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TRANSACTIONS OF WHE
WAGNER PREE INSTIT@TE
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PHILADELPHIA

VOR, VIE

MAY, 1899

WAGNER FREE INSTITUTE OF SCIENCE
MONTGOMERY AVE. AND SEVENTEENTH ST.
PHILADELPHIA

THE SELENODONT

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UENTA EOCENE

BY W. B. SCOTT

WACNERS TREE INSiMTUTE Ole SCIENCE
OP JRL ADVE Die sallia\

-
TERWSPEES
SAMUEL WAGNER, President.
RICHARD B. WESTBROOK, Treasurer. JOSEPH WILLCOX, Secretary.
J. VAUGHAN MERRICK, JR. So), SKIDMORE:
HARRISON S. MORRIS. SAMUEL TOBIAS WAGNER.
cd
FACULTY

HENRY LEFFMANN, A.M., M.D., President of the Faculty.
S. T. WAGNER, B.S., C.E., Secretary of the Faculty.
e
HENRY LEFFMANN, A.M., M.D., Professor of Chemistry.
W. B. SCOTT, A.M., ROBERT ELLIS THOMPSON, A.M.,

Professor of Geology. Professor of History, Literature,
and Political Economy.

Sood WAGNER SBS: (@.E., THOMAS H. MONTGOMERY, JR., Ph.D.,
Professor of Engineering. Professor of Biology.

S. T. SKIDMORE, A.M., Ea Ga EWING Mil):
Professor of Physics. Professor of Botany.

WILLIAM HEALEY DALL, A.M.,
Honorary Professor of Invertebrate Paleontology.

¥

THOMAS L. MONTGOMERY, A.B., CHARLES W. JOHNSON,
Actuary and Librarian. Curator of Museum.

¥

Counsel for the Institute,

WILLIAM W. MONTGOMERY, Esq.

CONTENTS OP oo

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Cf 5088 95. D- G

INTRODUCTION.—American Selenodonts in General
Geology of the Uinta Basin
WHITE RIVER SELENODONTS :
LEPTOMERYCID&.—Lepiomeryx
Lypertragulus
Hypisodus
Protoceras
UINTA SELENODONTS :
I. CAMELIDA.—Ffrotylopus
Systematic position of Protylopus
Leptotragulus .
Systematic position of Lepfotragulus
Il. LrepromMerycip&.—Leptoreodon
Systematic position of Leptoreodon .
Camelomeryx .
Phylogenetic position of Camelomeryx
Oromeryx
Ill. HomacoDONntTip&.—Lunomeryx
IV. OREODONTIDEH.—Lyrotoreodon
Taxonomic position of Protoreodon and relationships of
the Oreodontide
flyomeryx
V. AGRIOCHERIDA.—Prolagriocherus
Taxonomic position of Protagriocherus .
Summary
Conclusions .
Phylogenetic Table : : :
Literature

Explanation of Plates

vii

INTRO DUG rom
-

HE selenodont artiodactyls found in the various Tertiary horizons of
North America may be roughly grouped into two somewhat hetero-
geneous assemblages: (1.) The first group comprises those which are generi-
cally identical with, or are clearly related to, Old World forms, such as the
anthracotheres and the true ruminants (Pecora), and which reached this con-
tinent by migration. (2.) The second group includes the forms indigenous to
America, the successive stages of whose descent may be traced, more or less
completely, through several of the Tertiary formations.

‘Within this second group are found such peculiar and characteristically
North American forms as the Oreodontide, the Agriocheride, the Leptomery-
cide, Protoceras,and Poebrotherium. These forms have greatly puzzled nearly
all the paleontologists who have studied them, and the most diverse opinions
have been expressed with regard to the systematic position and genetic re-
lationships of the various genera. Only concerning the poebrotheres has
there been any general consensus of opinion; they have been well-nigh
universally regarded as representing the main line of tylopodan descent, lead-
ing directly to the camels and llamas of the modern period. For the other
groups we have been accustomed to seek various European connections and
analogues: the anthracotheres, the tragulines, the giraffes, and the deer have
all been called upon to explain the position of these problematical American
forms, though few students of the subject have been able to reach conclusions
which were altogether satisfactory even to themselves.

The principal difficulty in dealing with these peculiar American families
has hitherto lain in the extremely incomplete and fragmentary phylogenetic
series by which they have been represented in the collections. Owing to this
absence of well-defined phylogenetic series, it has been almost impossible to
unravel the complicated tangle of resemblances and differences between the

American and the European groups of selenodonts, and to determine which

1X

xe INTRODUCTION

of these resemblances are to be ascribed to actual relationship, and which of
them have been independently acquired as the result of a more or less parallel
or convergent course of development.

To a considerable extent this difficulty has been removed by the explora-
tions of the last few years. The collections made in the White River and
Uinta formations by Messrs. Hatcher and Gidley for the museum of Princeton
University, and by Dr. Wortman and Mr. Peterson for the American Museum
of Natural History, in New York, have brought together a great number of
new and finely preserved fossils, which shed new and welcome light upon the
problem. For the opportunity of studying the collections belonging to the
American Museum I am indebted to the kindness of Morris K. Jesup, Esq.,
President, and of Professor H. F. Osborn, and gladly take this opportunity of
expressing my cordial thanks to these gentlemen.

The material to be described in the present paper consists principally of
fossils from the Uinta Beds, supplemented by some White River specimens of
Leptomeryx and Hypertragulus, which add in an important way to our knowl-
edge of those genera.

The Uinta is the most ancient of the American Tertiary stages in which
the artiodactyls began to play an important role in the life of the times.
Indeed, the most striking and characteristic feature of the Uinta fauna, as
distinguished from that of the preceding Bridger stage, is in the very marked
increase of the artiodactyls in general and of the selenodonts in particular.
In the Bridger beds selenodonts are very rare as fossils, and not more than
two genera have been described from this horizon, while in the Uinta the
selenodonts are individually the most abundant fossils, and not less than nine
genera of them may be distinguished. More important than this mere increase
in numbers and variety is the fact that the Uinta selenodonts are so obviously
ancestral to those of the succeeding White River stage. It is hardly an
exaggeration to say that the forerunner of every White River selenodont,
except those of Old World origin, may be indicated, with more or less con-
fidence, in the Uinta fauna. This addition to the phylogenetic series is of the
utmost morphological significance, because of the help which it gives in work-
ing out the real taxonomic position of the problematical American families.
That the problems cannot even now be solved in all respects is due to the fact
that the record of most of the lines breaks off with the Uinta, and cannot yet
be traced back into the Bridger in any satisfactory way. This interruption

leaves the question regarding the position of certain families to some extent

INTRODUCTION xi

an open one, families which had already become distinctly differentiated as
such in the Uinta epoch.

The most interesting and striking result to which the study of the Uinta
selenodonts has led is the very unexpected conclusion that, wth the possible
exception of the oreodonts and agriocherids, all of the strictly indigenous North
American selenodonts are derivatives of the tylopodan stem. Paradoxical as
this conclusion may appear, I believe it to be fully justified by the evidence
which will be laid before the reader. The Tylopoda are thus seen to be a
very ancient and highly diversified group, comparable in this respect to the
Pecora, or true ruminants, which they so closely resemble in many features.
The Pecora are an Old World group, which underwent great expansion and
diversification in Eurasia, but did not reach this continent till late Miocene
times, and never attained the importance here that they have so long had in
the Eastern Hemisphere. Their place was to a very great extent taken in
America by the Tylopoda, which ran a course of development in many ways
parallel to that of the Pecora and Tragulina, but with a variety and diversity
of structure, habit, and appearance such as are not attained in either of the
latter groups.

It is this very parallelism with the Pecora which has led most students of
the American selenodonts astray. We have constantly been endeavoring to
find relationships between these forms and the European ruminants or tragu-
lines, where no such relationships existed, but only analogies, parallelisms, or
convergences. The truth appears to be that the indigenous American seleno-
donts make up a natural assemblage of forms, which, with much diversity of
size and structure, are yet all quite closely related among themselves, and
only distantly with the European forms which more or less resemble them.
Just as the Pecora are typically Old World, both in origin and development,
so the Tylopoda are typically New World, and did not reach the Eastern
Hemisphere till the end of the Miocene or beginning of the Pliocene, and then
only in very limited numbers, Came/us and its immediate forerunners being
the only known Eurasian representatives of the group.

It is an admirable example of the keen insight which characterized Riiti-
meyer that he had practically reached this conclusion at a time when the White
River fauna was very imperfectly known, and that of the Uinta not at all. In
a passage which has not attracted the attention it deserves he says of Lepfo-
meryx: “ Die Merkmale des Schadels mit Einschluss namentlich des Unter-

kiefers, scheinen weit eher auf eine nahe Bezichung von Leptomeryx zu den

xii _ INTRODUCTION

in Nordamerika so stark vertretenen Vorlaufern der Camelina (Oreodon, Pro-
camelus, Leptauchenia, etc.), hinzudeuten und denjenigen von Tragulina und
Cervina sehr fern zu stehen..... Nach jeder Richtung scheint mir also
Leptomeryx den hornlosen Wiederkauern des europaischen Miocens sehr fern
zu stehen.” (’83, pp. 98-9.)

The Uinta beds are confined to the comparatively small basin in North-
western Colorado and Northeastern Utah which lies to the south of the
Uinta Mountains. They directly overlie the strata of the upper Bridger
(Washakie substage), and according to Peterson are divisible into two horizons,
which he calls B and C. (See Osborn, ’95, pp. 72-76.) The lower horizon,
B, is transitional from the Bridger, while the upper beds, C, constitute the
typical Uinta. Peterson says of them: ‘We now reach the ¢rue Utnta, or
Brown’s Park, beds of a fine-grained, soft material, much the same in appear-
ance as the characteristic Bad Lands of South Dakota, with the exception of
the color, which is a brick red; in fact, the reddish tinge holds good through-
out the Uinta sediment... . . These uppermost strata of the Uinta basin
have hitherto been reported (by C. A. White) as resting unconformably upon
the underlying Bridger sediment, but no observable breaks were found to dis-
tinguish the true Uinta from the underlying Bridger sediment.” (Loc. cit., p. 74.)

On the other hand, Hatcher believes that there is a distinct angular un-
conformity between the horizons B and C. In favor of this opinion is the
unquestioned fact that the upper beds (C) overlap the lower (B) towards the
north, extending over upon the upturned Cretaceous and older rocks, which
form the flanks of the Uinta Mountains. 7

The north to south extension of the beds is not great at present, but,
doubtless, has been very much reduced by denudation along the southern edge.

