually to a point; this may not be typical
of the genus. The trochlea for digit II is long, as is typical of divers.
The other two eider genera, Somateria and Lampronetta, possess no
qualitative features to separate them.
TRIBE MERGINI (SEA DUCKS). The external edge of the tarsometatarsus
of sea ducks shows very little curvature, in distinction to that of the
eiders. The inner calcaneal ridge is not so enlarged as in the stiff-tailed
ducks, and the shaft in medial view curves up to meet the trochleae.
The following several tarsometatarsal features in combination should
separate the sea ducks from the pochards: (1) The shaft is laterally
compressed and frequently the narrowest width is through a promin-
ent groove that lies near the proximal end on the median side. (2) The
trochlea for digit III in posterior view is essentially parallel with the
shaft. (3) The gap between the described parts of the trochleae for
digits II and III is wider.
One feature suggests separation of the sea-duck genera into the two
usual groups: In Bucephala and the mergansers the external edge of
the outer trochlea in anterior view is straight or inflected; in Histrioni-
cus, Clangula, and the scoters the external edge is concave and con-
tinuous with the arc of the shaft.
Bucephala can be separated from the mergansers by the size and
direction of the distal foramen. In posterior view particularly, the dis-


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BULLETIN FLORIDA STATE MUSEUM


tal foramen is larger and more perpendicular to the shaft. In the mer-
gansers the smaller foramen lies at a more oblique angle to the axis
of the shaft. In addition the shaft of Bucephala tends to show greater
curvature, and the anterolateral edge is more elevated.
The three merganser genera are distinguishable by the relative
width of the shaft. In the larger Mergus the width varies from 7.7 to
9.1 percent of the total length; Mergellus is intermediate with a figure
of 9.8 percent; whereas Lophodytes is quite stout, ranging from 10.6
to 11.7 percent. No good qualitative features separate the tarsometa-
tarsae of Histrionicus, Clangula, and the scoters, Melanitta and Oide-
mia. The one available specimen of Histrionicus has a lower inter-
cotylar prominence, a smaller distal foramen, and a less elevated antero-
medial edge to the shaft; perhaps some of these are valid features.
TRIBE OXYURINI (STIFF-TAILED DUCKS). The tarsometatarsus of stiff-
tailed ducks can be recognized without great difficulty: (1) The inner
calcaneal ridge is enlarged more than in other Anatinae. (2) In median
view the anterior surface of the shaft is essentially at the same level as
the trochleae; in other divers the shaft curves anteriorly to the elevated
trochleae. (3) The raised anterolateral edge of the shaft is virtually
straight out onto the trochlea for digit IV. (4) The trochlea for digit
IV in distal view has the inner ridge higher and the outer ridge antero-
proximally reduced. (5) The intercotylar prominence has a deeper
anteroexternal notch. (6) The shaft is wide, 10.8 to 16.3 percent of the
total length.
The tarsometatarsi of Heteronetta and Nomonyx have no space be-
tween the levels of the median rim of the trochlea for digit II and the
proximal extent of the facet for digit III. Features 1, 3, 5, and 6 above,
however, are present in these two less specialized genera. The nar-
rower width (10.8 percent of the length) of the shaft and the lack of a
space between the levels of the named parts of the trochleae for digit
II and III identify the tarsometatarsus of Heteronetta.
Nomonyx (12.6) and Oxyura (11.6 to 12.8) are similar in the rela-
tive width of the shaft, but Nomonyx has no space between the levels
of the named parts of the trochleae for digits II and III. Biziura is
very similar in the form of the tarsometatarsus, but the shaft is much
stockier with the width 16.3 percent of the total length.

Pelvis
The pelvis is of little use for classifying the waterfowl. This element
displays remarkable similarity throughout the family, and those dif-
ferences that appear are in the nature of individual variation.


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


One ratio proved somewhat useful, the least width through the ace-
tabula divided by the length of the element. The length was measur-
ed from the most anterior point on the centrum of the first vertebra to
the posterior end of the ilium or ischium.

ANSERANATINAE
Anseranas, as noted by Miller (1919), has the most distinct pelvis of all
the waterfowl: (1) The posterior iliac crest is broad, and sharply angled
at a ridge running posteriad from the antitrochanter, with the larger
portion lying in the horizontal plane. (2) The posterior edge of the
ilium is much shorter than the ischium. (3) The width through the
acetabula is 28.0 to 31.5 percent of the length, greater than in any of
the superficially similar Anserinae, in which the range is from 15.7 to
26.9 percent.