The position of the Uinta formation in the geological column is perfectly
clear, both upon stratigraphical and paleontological grounds; it succeeds the
Bridger and precedes the White River in time. It has been customary to call
the Uinta beds Upper Eocene, but much may be said in favor of regarding
them as Lower Oligocene. The Uinta, White River, and John Day form three
successive stages, whose mammalian faunas are most closely connected, and
were the American time-scale constructed without reference to that of Europe,
no student of these horizons would think of distributing them among different
periods. Clearly, the natural arrangement is to make them three stages of

one period or system. In the interests of paleontology it is fortunate that

INTRODUCTION xiii

_ the French observers have reached much the same conclusion regarding the
corresponding horizons in France, and are tending to enlarge the boundaries
of the Oligocene. The White River beds correspond very closely indeed to
the horizon of Ronzon, which is so generally taken as the type of the Middle
Oligocene, while the Uinta corresponds, somewhat less accurately, to the Paris
Gypsum (Lutetian); the latter is now referred by many to the Lower Oligocene,
and the Uinta should receive the same reference, for the two are so nearly

synchronous that they cannot well be separated into different periods.

[Before taking up the principal subject of this paper, the Uinta seleno-
donts, it will be serviceable to give a revised account of certain White River
genera, especially Leptomeryx and Hypertragulus, which will be found neces-
sary for the full comprehension of the Uinta forms. The new material, which
necessitates the revision and modification of several statements in my former
papers (’9I1, a, 4,c; 95, a, 2), was obtained at various times by Messrs. Hatcher,
Gidley and Wells in the White River beds of Nebraska and South Dakota. ]

GEOLOGICAL MUSEUM, PRINCETON, N. J.,
December 1, 1898.

. A. White River Selenodonts.

Famity LEPTOMERYCID.

Leptomery Leidy.

PLATE J., FIGURES I, 2.

N this genus the dental formula is: IZ, C2, P?, M3. The number of upper
incisors is uncertain; so far, only a single specimen has been found in
which part of the premaxillary is preserved, and in this there is the alveolus
for the lateral incisor, but whether the others were present also is not determin-
able. The upper canine is wanting, at least in the only two specimens which
would show this tooth if it were present, for in the immense majority of the
skulls which have been collected the delicate muzzle is broken across in front
of p2. It is possible, though it seems unlikely, that the absence of the upper
canine is a sexual character, and that the two specimens mentioned are of
females. On the other hand, no fragment of a tusk-like canine has ever been
found associated with the numerous individuals so far discovered. The number
of upper premolars is three, p! having disappeared ; the others are quite com-
plex, each having a well-developed deuterocone, which is conical on p2 and p3,
crescentic on p*. Viewed from the outer side, these premolars have a sharp
and trenchant form, while the prominence of the median external rib and of the
anterior and posterior buttresses gives them a trifid appearance. The upper
molars have incompletely formed internal crescents, and are remarkable for
the large size of the anterior and median external buttresses (or styles), and
especially for the great prominence of the rib upon the antero-external crescent,
which is of very unusual degree; that on the postero-external crescent is far
less prominent. |
The lower incisors are procumbent and almost horizontal in position ;

the median incisor is remarkably long and straight, and is also the broadest
of the three; i; is much shorter and more everted, and iz is still shorter.
The lower canine has become an incisor in form and function and is consider-
ably shorter than iz, which it follows without a diastema. The first lower
premolar is isolated by a long diastema in front of and a shorter one behind
it; it is very small and shaped like a canine, and its form immediately suggests

15

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that it once functioned as a canine, but has dwindled because of the loss of
the upper tooth which it opposed. The other premolars increase successively
in size and complexity backward; they are long, low, trenchant, and acutely
pointed, with sharp basal cusps; pz (and more distinctly pz) has an internal
ridge, which incloses a fossette. The lower molars have narrow, compressed
crowns, and display the traguline character of ridges upon the anterior cres-
cents. Indeed, the entire dentition bears considerable resemblance to that of
the tragulines.

The skull (Plate I., fig. 1) is very much more like that of Poebrotherium
and the typical Tylopoda than the mutilated specimens hitherto figured would
lead one to suppose; it has the same elongate, triangular shape, and the same
very long, slender, and tapering muzzle. It is really surprising to see how the
whole character and appearance of the skull are changed, and how its tragu-
line resemblances are removed by the addition of the muzzle. While the skull
of Leptomeryx is in general very much like that of a minute Poebrotherium,
yet there are many noteworthy differences. The orbit is placed much farther
forward, its anterior border being over m1; the zygomatic arch is relatively
stouter, and the glenoid cavity presents a curiously notched appearance when
seen from the side; the auditory bulla is small and is not filled with cancellous
bone, but simple and hollow, and is provided with a long, tubular meatus;
a small facial vacuity is present between the lachrymal, frontal, nasal, and max-
illary. The horizontal ramus of the mandible is very slender and the angle
is very broad, extending much behind the condyle, but does not form the
great, hook-like process which occurs in Poebrotherium ,; the masseteric fossa
occupies a very elevated position upon the ascending ramus of the jaw.

In addition to these obvious and striking differences in skull-structure
between the two genera, there are numbers of minor discrepancies which it is
not necessary to point out.

The neck in Leptomeryx is short, and the odontoid process of the axis is
peg-shaped. The other cervicals are of the normal artiodactyl type, not like
those of the Camelide. The back is much curved, owing to the elongation
of the hind-limbs.

The fore-limb is short and lightly constructed. The scapula is broad and
triangular, and ruminant rather than tylopodan in shape, though not unlike
that of Poebrotherium. The humerus has no very definite characteristic, and
while quite like that of Poebrotherium, its small size gives it a traguline appear-

ance. The ulna is reduced and very slender, but uninterrupted and entirely

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17

free from the radius, which has a broad, antero-posteriorly compressed and
oval shaft. The carpus is quite traguline in appearance, the magnum being
so shifted as to have only a lateral contact with the lunar; it is also coossified
with the trapezoid, which is-very unusual in this group. The manus contains
four complete digits, though the lateral metacarpals (mc. ii. and v.) are exceed-
ingly slender. No anterior cannon-bone is formed.

The hind-limb greatly exceeds the fore-limb in length and stoutness.
The pelvis is like that of Poebrotherium and altogether different from that of
the tragulines in shape, and much the same statement applies to the femur,
though the distal end of this bone is remarkable for the narrowness and length
of its rotular trochlea. The proximal end of the fibula is a short spine
anchylosed with the tibia; the shaft is wanting, and the distal end is a malle-
olar nodule, wedged in between the tibia and the calcaneum. The navicular
and cuboid are coossified, which, like the union of the trapezoid and magnum,
is very rare in this group of selenodonts. A cannon-bone is formed by the
coossification of the median metatarsals (mt. iii. and iv.), to which are attached
the splint-like proximal ends of the lateral pair (mt. ii., v.). The distal end of
the cannon-bone (Plate L., fig. 2) in uninjured specimens is quite deeply cleft,
and shows in a slight but unmistakable way the eversion of the metatarsal
trochlez which is so characteristic of the Tylopoda; the carina is confined to
the palmar aspect of the trochlee. The phalanges are like those of Poe-
brotherium, and the unguals are elongate, slender, and pointed.

That the whole appearance of the skeleton of Leptomeryx and many
details of its structure closely resemble those of the tragulines is not to be
denied, and I formerly referred it to that group with much confidence (‘gIc, p.
360), in this following Cope’s example (’89, p. 121). The new material just
described has convinced me, however, that this reference is erroneous, and that
Riitimeyer was right in regarding it as essentially tylopodan (’83, p. 98), a con-

clusion which Wortman has also reached in his latest paper (’98, p. 100).

Hypertragulus Cope.
PLATE I., FIGURES 3, 4.
This genus is a remarkable variant of the Leptomeryx type, to which it is

obviously allied, though departing less from the main tylopodan stem, as rep-
resented in Poebrotherium and the John Day Gomphotherium.

)
23

The dental formula is: I, C+, P4, M3. From the material at present

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available it is extremely difficult to work out the homologies of the incisors
and canines, but the arrangement appears to be as follows: The upper incisors,
if present at all, are quite unknown, for no specimen has yet been found with
uninjured premaxillaries. The upper canine was preserved, as is indicated by
the alveolus in one individual. The lower incisors are small and very delicate
and somewhat less procumbent than those of Leptomeryx. The lower canine
is not incisiform, and is separated from iz by a very short diastema; it has a
high, slender, pointed, and recurved crown, which is distinctly larger in some
specimens than in others, a difference which is doubtless sexual. The pre-
molars are much simpler than in Leptomeryx. P+ is a simple, sharp, com-
pressed cone, implanted by two widely divergent fangs. P2, which follows pt
after a considerable diastema, is similar but somewhat smaller ; p® is supported
upon three fangs and bears a small internal cusp (deuterocone); p* is, like
that of Leptomeryx, composed of two crescents, internal and external. Unless
what seems to be the lower canine should prove to be a caniniform premolar,
which is extremely improbable, then p; has disappeared; pz is simple, com-
pressed, and conical, implanted by two fangs, and isolated by a long diastema in
front of it and a much shorter one behind; pz is high, acutely pointed, and
simple, but pz has anterior and posterior basal cusps and a small though
distinct deuteroconid. The premolars of AHypertragulus, both upper and
lower, are distinguished from those of Leptomeryx not only by their greater
simplicity of structure, but also by their much smaller extension in the antero-
posterior direction. The molars are much like those of the last-named genus,
and the superior ones have the same extraordinarily prominent median rib
upon the antero-external crescent, but the outer buttresses are smaller and
project less. z

The skull (Plate I., figs. 3, 4) has quite as characteristically a tylopodan
appearance as that of Leptomeryx, though in a somewhat different fashion.
The cranium is well-rounded and capacious, with low and short sagittal crest,
and the forehead is broad; the face narrows anteriorly more abruptly than in
Leptomeryx, so as to give it a more llama-like appearance. On the other
hand, the muzzle is not nearly so long and tapering, which makes quite a dif-
ference in the general look of the two skulls. The orbit is left rather widely
open behind, because of the absence of a postorbital process from the jugal,
and the facial vacuity between the frontal, nasal, lachrymal, and maxillary is
larger than in Lepiomeryx. The top-view of the skull is of strikingly tylopo-
dan character. (Plate I., fig. 4.) The mandible has a shorter horizontal ramus

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WHITE -RIVER SELENODONTS 9

than that of Leptomeryx, and the angle approximates much more to the great
hook-like shape seen in Poebrotherium.