ANSERINAE
The Anserinae as a unit cannot be characterized by the structure of the
pelvis.
TRIBE DENDROCYGNINI (WHISTLING DUCKS). One feature of the pelvis
in Dendrocygna and Anseranas is found nowhere else in the water-
fowl. The ilium is distinctly shorter than the ischium, with the poster-
ior border of the former lying considerably anterior to the posterodorsal
corner of the latter. In other waterfowl the posterior edges of the two
bones form an oblique line, usually with a notch where the two bones
fuse.
TRIBE ANSERINI (SWANS AND GEESE). The relative width through the
acetabula separates the true swans from the geese. The range for 36
swan specimens is 15.7 to 19.4 percent of the length; for 34 goose speci-
mens the range is 19.8 to 26.9 percent. Coscoroba (23.0) falls with the
geese, but between the averages for the swans (17.56) and the geese
(24.19). The relatively greater width of the goose pelvis may be re-
lated to the more terrestrial habits of these birds.

ANATINAE
The pelvis is too poor an element taxonomically to allow for charac-
terizing the diverse subfamily of ducks.
Among the genera assigned to the sheldrakes Cereopsis has the
relative width through the acetabula (21.8 to 22.5 percent) below the
range for the other, more typical, members of the tribe (22.9 to 32.9),
and within the range of true geese. Chloaphaga, Neochen, and Alopo-


1961





BULLETIN FLORIDA STATE MUSEUM


chen (22.9 to 28.3 percent) have relatively wider pelves than Tadorna
and Casarca (28.9 to 32.9 percent).
Within the remaining Anatinae the pelves are usually narrower in
the diving species than in the nondivers. For example, the average
relative width through the acetabula for 82 specimens of nondivers,
Anas, Chaulelasmus, Mareca, and Spatula, is 31.92 percent; in 67 speci-
mens of the diving Aythya the average is 24.46 percent. Rhodonessa
(27.7) and Metopiana (27.66) are intermediate in the width of the pel-
vis; Rhodonessa seldom dives and Metopiana dives less efficiently than
Aythya according to Delacour (1956, 1959).
Hymenolaimus, although a diving species, has a rather wide pelvis
(29.6 percent), whereas in the torrent duck, Merganetta, it is very nar-
row (22.7 to 23.6 percent).
Although the eiders are considered by Delacour (1959) to be closely
allied to the dabblers, the pelvis is narrow. Seven specimens of Som-
ateria and one of Lampronetta average 24.53 percent. This average
lies outside the range of all dabbling ducks except Merganetta, but
within the wide range recorded for the sea ducks. Polysticta has a rela-
tive width of 27.0 percent, beyond the range obtained for the large
eiders (22.5 to 26.1 percent), and near the figures for Histrionicus
(28.5 percent) and Clangula (24.4 to 26.8 percent).
The relative width through the acetabula is not useful for separating
sea ducks from other Anatinae, nor does it support the intratribal
groups (Bucephala and the mergansers, versus Histrionicus, Clangula
and the scoters) that, from other evidence, seem natural. Within the
first of these groups, Bucephala (26.4 to 29.9) and Lophodytes (22.8
to 30.0) have wide pelves in contrast with the narrow pelves of Mergus
(16.2 to 20.7) and Mergellus (21.6). In the other group the wide pelves
of Histrionicus (28.5) and Clangula (24.4 to 26.8) contrast with the
narrow pelves of Melanitta (19.3 to 23.5) and Oidemia (15.4, 18.6 to
20.8).
On the basis of pelvic structure, as with several other structural
elements discussed above, the stiff-tailed ducks are the most distinct
group within the Anatinae. The pelvis is very narrow (14.7 to 21.1
percent) and overlaps that of only a few genera from other tribes.
Nomonyx (19.5 to 20.4 percent) falls within the range of Oxyura (17.4
to 21.1), but it averages significantly broader, 19.91 compared with
18.96 percent, respectively. Biziura has the narrowest pelvis of any
species of waterfowl (14.7 percent).