The ulna and radius are codssified, but the manus, so far as it is known,
does not differ in any important way from that of Leptfomeryx. ‘There is no
cannon-bone in the pes, the two functional metatarsals (iii. and iv.) remaining
separate ; vestigial splints representing mt. ii. and v. were probably present also,
but they have not yet been recovered.

That Aypertragulus is nearly connected with Leptomeryx, and at the same
time is a member of the Tylopoda, appears from its entire structure and from
a comparison with the typical members of that group which preceded or
accompanied it in time. It must be remembered, in considering the system-
atic position of these genera, that the early tylopodans differed in many

important respects from the modern representatives of the suborder.

Hypisodus Cope.

The little animals comprising this genus are the smallest known members
of the family. They differ from all the others in having hypsodont molars
and in the peculiar character of the anterior lower teeth, the canine and first
premolar having taken on the form and function of incisors, which thus appear
to be ten in number in the mandibular series. Very little is known of the
skeleton, but that little leads us to infer that the foot-structure was very simi-
lar indeed to the condition found in Leptomeryx, except that there was no

cannon-bone in the pes.
Protoceras Marsh.

Professor Marsh (91, p. 82) has proposed the formation of a separate
family for the reception of this extraordinary genus, but this seems hardly
necessary, for in essentials Profoceras does not differ more from Leptomeryx
or Hypertragulus than they do from each other, despite its bizarre appearance.

The dental formula is: 13, C+, P4, M%. The upper incisors have entirely
disappeared, but the canine is, in the males, a large curved tusk of D-shaped
section and abraded upon the posterior face; the lower canine has gone over
to the incisors, and its place is taken, in the males, by pz. P+ is isolated
by diastemata in front of and behind it; the other premolars, both upper and
lower, are much as in Leptomeryx, but their great elongation antero-posteri-
orly gives them a strong resemblance to those of Poebrotherium. The
molars also resemble those of Leptomeryx, and in the upper jaw they are

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characterized by the same great prominence of the external buttresses and
ribs, while in the mandible they are broader and lower.

The skull is very remarkable, not only for its bizarre appearance, but
also for its extreme modernization in certain respects, and for the great dif-
ference between the males and females. This skull retains the tylopodan
form only in a very modified way, this form being shown in the prominent
sagittal and occipital crests and in the long, slender, and tapering muzzle.
The cranium is much shortened, the orbit being shifted almost entirely behind
the teeth, and the face is bent down upon the basi-cranial axis, as in the
Cavicornia, a feature which has not been:found in any other White River
mammal. The auditory bulla is hollow and very small. The zygomatic
arch is short, but quite heavy, and the orbit is completely enclosed by
bone. The nasals are extremely short, making the anterior narial opening
exceedingly large, much as in the Saiga antelope. The premaxillaries are
edentulous and their alveolar portion is thin and depressed, but the spines
are broad and the incisive foramina very narrow. The mandible is quite
pecoran in appearance, with a long, slender, horizontal ramus, and a rather
low and broad ascending ramus, with the angle hardly projecting at all
behind the condyle. ‘This latter feature is in marked contrast to most ot
the tylopodan genera. A resemblance to the oreodonts is found in the shape
of the coronoid process, which is very low and tapers abruptly to a blunt
point.

The sexual differences are very striking. In the male skull we find a
pair of compressed, club-shaped, and somewhat horn-like processes on the
parietals, short spines on the frontals, while the free margins of the maxil-
laries rise into massive and everted bony plates. In the females these vari-
ous protuberances are very feebly indicated.

In the vertebral column the neck is moderately elongate and the vertebrze
are not of the characteristically tylopodan structure, but the axis is elongate,
with a broad, flattened odontoid process, like that of Poebrotherium, and a
great hatchet-shaped neural spine, like that of Leptomeryx.

The scapula is, in general, like that of Poebrotherium, but is narrower
and has a very much smaller prescapular fossa, a somewhat shorter acromion,
and a less prominent coracoid. The ulna and radius are separate, except
that in old individuals they may unite distally. The head of the radius has
a broad intercondylar convexity, somewhat as in the oreodonts; distally it

has no contact with the pyramidal. In the carpus the trapezoid and mag-

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21

num are separate, and the carpal elements, especially those of the proximal
row, are high vertically. The metacarpus has four members, of which the
laterals are still well developed, much better than in Leptomeryx.

The hind-limb is considerably longer and stouter than the fore-limb.
The pelvis is like that of Poebrotherium and Leptomeryx, and the femur is a
good deal like that of the former, but is shorter and heavier, its rotular
trochlea is broader, and the suprapatellar fossa less distinct. The tibia is long
and the fibula completely reduced, its proximal end a short spine anchylosed
with the tibia and its distal end a malleolar bone. The cuboid and navicu-
lar are separate, as are the metatarsals. The latter are reduced to two
functional members, while the lateral pair are reduced to splints. The pha-
langes are like those of Poebrotherium, though rather shorter and heavier.

Aside from the extraordinary peculiarities of the skull, especially in the
male sex, Protoceras displays an unmistakable likeness to Leptomeryx and
Fiypertragulus, a likeness which is apparent in the vertebral column, the
limb-bones, the feet, and the dentition. Combined with these are certain
resemblances to Poebrothertum, fewer and less striking ones to the oreodonts,
and a number to the Pecora. It should be remembered, however, that the
pecoran characteristics, which are almost exclusively confined to the skull, are
such as are found only in the /igher Pecora, the Cavicornia, and do not occur
in the deer. It may seem quite absurd to regard Profoceras as an aberrant
member of the Tylopoda, but, as will be shown in the sequel, it is highly
probable that such is the correct view of its relationships. JI am glad to find
myself in agreement with Dr. Wortman on this point, for in the paper already
cited he speaks of “the early cameloids, Protoceras and Leptomeryx.”
(98, p. 102.)

B. Uinta Selenodonts.

Famity I. CAMELID-.

Protylopus Wortman.

PLATE II., FIGURES 5-9.

Bull. Am. Mus. Nat. Hist., vii., p. 104. (April 9, 1898.)
Parameryx Scott (zon Marsh), Proc. Am. Phil. Soc., xxxvii., p. 74. (April 15, 1898.)

N my preliminary paper (loc. cit.), which was printed but a few days after
that of Dr. Wortman, I referred this genus to Parameryx Marsh, with the
extremely vague and unsatisfactory descriptions of which it seemed to agree.
Dr. Wortman, who has seen the type specimens of the so-called Parameryx,
is satisfied that the present genus is distinct from it. He has given (’98, pp.
104-110) an excellent outline description of this animal, the phylogenetic im-
portance of which it is difficult to exaggerate, but a somewhat more detailed
account is necessary for the purposes of this paper. As this genus almost
certainly represents the main line of tylopodan descent in Uinta times, the line
which has led to the modern camels and llamas, it will serve as an admirable
standard of comparison by which to test the divergences of its contempora-
ries. Pyrotylopus is of very great interest as being the most ancient undoubted
member of the tylopodan line, though it sheds less light than could be
desired upon the relations of that line to the other artiodactyl series, for
the peculiar differentiation which is so strongly marked in the White River
genus, Poebrotherium, is already distinct in the Uinta form.

I. Zhe Dentition. The dental formula is unreduced, 13, C+, P4, M3, and
in both jaws the teeth form straight and almost continuous series, slightly
spaced apart, it is true, in the anterior region, but without anything that can
be fairly called a diastema.

A. Upper Jaw. (Plate IL, figs. 5, 6.) The incisors are small and are
arranged in a nearly straight fore-and-aft line, curving inward but very slightly
at the anterior end; they increase somewhat in size from the first to the third,

and are separated by moderate interspaces, with a rather longer space between

>

to

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UINTA SELENODONTS

i)
ww

i and the canine. The crowns are small, laterally compressed and acutely
pointed, of a somewhat hastate shape, and very slightly recurved. The canine
is very small and looks like one of the incisors, which it resembles in form,
exceeding i# in size hardly more than the latter does i#. Thus, at a superficial
glance, the animal appears to have four upper incisors on each side. The
crown of the canine is of somewhat more distinctly hastate shape than that
of i=, expanding below the neck and then tapering to a very acute point; it
is also laterally compressed and its edges are trenchant. It is possible that
the small size of the canines is a sexual character, and that the two finely pre-
served specimens upon which this description is founded are both females,
but the analogy of Poedrothertum would lead us to infer that the size of the
canines did not differ materially in the two sexes.

The premolars are small and very simple, increasing in size and complex-
ity posteriorly. P4, the smallest and simplest of the series, is separated by
short spaces from the canine and p?, which, however, do not deserve the
name of diastemata, as they hardly equal the fore-and-aft diameter of the
tooth itself. In unworn condition the crown of p1 is a simple, compressed
cone, without cingulum or basal cusps, elongated antero-posteriorly and ter-
minating in an acute point; the edges are sharp, and, as the front edge is
convex and the hinder edge concave, the tooth seems to be somewhat re-
curved. P2 is a little larger, but is otherwise very similar, as seen from the
outer side; its transverse diameter is, however, considerably greater and its
external face more strongly convex. In some specimens this tooth has no
cingulum, but in others the cingulum is indicated on the front and hind
edges. P2 is separated by a very short space from p+ and by a still shorter
one from p3, while p® and p# are in contact, or may even overlap. P# resem-
bles p#, except for its somewhat larger size, the presence of a faint inner
cingulum, and its slightly greater transverse width; its anterior edge is sud-
denly narrowed, so as to become trenchant, making a shallow depression
upon the external face, and very feebly marked indications of the basal cusps
may be seen. Sometimes the basal cusps, though small, are quite distinct.
P4 is of nearly the same fore-and-aft length as p, but is decidedly broader,
owing to the development of the deuterocone, which, as in the selenodonts
generally, is of crescentic form. This inner crescent is much better developed
in some individuals than in others, as are also the basal cusps and the ex-
ternal cingulum. In the latter case these cusps are not more conspicuous
than on p*, while in the former they are much better developed on p*. The

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UINTA SELENODONTS

24.
crowns of all the premolars are low vertically, extended antero-posteriorly,
and provided with sharp edges and acute points.

The upper molars are of the strictly tetraselenodont pattern, and unworn
specimens demonstrate the truth of Wortman’s conclusion that the intermedi-
ate tubercles were absent. (’98, p. 106.) These molars differ quite markedly
from those of the contemporary genus, Protoreodon, not only in the absence of
the unpaired cusp (protoconule), which the latter still retains, but also in the
form of the external crescents, which in Protylopus are but slightly concave
on the outer side and have a very prominent median rib, especially the anterior
crescent. The median buttress, which is formed by the junction of the two
external crescents, does not contain a prolongation of the median valley. In
the oreodont, on the other hand, the outer crescents are much more concave
externally and the median rib is less prominent; the outer median buttress is
broader and does contain a narrow prolongation of the median valley.

The molars of Protylopus increase in size from the first, which is the
smallest, to the third, which is the largest of the series, and they are all
slightly different from one another in the details of construction. Differences
between the molars of various specimens may also be observed. In one case
m+ has very small anterior and median external buttresses, and the two outer
crescents are of similar size and shape, with equally prominent median ribs.
In m2 the buttresses are very much larger, and the rib of the postero-external
crescent much less prominent than that of the antero-external one. The
buttresses of m® are still larger, enclosing small fossettes, and the posterior
buttress appears. On m2 and m#a small pillar occurs between the two inner
crescents. In another specimen the anterior buttress on m+ is much larger,
while the median buttress is much less prominent in all the molars.

B. Lower Jaw. (Plate II., figs. 5, 7.) The incisors are small, especially
i;, while i; and iz are much larger and of nearly equal size; they are set
ex echelon in the jaw. The crowns are chisel-shaped, slightly spatulate, and
antero-posteriorly compressed, while those of the upper jaw are laterally com-
pressed. The canine succeeds iz with hardly any interval; it is not much
larger than iz, which it somewhat resembles in shape, but it is more pointed
and continues to function as a canine, opposing the upper canine, which it
slightly exceeds in size. The premolars follow the canine almost without a
break, and are set more closely together than the upper series. P zis almost
caniniform; it is implanted by a single fang and has a compressed, acute,

conical crown, without accessory cusps. The other premolars are much more

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25

elongate antero-posteriorly than pz, and are inserted each by two roots; they
have simple, compressed crowns, with trenchant edges and acute apices, and
are slightly convex on the outer side. Phas small fore and hind basal cusps,
but these are not present on the others. The lower premolars of Poebrotherium
are in general like those the Uinta genus, but they are relatively much more
elongate and have distinct basal cusps.

MEASUREMENTS.
No. 11,222 No. 11,228

Upper dentition, length ‘ : é : é 0.060

*« incisor series, length . , é : : .008 .008

«« premolar-molar series, length : : z .047

«« premolar series, length : : j : -025 .023

‘« molar series, length . ¢ : c . .O215

«« P-1, length : : : : : : .005 .005

GG: eee. GG 3 : Z : ; ; .006 .006

GG oR ey 4G : é : 3 3 : .006 .006

Le Daas é ‘ : : : 5 -006 .005

«« P-4, width ‘ : : : : : -005

«« _M-1, length ; : : : : : .0065 .006

‘© M-1, width z . ‘ B 5 2 .006

«« M-2, length : 6 : é , ‘ .0075 .007

« M-2, width 5 : : 3 ‘ : .008

«« M-3, length ; : : : c c .008 5

« M-3, width A or : j 5 ; .009
Lower dentition, length ¢ : : : 3 .060

‘« premolar-molar series, length a ; ‘ .049

‘« premolar series, length ; : : : .024 .0245

‘« molar series, length . : : . : .025

Coe P-1eslength : F Z : : K .004 .004

Se -2 ee mace 005 006

HSS eer ae 0065 0065

GO rd ey 0065 0065

COU att ye 006 005

CG ae 008 0065 x

Ty ee a oll

The molars require no very particular description, They are of the
ordinary selenodont pattern and increase in size posteriorly; the crowns,
though entirely brachyodont, are relatively quite high, and the outer crescents

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UINTA SELENODONTS

26

are strongly convex externally, with a strong cingulum between them, while
the inner ones are thick and but little compressed. My has a very large fifth
lobe which quite equals the outer crescents in height and length; on its inner
side is a small separate cusp.

As a whole, the dentition of Protylopus is closely similar to that of Poe-
brotherium, and just what we should expect to find in a genus ancestral to
the latter. The incisors and canines are very much alike in the two genera,
but in the White River form the diastema between p+ and p2 in both jaws is
increased in correspondence with the elongation of the face, and the other
premolars have become much elongated antero-posteriorly and have enlarged
their accessory cusps; the molars display a decided tendency to assume the
hypsodont structure, and on those of the upper jaw the external buttresses are
reduced in size. It is of interest to observe that in Poebrotherium the upper
milk-premolars, especially dp*, are more like the true molars of Protylopus
than are the true molars of the White River genus.

Il. The Su// (Plate IL., fig. 5) is very like that of Poebrotherium, though
with many obvious differences. In the first place, it is very much smaller than
in the smallest species of the latter; secondly, the face, and especially its
anterior portion, is much less elongated, while the cranium is narrower and
less capacious. The orbit is smaller and much more widely open behind, and
the auditory bulla has not attained such an exaggerated size. . On the other
hand, there is the same short sagittal crest, the same broad, lozenge-shaped
forehead, narrow, tapering face, and slender jaws. Protylopus has already
acquired the tylopodan physiognomy in a very marked degree, and the skull
immediately recalls that of the llama to the observer, though, of course, the
peculiarities are much less accentuated than in the later members of the
series. So closely does the present genus approximate the contemporary
members of certain other artiodactyl series, that, in the absence of the inter-
mediate forms, it would be difficult to establish its connection. with the
modern Tylopoda.

The skull is, in some respects, of quite an advanced type of structure.
The cranium is short and, for an animal of so early a date, capacious and well
rounded; it supports a short and inconspicuous sagittal crest; the occiput is
low, broad at the base, narrow and rounded at the top, and its crest likewise
is weakly developed. The face is rather long, the orbit being shifted far back,
so that its anterior margin is placed above m*. While remaining of nearly

uniform vertical height throughout, the face narrows much anteriorly, but

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27
does so gradually, not displaying the sudden constriction at p* which is so
characteristic of the modern members of the group.

Unfortunately, the base of the skull is so crushed and concealed in
matrix that very little can be made out concerning its structure. The exoc-
cipitals are broad and low, forming a very broad projection above the foramen
magnum, with a shallow fossa on each side of the prominence; the paroccip-
ital processes are quite long and are compressed antero-posteriorly, tapering
to a blunt point. The supraoccipital is rather narrow and its posterior face
is made up entirely of the median prominence, which extends upward from
the exoccipitals, the lateral fosse being cut off by the narrowing of the
occiput. The supraoccipital appears to extend over upon the dorsal side
of the cranium, but as the sutures in this region are mostly obliterated, it is
not possible satisfactorily to make out the limits of the bone. The mastoid
would seem not to be exposed upon the surface of the skull.

The parietals are relatively very large and roof in nearly the whole of
the cerebral fossa; the sagittal crest is short, low, and thin, soon bifurcating
into two long, low, and curved temporal ridges, which terminate at the frontal
suture near the postorbital processes. Anteriorly the parietals are deeply and
broadly notched to receive a median prolongation of the frontals.

The tympanic is not very well preserved in any of the specimens, but
enough remains to show certain important differences from that of Poebrothe-
vim. For ease of comparison, I shall quote the account of this bone in the
latter genus, which I have given elsewhere (’914, p. 15): “The tympanics are
inflated into enormous bullz, which in both species of Poedbrotherium are
relatively much larger than in the recent genera and are more rounded. In
the small species, P. Wilsonz, they are larger and less compressed than in
P. labiatum, and in both the long diameter is directed nearly parallel to
the cranial axis..... As in the Tylopoda generally, the bulla is filled with
cancellous bony tissue. The external auditory meatus is a closed ring, open-
ing slightly upward and backward; its rim does not project at all beyond
the surrounding parts of the squamosal.” To this description it may be
added that the bulla abuts against the paroccipital process, with which it
unites suturally for the greater part of its length, extending also consider-
ably in advance of the postglenoid process. The auditory meatus is not a
tube, but a mere opening, with a raised lip, into the bulla. In all these
respects the bulla of Protylopus is different from that of the White River

genus, the first and most obvious difference being its very much smaller

28 TRANSACTIONS OF WAGNER
UINTA SELENODONTS

size. It does not come into contact with the paroccipital process at all,
but is entirely contained within the notch between the postglenoid and post-
tympanic processes of the squamosal, and does not extend beneath or in
front of the former process. All of the bulla that is visible in the best pre-
served specimen is a short, transversely placed, and slightly swollen tube,
which projects somewhat below the level of the postglenoid process. Whether
this tube really represents the entire bulla, as it appears to do, it is not yet
possible definitely to decide. The meatus is relatively large and does not
form a complete ring, only the anterior half of the lip being made by the tym-
panic, while the posterior half is made by the posttympanic process of the
squamosal. So far as I can make out, there is no cancellous tissue within
the bulla.

Undue stress has been laid upon the fact that among existing artiodactyls
only the Pecora have the auditory bulla free from cancelli, which occur in
the Tylopoda, Tragulina, and Suina. It is altogether probable that this struc-
ture has been independently acquired by each of the three last-named groups,
for in White River times only Poebrotherium has the cancellous bulla, all
the other known artiodactyls of the time, even the peccary-like Percherus,
having hollow tympanics free from cancelli. The condition of the bulla
found in Protylopus seems to indicate that in the main tylopodan series also
the cancelli were developed after the series had become well established as
such. Concerning the traguline series we have as yet no information, but if
the peccaries and camels acquired the structure independently, there can be
no reason to doubt that the chevrotains did so likewise.

The squamosal is large and makes up much of the sidewall of the cranial
cavity ; inferiorly it forms a shelf which is continuous with the occipital crest,
overhangs the auditory meatus, and in front passes into the zygomatic pro-
cess. The glenoid cavity is a smooth, slightly convex, and indistinctly marked
surface, but the postglenoid process is large, thick, and prominent, forming a
high, transverse ridge. The posttympanic is also well developed, extending
down nearly as far as the postglenoid and enclosing with it a deep notch,
which receives the tympanic. The zygomatic process is slender and rather
short, extending outward but moderately from the side of the skull.

The jugal is quite long, reaching posteriorly almost to the glenoid cavity,
and is but slightly notched to receive the zygomatic process of the squamosal.
The inferior edge of the orbit is prominent, but the postorbital process is

quite low and is widely separated from that of the frontal. The masseteric

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ridge and surface are quite well marked and extend for a short distance upon
the maxillary. Asa whole, the zygomatic arch is rather short, though rela-
tively somewhat longer than in Poebrotherium, decidedly slender and almost
straight, arching outward but little.

The lachrymal is quite largely exposed upon the face in front of the
orbit, but its exact limits cannot well be determined, since only the suture
with the frontal is visible.