88


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


Vertebral Column
Verheyen (1955) bases his classification of the waterfowl primarily on
the number of vertebrae in the various regions of the column. Al-
though the present study is concerned mainly with qualitative features
of the appendicular skeleton, counts of vertebrae in addition to those
of Verheyen are presented in table 1. It is interesting that many of
the changes suggested by the present study are supported by these
data.
The four regions in the column-cervical, thoracic, sacral, and caudal
-are defined as in Verheyen.

TABLE 1. VERTEBRAL COUNTS IN WATERFOWL

Species Cerv. Thor. Sacr. Caud. Total Auth.*

ANSERINATINAE
Anseranas semipalmata 20 5 16 6 47 (VI)
19 5 17 6 47 (W1+)
ANSERINAE
Whistling Ducks
Dendrocygna eytoni 18 5 15 7 45 (V1)
arcuata 18 5 15 7 45 (Vl)
bicolor 17 5 15-16 7-8 44-46 (V4)
arborea 17 5 15-16 7-8 44-45 (V3)
17 5 15-16 7 44-45 (W2)
javanica 17 5 15 8 45 (V1)
17 5 15 7 44 (W2)
viduata 17 5 15-16 7-8 44-46 (V8)
17 5 14 8 44 (W1)
autumnalis 17 5 16 6-7 44-45 (V2)
17 5 15 7 44 (W2)
Swans
Coscoroba coscoroba 21 5 18-19 6-7 51-52 (V5)
Chenopis atratus 25 4-5 20-22 8-10 59-61 (V8)
Cygnus olor 24-25 5-6 20-21 9 59-60 (V7)
melancoriphus 22-24 5-6 18-20 8-9 55-57 (V9)
Olor cygnus 24 5 20 7-8 56-57 (V2)
24 5 21 9 59 (W2)
buccinator 23 5 21 8 57 (W1)
columbianus 23 5 20 9 57 (V1)
22-23 5 19-20 7-8 54-56 (W5)

Continued
Counts by Verheyen (1955) are indicated by a V followed by the number of specimens
examined. Additional counts are indicated by a W.


1961







BULLETIN FLORIDA STATE MUSEUM


TABLE 1 (continued)


Species Cerv. Thor. Sacr. Caud. Total Auth.


Geese


Cygnopsis cygnoid

Anser anser

albifrons

erythropus
fabilis

brachyrhynchus
Chen caerulescens

hyperborea
rossi

Philacte canagica

Eulabeia indiaca

Nesochen sandvicensis

Branta canadensis

leucopsis
ruficollis

bernicla


19
19
18
19
19
19
19
20
20
19
19
18
19
19
19
19
19
19
19
19
20
20
19-20
19
19
19
20
20


18
17-19
17
17
19
18
18
19
19
18
18-19
19
19
17
17-18
18
17
19
18
19
19
18
19-20
17
17
17
18
18


7
7
7
8
6-7
7
6-7
7
?
8
6-7
7
6
7
7-8
7
7
7
7
7
7
7-8
6-8
7-8
7-8
8
7-8
8


49
48-50
47
49
49-50
49
48-49
51
?
50
48-50
49
49
48
48-50
49
48
50
49
50
51
50-51
50-52
48-49
48-49
49
50-51
51


(Vl)
(W2)
(Vl)
(W1)
(V2)
(W1)
(V3)
(Vl)
(W1)
(V2)
(V3)
(W1)
(W1)
(Vl)
(W4)
(VI)
(W1)
(Vl)
(Wl)
(Vl)
(Wl)
(VI?)
(W4)
(V2)
(V4)
(W1)
(V3)
(W3)


ANATINAE
Sheldrakes


Cereopsis n.hollandiae

Chloephaga melanoptera
poliocephala
picta
hybrida
Neochen jubata

Alopochen aegyptiaca


(V2)
(W2)
(W4)
(Vl)
(V6)
(Vl)
(VI)
(W1+)
(V5)
(W1)


Continued


19-20
19
16
17
16
16
17
16
16
16


5
4
5
5
5
5
4
4-5
5
5


16-17
18-19
17-18
17
17
16
17
17
17-18
18


7
6-7
7-8
6
6-7
6
7
7
7-8
7


48
48
46
43
44-45
43
45
45
45-46
46


90


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


TABLE 1 (continued)


Species Cerv. Thor. Sacr. Caud. Total Auth.