The frontals are nearly as elongate in the antero-posterior dimension as
the parietals, though they take little part in roofing the cerebral chamber (as
is also the case in the modern Tylopoda); they are quite broad, the width
exceeding the length. The forehead is broad, smooth, lozenge-shaped, and
very slightly convex, both transversely and longitudinally. Anteriorly the
frontals are deeply notched to receive the nasals, but also send forward a
short, narrow tongue between the divergent ends of the latter; the nasal pro-
cesses are short and blunt. Behind, the frontals give off a broad, triangular
process, which extends into the notch of the parietals already described. The
postorbital processes are quite long and distinct, but are shorter than in
Poebrotherium and much less decurved, leaving the orbit more widely open
behind. The orbit is also conspicuously smaller than in the White River
genus, and not nearly so deep, so that it is well separated from its fellow of
the opposite side, and not, as in Poebrotherium, Leptomeryx, and the tragulines,
divided from it by a mere septum. The supraorbital canal opens much nearer
to the margin of the orbit than in Poedbrotherium, in which it has shifted far-
ther towards the median line, and the groove which runs forward from the
foramen is much less deeply impressed than in the latter. The supraorbital
notch, which in the White River form is very deep, is much shallower in
Protylopus. A small vacuity appears to be formed between the frontal, nasal,
lachrymal, and maxillary. I speak thus hesitatingly, because the fontanelle is
not shown in Wortman’s figure and because it may be due to distortion in the
Princeton specimens, though its shape is so symmetrical that such a mode ot
origin seems improbable. This opening is sometimes present in Poebrotherium.

The nasals are very long and narrow; they are broadest just in advance
of the nasal processes of the frontals, narrowing both anteriorly and poster-
iorly from that point. The hinder ends diverge somewhat and receive
between them the short, narrow median processes of the frontals; anteriorly
the nasals taper gradually to the free ends, which project somewhat beyond the

edges of the premaxillaries. In general, the nasals of Protylopus are much

TRANSACTIONS OF WAGNER
UINTA SELENODONTS

30

like those of Poebrotherium and of nearly the same relative length; they
extend, however, much farther back than in the White River genus, reaching
nearly to the middle of the orbit, while in the latter the fronto-nasal suture is
some distance in advance of the orbit. This posterior extension, in Protylopus,
compensates for the elongation of the anterior part of the muzzle which char-
acterizes Poebrotherium. Another difference between the two genera may be
seen in the shape of the free ends of the nasals, which in the Uinta type are
bluntly pointed and extend beyond the edges of the premaxillaries, and in the
White River form they are emarginated into a semicircular notch, of which
the lateral edges extend farthest forward, but not beyond the premaxille. In
short, in Poebrotherium the frontals have been elongated, pushing the nasals
before them, as it were; at the same time, the whole anterior part of the face
has grown longer, so that, in spite of their less extension backward, the nasals
are relatively as long as before.

The maxillary is much the largest bone of the face, of which it forms
the greater portion; it is very long, but of only moderate vertical height,
which, except in the orbital region, is nearly uniform throughout its length.
In correspondence with the very brachyodont character of the teeth, the
alveolar portion of the maxillary is very low. The masseteric ridge and sur-
face are carried over for a short distance upon the maxillary. The anterior
border, formed by the premaxillary suture, is nearly vertical, but inclines
backward a little at the upper end. In addition to the vacuity or fontanelle
already mentioned, there appears to be another, of narrow, slit-form, between
the maxillary and the nasal. Less uncertainty attaches to this opening,
though it also may possibly be due to dislocation. The infraorbital foramen
is small, narrow, and inconspicuous, and is widely removed from the orbit,
opening above p%, the same position that it occupies in Poebrotherium. From
the general shape of the skull it is plain that the palate was shaped much as
in the latter genus, quite broad behind and contracting very much in front,
where the whole muzzle becomes exceedingly slender. This contraction is
gradual, not abrupt, as it is in the recent Tylopoda.

The premaxillary has a very broad ascending ramus, but in spite of this
extension upon the face, it has but a relatively short contact with the nasal,
because of the absence of any distinct nasal process. For the same reason,
the premaxillary is very widely removed from the frontal, of which the nasal
process is very short. The alveolar portion is short and low, and very nar-

row transversely, because the incisors are arranged in nearly the same fore-

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I
UINTA SELENODONTS 5

and-aft line, in consequence of which the premaxillary has but a slight lateral
curvature. The anterior nares, as in Poebrotherium, have the narrow form
and terminal, vertical position which recurs in nearly all of the primitive
selenodonts, and which is so different from the long, obliquely placed opening
characteristic of the modern Tylopoda.

The mandible is, on the whole, very much like that of Poebrotherium, but
with several minor differences, which tend away from the extreme tylopodan
type as exemplified by the recent members of the series. The horizontal
ramus is long, shallow, compressed, and very slender, with a slightly sinuous
ventral border; it is less elongate than in Poebrotherium, having no edentulous
portion, and is not bent downward at the symphysis, as in the latter. The
symphysis is quite long, extending back to p;, or even to py. From the
hinder end of the symphysis the chin rises gently and regularly to the incisive
alveoli, whereas in Poebrothertum it is depressed and nearly horizontal. The
two halves of the mandible are not codssified, even in aged individuals. The
ascending ramus is low, even lower than in Poedbrotherium, the condyle being
raised less above the level of the molars. The masseteric fossa differs from
that of the latter in being broader and less deeply impressed, in having less
conspicuous borders, and in descending lower upon the ramus. The coronoid
process differs from that of Poebrotherium much as the latter does from that of
the recent genera of the group. In the White River type the process is more
recurved and pointed, shorter and more inclined backward, than in the camels
and llamas. In Protylopus it is still shorter, more inclined, and recurved, and
is altogether like that of a true ruminant. The condyle is small and trans-
versely extended, not having begun to acquire the peculiar, knob-like shape
which is so characteristic of the recent Tylopoda. The angle is prolonged
into a great hook, very much as in Poedrotherium, but as the posterior border
is broken away in all the specimens, I cannot determine whether it is so large
as in the White River genus.

Three mental foramina are present in each ramus of the mandible; the
anterior one, which is the largest and quite conspicuous, is placed beneath py,
while the others, which are mere pin-holes, are situated, one beneath the
hinder border of pz, and the other under the interval between pz and mj.
In Poebrotherium the foramina are much more conspicuous and have a
somewhat different position; one is beneath p,, the second beneath pz,
and the third under mj, nearly the same situation which they occupy
in Auchenia.

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32

UINTA SELENODONTS

MEASUREMENTS.
No, 11,222
Skull, basallength . : : 3 : : : : O.111
Cranium, length to anterior border of orbit . F : : .060
Face, length : : : : : : : : ; -052
Sagittal crest, length . : : : : c : ; O15
Zygomatic arch, length : : : : : , : .040
Mandible, length P : : : F : : : 2.088
gs depth at mz 3 : : : : : : -O13
fe oH Py : : : ‘ : 5 : .O10
ie height of condyle : : : ; : : .026
ef ue coronoid : : d é . : -039

Ill. The Vertebral Column, and especially the cervical region, is but im-
perfectly represented in any of the specimens. The only cervical vertebra which
I have seen is a somewhat imperfect atlas. This, so far as it is preserved,
is quite like that of Poebrotherium; it is short and broad and has a very con-
vex neural arch, with hardly any more than an indication of the neural spine.
The arch is perforated by foramina for the first pair of spinal nerves. Ante-
riorly the transverse processes extend out more widely from the sides of the
vertebra than they do in Poebrothertum, but whether they are carried so far
backward as in the latter I am unable to say. :

The Princeton collection contains no thoracic vertebre, and I shall there-
fore quote Wortman’s account of them: ‘The vertebrae resemble those of
the modern llamas closely in their general proportions. The bodies of the
anterior dorsals are but moderately keeled, and towards the posterior end of
the series strongly keeled; they increase gradually in size from before back-
ward. The neural spine of the fifth is long and recurved, those of the suc-
ceeding dorsals decreasing in length posteriorly. The neural spines of the
last two are considerably shorter and broader, having an almost vertical direc-
tion. The rib facets in the anterior region have their usual relations and
positions, the ribs articulating with the vertebre by two distinct facets, but in
the last two the capitular and tubercular facets appear to be fused together as
in these dorsals of the lama.” (’98, pp. 107-8.)

The lumbars, which, according to Wortman, are seven in number, are
relatively large. The first three have rather short but progressively elongat-
ing centra; those of the next three (4th, 5th, 6th) are of nearly the same size
and shape; they are long, narrow, and depressed, with prominent ventral keels.

The centrum of the last lumbar is shorter, broader, and more depressed than

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those of the preceding three, and has no distinct keel. The transverse pro-
cesses increase in size up to the penultimate vertebra, while the last one has
much shorter and straighter processes; they are long, broad, depressed, and
curved strongly forward. The neural spines are rather low; they incline for-
ward decidedly, except that of the last lumbar, which is nearly erect. The
zygapophyses are of the usual cylindrical, interlocking type, and I can dis-
cover no indication of the additional, or episphenial, processes which from the
faint beginnings in Poedrotherium have become so well developed in the exist-
ing camels. The sacrum is long and very much depressed and is composed
of three or four vertebrae. The anterior one has a broad, heavy centrum and
large pleurapophyses; the posterior vertebre are broad, flat, depressed, and
thin, with low, backwardly directed neural spines, and broad transverse
processes.

The two anterior caudals, which are preserved in connection with the
sacrum, indicate a tail of moderate length; they are short, but have complete
neural arches and spines, prominent zygapophyses, and very large transverse
processes, which have a backward curvature. Except for the greater size of
the transverse processes, these vertebrze are much like the corresponding ones
of Poebrotherium, and doubtless the tail was of similar proportionate develop-
ment in the two genera.

IV. The Fore-Limé is short and slender, decidedly more so than the hind-
limb. The scapula is high and narrow, much narrower than in Poedbrotherium ;
the neck is slender but not abruptly contracted ; the coracoid border, so far as
it is preserved, inclining much less strongly forward, in consequence of which
and of the position of the spine the prescapular fossa cannot be nearly so
wide as in the White River genus; similarly, the glenoid border inclines but
little backward in its course above the neck. In Poebrotherium, on the con-
trary, both borders pursue a very oblique course, which gives great breadth
to the proximal portion of the blade. The spine is high and somewhat
recurved, making the anterior side convex and the posterior concave; the
acromion is both long and high, projecting somewhat outward as well as
downward, but does not descend nearly to the level of the glenoid cavity,
and terminates in a blunt and very slightly recurved point. The acromion is
thus very much smaller than in Poebrotherium, in which the process is far
longer, descending to the level of the glenoid cavity, and is much broadened
and thickened at the end. The glenoid cavity is quite deeply concave, and,
as in the White River type, of nearly circular outline. The coracoid is quite

3

TRANSACTIONS OF WAGNER
UINTA SELENODONTS

34

well developed and forms a stout, incurved hook, roughened at the tip; this
process:is less prominent and massive than in Poebrotherium, just as in the
latter it is smaller than in the existing camels and llamas.