Casarca tadornoides 17 5 18 7 47 (V1)
17 5 18 8 48 (W1)
variegata 16-17 5 17-18 7 45-47 (V5)
16-17 5 17 7-8 46 (W2)
cana 16 5 18 7 46 (V3)
16-17 5 18 8 47-48 (W2)
ferruginea 16 5 17 7 45 (V3)
radjah 16 5 16 7 44 (V1)
Tadorna tadorna 17 5 17 7 46 (V6)
Tachyeres pteneres 16 5 17 8 46 (V1)
16 5 17 9 47 (W1)
Dabbling Ducks
Anas platyrhynchos 16 5 16-17 7-8 45-46 (V4)
fulvigula 16 5 17 7 45 (VI)
16 5 16-18 7-8 44-46 (W6)
rubripes 16 5 16-17 7-9 45-47 (W5)
poecilorhyncha 16 5 16 8 45 (V2)
16 5 16 8 45 (W1)
superciliosa 16 5 17 7 45 (VI)
luzonica 16 5 16 ? ? (W1)
melleri 16 5 16 8 45 (W1)
undulata 16 5 16 7-8 44-45 (V2)
16 5 16 8 45 (W1)
castanea 16 5 16 7 44 (W2)
flavirostris 16 5 15-16 7-8 43-45 (V3)
crecca 16 5 16 7 44 (V9)
16 5 15 7-8 43-44 (W2)
formosa 16 5 16 7 44 (W1)
falcata 16 5 17 7 45 (W1)
Chaulelasmus streperus 16 5 17 7 45 (V1)
16 5 17 7-8 45-46 (W4)
Mareca penelope 16 5 17 7 45 (V5)
16 5 16-17 7-8 44-46 (W10)
americana 16 5 18 7 46 (V1)
16 5 17 7 45 (W3)
sibilatrix 16 5 17-18 8 46-47 (V3)
16 5 17 7 45 (W1)
Anas bahamensis 16 5 16 7-8 44-45 (V2)
16 5 15-16 7-8 43-45 (W2)
spinacauda 16 5 16 8 45 (V1)
acuta 17-18 5 17 7 46-47 (V2)
17-19 5-6 16-17 7-8 44-48 (W12)


Continued


1961







BULLETIN FLORIDA STATE MUSEUM


TABLE 1 (continued)


Species Cerv. Thor. Sacr. Caud. Total Auth.


Anas erythrorhyncha
angustirostris
versicolor
querquedula
discors

cynaoptera

Spatula platalea

clypeata

Callonetta leucophrys

Malacorhynchus
membranaceus

Hymenolaimus
malacorhynchos

Merganetta armata

Stictonetta naevosa
Rhodonessa
caryophyllacea


Pochards


Netta rufina

Metopiana peposaca


valisineria
ferina

americana

nyroca

collaris

fuligula


16
16
16
16
16
16
16
16
16
16
16
16
16
16

16


16
16
16
16
18

17
17

17
17
17
17
17
17
17
17
17
17
17
17
17
17
17


5
5
5
5
5
5-6
5
5
5
5
5
5
5
5


16
16
15-16
16
16
15-17
16
15-16
17
16
16
16-17
15
15


7
7
8
7
7
7
8
7-8
7
8
7
7
8
8


44
44
44-45
?44-45
44
44-45
45
43-45
45
45
44
44-45
44
44


43
?

45
44
44
45
47

?45
?


5
5
5
5-6
5
5
5
5
5
5
5
5
5
5
5


17
17
17
16-17
17
17
16
17
17-18
17
16
17
16-17
17-18
17


7
8
7-8
7-8
7
8
8
7
7-9
7-8
8
8
7-8
7-8
8


46
47
46-47
46-47
46
47
46
46
46-48
46-47
46
47
45-47
46-48
47


(V1)
(V1)
(V3)
(V4)
(V1)
(W5)
(V3)
(W3)
(V1)
(W1)
(V4)
(W2)
(V1)
(W1)


(Vl)
(W1)

(V1)
(W1)
(Vi)
(W1+)
(Vl)


(Vl)
(W1)

(V2)
(W2)
(V2)
(W3)
(W3)
(V5)
(W1)
(Vl)
(W4)
(V3)
(W1)
(V1)
(W7)
(V4)
(W1)


Continued


Aythya


Vol. 6






WOOLFENDEN: OSTEOLOGY OF WATERFOWL


TABLE 1 (continued)


Species Cerv. Thor. Sacr. Caud. Total Auth.


Aythya affinis


marila


Perching Ducks
Amazonetta brasiliensis

Chenonetta jubata

Aix sponsa

Dendronessa galericulata

Nettapus auritus

Cheniscus pulchellus

coromandelainus

Sarkidiornis melanotos

Cairina moschata

Pteronetta hartlaubi

Plectropterus gambensis

Eiders
Somateria mollissima

spectabilis

Lampronetta fischeri
Polysticta stelleri

Sea Ducks
Melanitta fusca

perspicillata
Oidemia nigra

Histrionicus histrionicus


5
5-6
5
5


(V?)
(W5)
(W1)
(V?)
(W4)
(V2)
(W1)


Continued


18
17-18
18
17-18

15-16
16
17
16-17
16
16
17
16
15
15
15
15
15
14
16
16
16
16-17
16
16
17
17


7
7-8
7-8
7-8

7
7
7
7
7
7
7
7
7
7
7
7
7
7-9
7
7
7-8
7-8
8
8
7
7

7-8
8-9
7
8
9
8


47
46-47
47-48
47-48

43-44
44
45
44-45
44
44
45
44
43
43
43
43
43
42-44
44
44
44-45
45
45
45
46
45

45-46
46-47
44
46
46
45


(Vl)
(W8)
(V9)
(W6)

(V2)
(Wl)
(V1)
(W2)
(V2)
(W3)
(V3)
(W2)
(VI)
(W1)
(VI)
(W1)
(V1)
(W4)
(V2)
(W1)
(V3)
(W4)
(V1)
(W1)
(V2)
(W2)

(V4)
(W5)
(Vl)
(W3)
(W1)
(W1)


7-9
7-9
8
7-9
7-9
8
8


17
17
16
17
16
16


16
16
16
16
16
16
16


5
5-6
5
5
5
5
5


16-17
16-17
17
16-17
16-17
17
16


44-46
45-47
46
44-46
45-46
?45
45


1961


93






BULLETIN FLORIDA STATE MUSEUM


TABLE 1 (continued)


Species Cerv. Thor. Sacr. Caud. Total Auth.

Clangula hyemalis 16 5 16 8 ?44 (V1)
16 5 15-16 8-9 44-45 (W5)
Bucephala islandica 16 5 17 8 ?45 (V1)
clangula 16 5 16 8 45 (V4)
16 5 16 7 44 (W1)
albeola 16 5 15 8 44 (V1)
16 5 15-16 7-9 44-45 (W7)
Mergellus albellus 16 5 16 8 45 (V4)
16 5 16 8 45 (W1)
Lophodytes cucullatus 16 5 17 8 46 (V1)
16 5 16-17 7-8 45-46 (W4)
Mergus serrator 16 5 17 8 46 (VI)
16 5-6 17-18 7-8 45-47 (W7)
merganser 16 5 17 8 46 (V1)
16 5 17-18 8 46-47 (W4)
Stiff-tailed Ducks
Nomonyx dominica 16 5 15 7 43 (V1)
16 5 15 ? ? (W1)
Oxyura jamaicensis 16 5 16 9 46 (VI)
16 5-6 15-17 8-9 44-46 (W4)
vittata 16 5 15 9 45 (V1)
16 5 15 9 45 (W1)
Biziura lobata 16 6 16 7+ 45+ (W1)
Heteronetta atricapilla 16 5 16 8 45 (VI)
16 5 15 9 45 (W1)




The cervical region begins with the axis and terminates with the
most posterior vertebra anterior to the synsacrum lacking a complete
rib, (one composed of both vertebral and sternal parts and an uncinate
process). Usually the last cervical and occasionally the last two cervi-
cals have incomplete ribs composed of the vertebral portion and a rudi-
mentary uncinate process.
The thoracic region begins with the first vertebra supporting a
complete rib and terminates with the last free vertebra anterior to the
synsacrum.
The sacral region is composed of the vertebrae that are fused to
form the synsacrum. Older specimens tend to show greater fusion at
the posterior end of the synsacrum. The fusion accounts for much of
the variation in this region and in the caudal region.