The humerus is, unfortunately, not preserved entire in any of the speci-
mens, the most complete one lacking the proximal end. It may be seen, how-
ever, that the bone is long, slender, and laterally compressed, very much
resembling the humerus of Poebrotherium, though decidedly narrower when
viewed from the front; seen from the side it has the same sigmoid curvature
as in the latter genus. The proximal portion of the shaft has a considerable
fore-and-aft diameter, which gradually diminishes downward, while the distal
portion has but a moderate transverse expansion. The deltoid ridge is very
low and inconspicuous, even less prominent than in the White River genus,
and is in very marked contrast to the great ridge and hook of the modern
tylopodans. The supinator ridge is likewise feebly developed and adds little
to the breadth of the shaft. The anconeal fossa is small, narrow, and deep,
perforating the shaft and forming a minute supratrochlear foramen. The
trochlea is very narrow and set quite obliquely to the long axis of the shaft,
nearly as much so as in Poebrotherium. Considering the geological date of
Protylopus, the humeral trochlea shows quite an advanced type of structure;
it has a considerable vertical diameter and is hour-glass shaped, grooved in
the middle for the corresponding ridge on the head of the radius; the inter-
condylar ridge, which is placed on the outer half of the trochlea, is very weak,
but quite distinct nevertheless.

The bones of the fore-arm are in ordinary adults separate throughout,
although the radius has already begun to increase and the ulna to diminish,
and, as Wortman has shown, coossification takes place in aged individuals at
the middle of the shaft, leaving the proximal ends free. Of the radius I have
no well-preserved example.

The ulna has undergone considerable reduction, and its articulation with
the humerus is altogether posterior. The olecranon is long, narrow trans-
versely, but thick antero-posteriorly, with the free end somewhat thickened
and club-shaped. The coronoid process is prominent, but the sigmoid notch
is rather shallow, for its distal part is incomplete. The shaft is long and quite
slender, tapering rapidly towards the distal end, and has a decided anterior
curvature. For most of its length it is trihedral, with sharp postero-external
and antero internal edges, but the distal portion loses the trihedral form and

becomes laterally compressed and very slender.

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UINTA SELENODONTS

on)

The manus (Plate IL, fig. 9) is highly characteristic and quite different
from that of Poebrotherium.

Of the carpus only the pyramidal, pisiform, magnum, and unciform are
preserved, but these suffice to show some of the more important features of
carpal structure. In the existing Tylopoda the carpus as a whole is broad
and low, which is due to the shortening of the distal elements, the proximal
~ row retaining considerable proximo-distal height. Already in Poebrotherium
this modification makes itself apparent, but in Protylopus it has hardly begun,
the magnum and especially the unciform being quite high in proportion to
their width. The pyramidal is high, narrow, and thick, and has much the
same shape as in /oebrotherium,; it is highest on the radial side, descending
steeply towards the ulnar side. In the last-named genus this carpal is quite
extensively covered by the radius, and in the existing Tylopoda nearly the
whole proximal surface is so occupied. So far as I can make out, this
change has already begun in Protylopus, but if so, the contact with the radius
is much smaller than in the White River genus. While the ulnar facet is of
the usual saddle-shape, that for the pisiform is small and confined to the
postero-external angle of the bone.

The pisiform is shaped much asin Poebrotherium, but is longer, more
slender, and less thickened at the free end. Its proximal facets for the ulna
and pyramidal are not well preserved in the only available specimen, but they
meet at a more acute angle and make the proximal end more pointed than in
the White River form.

The magnum is a small bone, low, broad, and thick, but its breadth
does not exceed its height so much as in the later Tylopoda, and, compared
with the other carpals, it must be regarded as rather narrow; the head is
small and does not rise above the level of the dorsal portion. The scaphoid
facet is larger and more entirely proximal than that for the lunar, while in
Poebrotherium the lunar facet is relatively larger and less oblique than in the
Uinta genus. A comparison of the wedge-shaped space between the mag-
num and unciform in the two genera shows that in Protylopus the lunar must
have had a narrower distal beak, which descended almost to the head of the
third metacarpal. On the radial side the magnum bears a small facet for
the trapezoid, but I can discover none for the second metacarpal.

The unciform is quite a large bone, exceeding the magnum in every
dimension; it is relatively higher and narrower than in Poedbrotherium, though

the difference is not very striking. Most of the proximal end is occupied by

TRANSACTIONS OF WAGNER

6
3 UINTA SELENODONTS

the large, convex facet for the pyramidal, while the lunar facet is relatively
smaller and more oblique than in the White River genus. A large facet
receives the projection of the third metacarpal; it is relatively larger than in
Poebrotherium and vertical, not inclined downward and outward as in the
latter. Another difference is seen in the proportions of the distal facets, that
for the fourth metacarpal being relatively smaller, and that for the fifth much
larger than in the White River type.

One of the features which most clearly distinguish Protylopus from
Poebrotherium is the character of the metacarpus. In the latter it is reduced
to two functional digits (iii., iv.) and two small nodules representing the
proximal ends of ii. and v. In the Uinta genus, on the other hand, there are
four functional digits, though the median pair are considerably enlarged and
the lateral pair much reduced. Wortman’s conjecture as to the composition
of the manus is thus demonstrated to be correct.

In the only manus which the collection contains (No. 11,222) the distal
ends of all the metacarpals are missing, so that their length can be ascer-
tained only approximately ; it is clear, however, that these bones are much
shorter than in Poebrotherium, in proportion both to the length of the metatar-
sus and to that of the other limb-bones.

The first metacarpal may have been present, but if so, it must have been
in a rudimentary condition, and no trace of it is preserved in the specimen.

Metacarpal ii., though apparently not much shorter than mc. ili., is very
slender, but is far more robust than the corresponding metatarsal. The prox-
imal end is narrow but quite thick in the dorso-palmar dimension, and bears a
narrow, plain facet for the trapezoid, but appears not to come into contact
with the magnum. The shaft is straight, very slender, and laterally com-
pressed ; its proximal half is closely applied to me. iii. and is thus flattened on
the ulnar side, having a trihedral section; below this it becomes more rounded.
At the distal end the shaft is slightly expanded and is probably a little wider
than the trochlea.

Metacarpal iii. is longer, much heavier, and in every way differently shaped

from me. ii.;

the proximal end is but little broader than the shaft and its
increased width is principally due to the unciform process. The magnum
facet is quite strongly concave transversely, much more so than in Poebrothe-
rium, in which this facet is nearly plane. The head of me. iii. rises consider-
ably above that of me. iv.,and sends a process which, though not long and not

extending much across me. iv., has yet a large contact with the unciform, rel-

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UINTA SELENODONTS

atively larger than in the White River genus. Though me. ii. appears to have
no contact with the magnum, me. iii. does not reach the trapezoid. The pres-
ent genus, apparently, and certainly its White River successor, are thus in a
stage of transition between the modes of reduction which Kowalevsky has

)

named the “adaptive” and the “inadaptive;” mc. il. is cut off from its con-
nection with the magnum, but mc. iii. has not yet acquired any articulation
with the trapezoid. The shaft of me. ili. is straight and relatively broad, but
much compressed antero-posteriorly and of transversely oval section, though
flattened on the ulnar side by the approximation to me. iv. Distally the two
are slightly separated, but with no marked appearance of that divergence
which is so characteristic of the later Camelide.

Metacarpal iv. is the counterpart of mc. ili., but is a little shorter, the
head not rising so high as that of the latter, though this difference is compen-
sated for by the height of the unciform, which descends below the level of
the magnum; the shaft is also a little broader proximally and more flattened
on the dorsal face; the head is narrow, no wider than the shaft.

Metacarpal v. is the counterpart of me. ii., with which it forms a symmet-
rical pair. The proximal end is very narrow, though it bears a small tubercle
for ligamentous attachment on the ulnar side; the shaft is slightly curved,
with the convexity towards the radial side, while that of mc. ii. is unusually

straight and stiff looking,

MEASUREMENTS.

Scapula, breadth of neck. . : : 7 . KOLOLO
us antero-posterior diameter of glenoid cavity. ; .0095
Humerus, antero-posterior diameter of shaft, proximal . ; .O14
cK breadth of trochlea. ; 2 : : ; .0095

ce height of trochlea F : : é ; : .008
Ulna, length of olecranon : 5 : é : ; .O13
Metacarpal ii., breadth of proximal end : ‘ ; : .003
se ities | te ee of “is : : : 5 .006

LVz,, mee: aC SG ae . 5 : ‘ 2005

ce Vegans a a ae : : : : 004

V. The AHind-Limb is proportionately long and robust, much more
so than the fore-limb. The pelvis is as characteristically tylopodan as the
other parts of the skeleton, and, so far as the material admits of a com-
parison, it much resembles that of Poebrotherium. The ilium is short, but

has a relatively elongate peduncle, which is deep dorso-ventrally and, though

“TRANSACTIONS OF WAGNER
UINTA SELENODONTS

38

compressed, is quite thick; anteriorly the ilium expands into a broad, everted
plate, with rounded and simple crista.. The acetabulum is large and deep.
Both ischium and pubis are broken away, but the section of the former shows
that the spine or crest was low and inconspicuous.

The femur is likewise very tylopodan in appearance. It is considerably
longer and stouter than the humerus, equalling the tibia in length. Proxi-
mally, the bone is broad and carries a large, ovoidal head, set upon a short
neck, and a rather low great trochanter, which does not rise quite so high as
the head. The shaft is heavy, elongate, arched forward, and of nearly uniform
diameter, except at the distal end, where it is somewhat broadened and
thickened. The condyles are rather small and unequally developed, the ex-
ternal one projecting more behind the plane of the shaft. Above the outer
condyle is quite a deep pit for the attachment of the plantaris muscle. The
rotular trochlea is asymmetrical, owing to the prominence of the inner
border, and above the trochlea the dorsal face of the shaft is grooved. In
Poebrothertum the femur is very much like that of the Uinta genus, but has a
somewhat higher great trochanter, a larger pit for the plantaris, a wider
trochlea, and much more prominent condyles. In Leptomeryx also the proxi-
mal end is similar, but broader.