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WOOLFENDEN: OSTEOLOGY OF WATERFOWL


The caudal region begins with the first free vertebra posterior to
the synsacrum and terminates with the pygostyle. Although the pygo-
style is composed of several fused vertebrae, it is counted as one ele-
ment. Older specimens tend to have more vertebrae fused into the
pygostyle to give additional variation in this region.
The vertebrae of large series of a few species were counted to make
certain that the methods in the present study were comparable to those
of Verheyen. When this was established, counts were generally made
to bring the sample up to at least five individuals.

DISCUSSION AND CONCLUSIONS
Study of the postcranial skeleton indicates that the current classifica-
tion of the waterfowl needs reevaluating. Osteological characters of
the taxa as here recognized are summarized below, and the proposed
classification and hypothetical relationships are presented in table 2
and figure 5 respectively.

Family Anseranatidae
Anseranas, the pied goose, has been variously regarded as belonging to
a separate family (Stejneger, 1885; Miller, 1919; Verheyen, 1955), to
a monotypic subfamily (Salvadori, 1895; Boetticher, 1943; Mayr and
Amadon, 1951; Delacour, 1954), to a subfamily that otherwise includes
only Plectropterus (Peters, 1931), to the perching duck tribe of the
Anatinae (Delacour and Mayr, 1945), and tentatively to the sheldrakes
(Newton, 1896: 837).
The details of the postcranial skeleton show conclusively that An-
seranas semipalmata is an isolated and primitive species. The genus is
highly distinct from all other waterfowl genera. Its osteological differ-
ences, summarized below, are far greater than those listed for the
widely recognized nonpasserine family Falconidae (Brodkorb, 1960).
Anseranas should be separated from the other waterfowl as a distinct
family, the Anseranatidae, characterized as follows:
Humerus with (1) prominent medially situated capital shaft ridge,
and correspondingly restricted proximal and lateral extent of external
head of triceps. Carpometacarpus with (2) no notch in external rim
of carpal trochlea; (3) metacarpal II distally curved upwards; (4)
metacarpal III decidedly curved throughout its length; (5) facet for
digit III protruding distally. Sternum with (6) costal margin long;
(7) basin deep, perforated by numerous foramina, and crossed by trans-
verse ridges, its posterior end trilobed. Coracoid with (8) coracoidal
foramen opening into the shaft; (9) sterno-coracoidal process promi-


1961







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TABLE 2.


PROPOSED CLASSIFICATION OF THE ANSERIFORMES


Suborder Anhimae
Family Anhimidae


Anhima


Chauna


Suborder Anseres
Family Anseranatidae
Anseranas

Family Anatidae
Subfamily Anserinae


Tribe Dendrocygnini
Dendrocygna
Stictonetta*


Tribe Cygnini
Coscoroba
Cygnus
Olor

Tribe Tadornini
Plectropterus
Chloephaga
Cyanochen*
Neochen
Alopochen
Tadorna
Lophonetta*

Tribe Anatini
Sarkidiornis
Pteronetta
Asarcornis*
Cairina
Nettapus
Aix
Chenonetta
Amazonetta
Callonetta
Anas
Salvadorina*
Malacorhynchus
Hymenolaimus
Tachyeres


Tribe Anserini
Anser
Branta
Nesochen
Tribe Cereopsini
Cereopsis


Subfamily Anatinae


Tribe Merganettini
Merganetta

Tribe Aythyini
Rhodonessa
Metopiana
Netta
Aythya

Tribe Mergini
Melanitta
Somateria
Polysticta
Camptorhynchus*
Histrionicus
Clangula
Bucephala
Mergellus
Lophodytes
Mergus

Tribe Oxyurini
Heteronetta
Nomonyx
Oxyura
Thalassornis*
Biziura


* Not examined.


Vol. 6





WOOLFENDEN: OSTEOLOGY OF WATERFOWL


nent and knoblike; (10) head wide; (11) neck broad. Scapula with
(12) acromion short; (13) triosseal ridge a knob extending over an-
terior edge. Furculum with (14) furcular process truncate; (15)
pneumatic foramina in crotch; (16) over-all appearance V-shaped.
Femur with (17) posterior intermuscular line displaced laterally; (18)
internal condyle elongated distally; (19) head directed posteriad.
Tibiotarsus with (20) inner cnemial crest straight. Tarsometatarsus
with (21) median calcaneal ridge greatly enlarged; (22) facet for met-
atarsal I deep and prominent; (23) wing of trochlea for digit II greatly
enlarged. Pelvis with (24) postacetabular ilium broadened hori-
zontally; (25) posterior border of illium shorter than that of ischium.
To these osteological characters can be added cranial features re-
corded by other authors: Palatines narrow (Miller, 1919); prevomer
without a posteroventral angle; lacrimal bone with short, descending
process, not reaching halfway to jugal bar; occiput sloping upward
and forward (McDowell, in Delacour, 1954).
In males the trachea is long (approximately 150 cm.) and convo-
luted, situated outside the pectoral muscle on the left side, under the
skin and attached to both by cellular tissue (Gadow, 1891: 723; Dela-
cour, 1954).
Other morphological traits typical of Anseranas are the following:
bill long and strong, deep at base; nostrils small, situated in middle
and close together; lamellae much reduced; rostral nail large, strong,
curved, pointed, and overhanging; lower mandible with a correspond-
ing convex mental tip; forehead and lores naked; wings long; the 1st
primary equaling the 7th, the 2nd to 5th longest; no wing spur; tail
long and square, of 12 rectrices; legs long, a large portion of the tibia
naked; tarsus reticulate; toes long and slender, nails long, curved, and
sharp; hallux long and on a level with anterior toes (Delacour, 1954);
webbing much reduced, extending only half length of toes (Gadow,
1893:154).
The electrophoretic pattern of the egg-white proteins of Anseranas
is readily separable from those of 30 of Peters' genera of waterfowl,
although it has some characteristics in common with these birds' pat-
terns (Sibley, 1960). Unlike all other waterfowl, the wing molt is
gradual, and adults never lack the power of flight. Furthermore the
species exudes a strong, musky smell similar to that of certain parrots
(Delacour, 1954). The general behavior according to Johnsgard
(1960b) is also at variance with all other waterfowl.


1961


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BULLETIN FLORIDA STATE MUSEUM


Some of the characters of Anseranas, particularly those of the hu-
merus, carpometacarpus, sternum, coracoid, skull, and external mor-
phology, show similarities to the Anhimidae. These characters in-
dicate affinities between the Anhimidae and the Anatidae, with the
Anseranatidae forming the connecting link. Therefore, placing the
families Anhimidae and Anatidae in the same order (Wetmore, 1960)
better reflects their relationships than segregating them in two orders
as Stresemann (1959) suggests.

Family Anatidae
With the genus Anseranas given separate familial rank, the remaining
waterfowl, comprising the family Anatidae, can be defined osteological-
ly by the following features.
Humerus with (1) capital shaft ridge lying farther laterad, and con-
sequently depression for external head of triceps more extensive later-
ally and especially proximally. Carpometacarpus with (2) notch in
external rim of carpal trochlea; (3) metacarpal II straight distally; (4)
metacarpal III nearly straight throughout; (5) facet for digit III not
protuding distally. Sternum with (6) costal margin short; (7) basin
shallow with foramina restricted or absent, and no transverse ridges.
Coracoid with (8) coracoidal foramen lacking; (9) sterno-coracoidal
process compressed; (10) head narrow; (11) neck constricted. Scapula
with (12) acromion long; (13) triosseal ridge elongate and not extending
over anterior edge. Furculum with (14) furcular process rounded; (15)
no pneumatic foramina in crotch; (16) over-all appearance U-shaped.
Femur with (17) posterior intermuscular line lying along medial edge;
(18) internal condyle short; (19) head directed laterad. Tibiotarsus
with (20) inner cnemial crest deflected laterally. Tarsometatarsus with
(21) median calcaneal ridge small; (22) facet for metatarsal I obscure;
(23) wing of trochlea for digit II lacking. Pelvis with (24) postacetabu-
lar ilium greatly compressed horizontally; (25) posterior border of ilium
forming a continuous oblique line with the ischium, except in whistling
ducks.
The trachea fails to make a loop under the skin.
The adult sequence of molts includes a flightless stage.
The egg-white profiles of 30 of Peters' genera, distributed through
the 9 tribes of Delacour, are very similar (Sibley, 1960).
Osteological features indicate two main branches of evolution with-
in the family Anatidae. These branches constitute the subfamilies An-
serinae and Anatinae. With two exceptions, Cereopsis and possibly


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Vol. 6




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