One of the most characteristic bones of Protylopus, and the one which can
most readily be distinguished from contemporary genera of similar stature, is
the tibia. This is stout and quite long, though less elongate than in the later
genera of the series, for it hardly exceeds the skull in length. The proximal
end is narrow and the femoral surfaces rather small and placed very obliquely,
with a low and bifid spine, which is divided by a broad sulcus; the cnemial
crest is very large and prominent and projects forward as a great keel, but is
thinner than in Poebrotherium and does not extend so far down the shaft as in
that genus, but its proximal end is thickened and rugose, and it is deeply
erooved by the sulcus for the extensor longus digitorum. The shaft, which is
almost of uniform breadth throughout, is made trihedral by the cnemial crest,
but where that ceases it becomes transversely oval. The distal end is moder-
ately expanded and very slightly thickened, giving it, when viewed from below,
a rectangular outline; the malleolus is long and heavy and pointed. The ex-
ternal astragalar facet is somewhat the larger of the two, and the intercondylar
ridge is prominent, ending dorsally in a conspicuous tongue-like process. No
sulci invade the articular surface. The fibular facet is partly external and

partly distal, the tibia extending slightly over the distal end of the fibula.

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UINTA SELENODONTS 39

Of the fibula only the distal half is preserved in the most complete speci-
men, but that displays some interesting transitional characters. In Poebro-
therium only the ends of the bone are retained, the proximal end as a short
spine anchylosed with the tibia and the distal end as a malleolar bone. In the
Uinta genus, except, perhaps, in aged individuals, there is no anchylosis, and
the shaft, though reduced to a mere thread of bone, was apparently complete!
At all events, fully half of its length is present in the specimen before us, and
from the appearance of the tibia I should infer that it was uninterrupted.
The filiform shaft is closely applied to the tibia and its distal portion expands
considerably in the dorso-plantar dimension, though remaining extremely
narrow. The distal end forms a stout malleolus, which is partly overlapped
by the tibia; its facet for the calcaneum.is narrow and almost plane.

The pes (Plate II., fig. 8) has more nearly attained the condition found in
Poebrotherium than has the manus, though certain more primitive features
are still to be found. The tarsus is high and narrow, higher and narrower
than in the White River genus, but with similar elements arranged in a
similar way. A small bone, probably the tibiale, is attached to the tibial side
of the astragalus.

The astragalus, like the whole tarsus, is high and narrow; its proximal
trochlea is deeply and narrowly grooved and is quite asymmetrical, the exter-
nal condyle exceeding the internal somewhat in height and very considerably
in breadth. The sustentacular facet is rather narrow and short, and occupies
an oblique position. The distal surface has a narrow facet for the cuboid
and a broad, hour-glass shaped facet for the navicular. In Poebrothcrium a
few changes in the character of the astragalus may be noted; its proximal’
trochlea is more broadly grooved, and in the distal trochlea the cuboidal facet
has become relatively wider.

The calcaneum is quite clongate and has a slender tuber; it is remark-
able for the broad and deep depression which runs for nearly the entire length
of the bone, broadening and deepening distally. On the plantar border the
calcaneum is nearly straight, except that the distal end of this border rises
steeply towards the cuboidal facet. The dorsal border of the tuber rises grad-
ually to the fibular facet, which forms a prominent convexity, rising steeply
on both proximal and distal sides. The cuboidal facet is narrow and so
warped that its plantar portion presents inward as well as distally. The sus-
tentaculum is of only moderate prominence and bears a simply concave facet ;

it is separated from the tuber by a deep sulcus, which runs for a short distance

TRANSACTIONS OF WAGNER

40
UINTA SELENODONTS

along the dorsal side of the latter. In Poebrotherium the calcaneum has
become somewhat more elongate, and has lost all but a trace of the great
external depression, as well as the small sulcus which runs between the
tuber and the sustentaculum.

The cuboid is quite strikingly high, narrow, and thick, much resembling
that of Poebrotherium, but with its proximal facets differently proportioned.
In the White River form the astragalar facet is nearly as broad as that for
the calcaneum, while in the Uinta genus it is decidedly narrower; its dorsal
border is raised high above the calcaneal surface, giving a deeply notched
appearance to the cuboid. On the tibial side the bone is invaded by a sulcus,
which is shallower than in Poebrotherium, and which separates the navicular
facet into dorsal and plantar portions. The calcaneal facet overhangs some-
what, projecting beyond the fibular face of the cuboid; it is strongly convex
in the dorso-plantar direction and is quite complexly warped. The distal
end is almost entirely occupied by the large surface for the fourth meta-
tarsal, that for the fifth being very small. The plantar hook is long and
massive.

The navicular is much shorter vertically than the cuboid, but quite as
broad and thick; its proximal surface for the astragalus is hour-glass shaped,
and the ridge, with its dorsal projection, has a more external position than
in Poebrotherium ; the plantar hook, which in the latter is very much reduced,
is of moderate size and quite conspicuous; it projects down over the ento-
cuneiform, but does not touch it. On the distal end of the navicular are the
usual three facets, of which that for the ecto-cuneiform is very much the
largest and occupies the whole breadth of the bone, while that for the ento-
cuneiform is pushed to the postero-internal angle.

The ento-cuneiform is flat and scale-like, quite high vertically and thick
antero-posteriorly, but very narrow transversely. It articulates with the
navicular by means of a narrow, convex facet, and has a long, oblique surface
which bears against the head of the second metatarsal, while its distal end is
closely applied to the plantar process from the head of the third.

As in most artiodactyls, the meso- and ecto-cuneiforms are codssified, but
their limits may still be made out; the middle cuneiform is much the smaller
of the two elements. The ecto-cuneiform is a large bone, almost as wide as the
cuboid, though its breadth is exceeded by its height, while the dorso-plantar
diameter is relatively hardly equal to half of the same dimension of the

navicular. Apparently, the ecto-cuneiform articulates only with the third

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I
UINTA SELENODONTS as

metatarsal and does not touch the second, though it is possible that a minute
contact with the latter is still retained.

The metatarsus is composed of four members, two of them (iii. and iv.)
enlarged and functional, and two (ii. and v.) greatly reduced and filiform.

Metatarsal ii. has undergone great reduction; its proximal end is very
narrow and compressed, but has a considerable dorso-plantar thickness and is
so wedged in between the ento-cuneiform and mt. ill. as to be hardly visible
when the foot is viewed from the dorsal side. It articulates with the ento-
and meso-, but, so far as I can determine, not with the ecto-cuneiform, The
shaft rapidly tapers to a mere thread of bone, which in one specimen is pre-
served fora length equal to two-thirds of the large mt. iii. and is there broken.
It is therefore impracticable to determine whether the bone was a mere style,
or was furnished with a trochlea and phalanges, as in the tragulines. On the
whole, the former suggestion appears the more probable.

Metatarsal iii. is relatively long and quite heavy, though it has by no
means attained such a proportionate degree of elongation as we find in
Poebrotherium. The head is rather narrow, but very thick in the dorso-
plantar diameter, which is further increased by a prominent projection from
the plantar side. This projection and a similar one on mt. iv. are closely
pressed together and held in place by the ento-cuneiform and the great hook
of the cuboid, between which they are wedged. The head has a broad,
almost plane facet for the ecto-, but appears not to touch the meso-cuneiform,
though in Poebrothertum the latter is covered by mt. ili. and excluded from
contact with mt. ii. In Protylopus the pes, like the manus, is in a state transi-
tional to the adaptive method of reduction, a method which 1s fully attained in
Poebrotherium. The shaft is long, slender, of nearly uniform breadth, though
narrowing to some extent distally, broadening and thickening again just above
the trochlea. In cross-section the shaft is more trihedral and less distinctly
quadrate than in Poebrotherium. The trochlea is shaped almost exactly as in
the latter; it is narrow and low, but well rounded and provided with a
prominent carina, which is confined to the plantar face, and a shallow pit
demarcates the trochlea from the shaft.

Metatarsal iv. is in all respects the counterpart of mt. iii., and in the best
specimen the two are of almost exactly equal length, their proximal ends
lying in the same transverse plane. Save for the proximal facet, which is quite
flat, this bone is not sufficiently different from mt. ili. to require a separate

description.

TRANSACTIONS OF WAGNER

42
UINTA SELENODONTS

Metatarsal v. is rudimentary, but as in the only specimen which retains a
part of it it is broken a short distance below the head, I am unable to say
whether it was elongate and filiform, like mt. ii, though there seems to be
no good reason to suppose that it was not. The proximal end is a little
broader and more club-shaped than that of mt. ii, but is less thickened in
the dorso-plantar diameter, and bears a small, slightly convex facet for the

cuboid. What remains of the shaft is excessively slender and thread-like.

MEASUREMENTS.

Tibia, length ° : 5 ee, : : : 5 ORI
‘« thickness across cnemial crest . 5 : : : .024
«breadth of distal end : j F q : : .013
«« thickness of distal end : é : : - : -0095

Calcaneum, length : p a 5 . 5 0 .033

Astragalus, length é : . : é ¢ : : .O17

fe width of proximal end 6 c : : : .008
UG Ho e* Scistaliend/a\ : : . : . -009

Cuboid, height . . : é ; : 7 . : -O12
ef breadth : : : ¢ ¢ : : é -005
GG thickness 5 3 0 A . . : . -O12

Navicular, height : : : C 6 C 0 : .007

is breadth =. : : ; : c ° . 005
Ecto-cuneiform, height : : : : . 0 -0055
Metatarsal iii., length . 5 : 2 : ; : i .O61

«« pbreadth of proximal end - ; ; ; .006

a a cs ‘« distalend . P 5 5 ; .007

Metatarsal iv., length 5 A A 6 : A ‘ .062
«« breadth of proximal end : 6 . . -005

ee cs ot ‘« distalend . : ; : : .007

Proximal phalanx, fourth digit, length . = : A 3 .020

Second us ue ae ‘s . : . , 5 -O1l

Ungual ue us ue we : - : : Oo SOU

The phalanges much resemble those of Poebrotherium, though they are
more slender in proportion to their length. The proximal phalanx is elon-
gate, narrow, and thin, and is slightly curved, making the approximate side
concave; the surface for the metatarsal is narrow, concave, and notched on
the plantar border for the carina. Towards the distal end the bone contracts
in breadth and especially in thickness; the distal trochlea is less notched

in the median line than in Poedbrotherium, and its articular surface is reflected

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UINTA SELENODONTS 43

much less upon the dorsal side than in the latter. The second phalanx is
much shorter than the first and very slender, especially transversely ; its proxi-
mal trochlea is less distinctly divided into two facets than in Pocbrotherium,
but the distal trochlea is much as in that genus, describing a semicircle
and extending as far upon the dorsal as upon the plantar face. The ungual
also has its proximal trochlea less clearly divided into two facets than in the
White River genus, and it is rather shorter and less tapering. Another dif-
ference from the-latter is the fact that the ungual is not quite so straight,
but is slightly curved, with the concavity directed towards its fellow of the

adjoining. digit.

The Systematic Position of Protylopus.

In my preliminary paper I said of this genus (there called Parameryx):
“There can be very little doubt that Parameryx is the direct and immediate
ancestor of the White River Poebrothcrium, which it so much resembles, and
thus it holds an important place in the main line of tylopodan descent.”
(98, p. 75.) Wortman had independently reached exactly the same conclu-
sion (’98, p. I10), and the foregoing description should render the point suff-
ciently clear. In every detail of its structure the Uinta genus is just what
we should expect to find in the ancestry of the White River form.

In many discussions of phylogenetic problems the reasoning proceeds
upon the assumption, expressed or implied, that the steps of evolutionary
change keep equal pace in the various organs, and that, consequently, if a
given ancestral genus differs from a descendant by a certain amount in the
structure of the teeth, it will also differ by an equivalent amount in the
structure of the feet. Sometimes this assumption is justified, but quite as
frequently it is not, and we find that a genus may have its teeth much more
modernized than its feet, or vice versa, or that the manus and pes represent
different stages of phylogenetic advance, which will be equalized at a later
time in a succeeding genus. Bearing these facts in mind, our examination
of Protylopus completely confirms the suggestion that Pocbrotherium is its
direct descendant, an interpretation which requires no straining of the facts
to make them fit it.

In the first place, we observe that there is marked increase in size in
the descendant genus, an increase which is a very common occurrence in

evolutionary advance. Not that a reduction in size may not occur, but in

TRANSACTIONS OF WAGNER

nr UINTA SELENODONTS

the well-understood phyla an increased stature in each succeeding genus
appears to be the rule.

In the second place, the relative length of the limbs and feet is aug-
mented even more than the enlargement of the head and body.

In addition to these general facts, which are apparent at the first glance,
a detailed comparison of the two genera brings out very many more cor-
respondences :

(1.) The dentition of Protylopus has nearly reached the stage of develop-
ment found in Pocbrotherium, but there are many minor though significant
differences, all of which are in the direction of that greater simplicity
of structure which should characterize an ancestral form. Thus, the incisors
have already attained almost the same condition as in the White River type;
there are no diastemata in the dental series, but what may be called incipient
diastemata are visible in the short interspaces between the canine and p. 1,
and between p. 1 and p. 2. The premolars are of the same type as those of
the succeeding genus, low, elongate, acutely pointed, and trenchant, but they
have not yet acquired such great antero-posterior elongation, and the lower
ones are made simpler by the absence of the basal cusps. The molars are
extremely brachyodont, while those of VPoebyotherium, though still short
crowned, show a distinct tendency towards hypsodontism. We may also
observe changes in the proportionate development of the molar cusps. Thus,
in Poebrotherium the upper molars have become more elongate antero-
posteriorly and narrower transversely ; the external crescents are thinner and
more compressed, the ribs and buttresses much less prominent, and the
valleys narrower and deeper. In the lower molars, the cusps are less conical,
more compressed and plate-like, and the valleys deeper. rotylopus departs
from its White River successor in approximating to the other Uinta seleno-
donts and to the still earlier Bridger types.

(2.) The skull of Protylopus is so like that of Poebrotherium that the
resemblance strikes the observer immediately. The skull has the triangular
shape and long, slender, tapering muzzle which is so characteristic of all the
Tylopoda, but the muzzle is decidedly less elongate than in Poebrotherium ,;
the cranium is narrower, less capacious, and the sagittal crest, though relatively
no longer, is higher and more prominent. The postorbital processes of the
frontal and jugal are shorter, leaving the orbit much more widely open behind,
while the auditory bulla is very small, not reaching the paroccipital process,

and is hollow and free from cancellous tissue. Among the less obvious differ-

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UINTA SELENODONTS 45

ences may be mentioned the following: In /roty/opus the nasals extend
farther backward and in front they are pointed, reaching beyond the premax-
illaries; the supraorbital foramina have not shifted so far towards the median
line, and the grooves leading from them are much shallower, as are also the
supraorbital notches. The mandible has a shorter horizontal ramus and a
lower ascending ramus, but a higher, more recurved, and more ruminant-like
coronoid; the peculiar shape of the angle is much the same in both genera.

It would be interesting in the highest degree to compare the cervical
vertebree of the two forms, but, unfortunately, only the atlas of the Uinta
genus is known, and that is not sufficiently characteristic for the purpose.
The other vertebrz in the latter are somewhat more slender and delicate
than in Poebrotherium, but are essentially like them.

The scapula of Protylopus is higher, narrower, and more slender than that
of its White River successor. The spine is lower and the acromion very
much shorter and more pointed. The humerus is lighter, but otherwise very
similar, but the fore-arm bones remain separate, except in aged individuals,
and though the radius is enlarged and the ulna reduced, the change is less
than in Poedrotherium, in which anchylosis is complete. The manus is farther
removed from that of the White River genus (in which both fore- and hind-
foot have attained the same stage of reduction) than might have been expected
from the advanced development of the dentition, skull, and pes. The carpus is
very much as in the White River genus, except that the distal elements have
not yet been so much shortened proximo-distally. Four functional members
compose the metacarpus, though the lateral elements are very slender and are
more reduced than in other Uinta selenodonts, but in Poebrotherium they are
mere vestigial nodules. The carpo-metacarpal articulations are in a state trans-
itional to the “adaptive” mode of reduction; me. i. still clings to the trape-
zoid, which mc. iii. has not yet reached, but the former has lost its connection
with the magnum. The whole manus is relatively very short.

It is a suggestive fact that the fore-limb of Leptomeryx has many resem-
blances to that of Protylopus, and that almost the only important difference
between them is the coalescence of the trapezoid and magnum in the former.

Pelvis and femur differ very little from those of Pocbrotherium, and the
tibia is also much the same, except that it is proportionately shorter and more
slender, and the fibular shaft, though reduced to a mere thread, appears to be
still complete. The tarsus differs so little from that of the White River type
that it might almost be described as that of Poebrotherium in miniature; the

46 TRANSACTIONS OF WAGNER
UINTA SELENODONTS

metatarsus is much less elongate than in the latter, but in the extreme reduction
of the lateral digits, which are long, filiform splints, the pes is more advanced
in differentiation than the manus. The phalanges are more slender than they
afterwards became, while the unguals are rather shorter and more curved.

Hardly an instance has yet been discovered in which the relationship
between two genera of successive geological epochs is more clearly that of
ancestor and descendant than in the case of Protylopus and Poebrotherium, yet
when we inquire concerning the forerunners of the Uinta type, the answer
must remain doubtful. I see no reason, as yet, to modify my former conclu-
sion (’914, p. 46) that the Bridger genus Homacodon should be regarded as
the probable ancestor of Protylopus, but the gap between the two genera is so
wide that the inference as to their connection must remain largely conjectural.
We need to recover the connecting links, which will doubtless be found in the
Washakie and in the overlying transitional beds, before a definite conclusion
can be reached. The starting-point of the tylopodan line is, probably, as
Cope long ago suggested, the Wasatch TZrigonolestes (Pantolestes), a form
whose exceedingly primitive dentition might be either oreodont or lemuroid.
It seems highly probable that this genus will prove to be ancestral to all of
the indigenous North American selenodonts.

If the conclusion that Poebrotherium and Protylopus are the real, if remote,
ancestors of the modern Tylopoda be well founded, certain inferences of far-
reaching significance for the philosophy of evolution will necessarily follow.

(1.) Schlosser’s dictum (’87, p. 42) that a closed dentition without diaste-
mata indicates the end of a phyletic series is proved not to be tenable, at least
for all cases. Pvotylopus is without diastemata. In the smaller species of Poe-
brotherium they are very inconspicuous, but they become longer and longer in
the later species of that genus and in Gomphotherium, not to mention the suc-
ceeding genera. This growth of the diastemata is, it should be observed,
not due to any loss of teeth, for the John Day genus retains the full number,
but to an elongation of the jaws. The case of the oreodonts is also in point:
the Uinta representative of this family (Protoreodon) has no diastema, and yet
the group flourished abundantly and became highly diversified throughout
the whole of Oliogocene and Miocene times. Schlosser’s principle, though
doubtless true of the cases to which he applied it, is thus seen not to be
of general application.

(2.) In discussing the modes in which evolution acts it has often been

disputed whether development is always by a series of direct and unswerv-:

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UINTA SELENODONTS 47

ing changes in a phylum, each step coming in every detail just so much
nearer to the final result. A study of the horses led me to conclude that
while, as a rule, development is remarkably unswerving in a large sense, yet
in minor details it may pursue a more or less zigzag course. (94, p. 120.)
This conclusion is strengthened by what we believe to be the facts of ty-
lopodan evolution. No difference between the earlier genera of this series
and its modern representatives is more obvious and striking than in the
character of the canine teeth. In Protylopus and FPoebrotherium the canines
are very small and may almost be called incisiform, but from Gomphotherium
onward these teeth become larger and larger until the formidable lacerating
apparatus of the modern type is reached. Even though we should exclude
Homacodon and Trigonolestes from the series, the analogy of all the ungulate
groups, condylarth, amblypod, perissodactyl, and artiodactyl, would justify us in
assuming that the ancestors of Protylopus possessed canines which were of fairly
large size and effective as weapons. If this be true, then the canines first dwin-
dled to very small proportions, only again to enlarge and become formidable.

Another instance of much the same kind is afforded by the history of
the premolars. In Protylopus these teeth are very moderately elongated in
the antero-posterior direction, and in general form resemble those of the con-
temporary selenodont genera and of the White River Leptomeryx. In Poe-
brotherium the premolars have become greatly elongated, accompanying the
elongation of the muzzle, and, as it were, preventing the formation of diaste-
mata. In their antero-posterior length the premolars of Poebrotherium recall
those of Xzphodon. In the John Day, however, this tendency is changed,
and the premolars of Gomphotherium, in their form, revert almost to the
Uinta type, while Procamelus and the subsequent genera of the phylum
are remarkable for the reduction of their premolars both in size and number.
These facts are very significant and have a wider bearing than merely upon

the phylogeny of the Tylopoda.

(?) Leptotragulus Scott and Osborn.

? Parameryx Marsh, Amer. Journ. Sci., 3d Ser., xiv., p. 364 (omen nudunt).
Leptotragulus S. and O., Proc. Amer. Phil. Soc., 1887, p. 258.
? Parameryx Marsh, Amer. Journ. Sci., 3d Ser., xlviii., p. 269.
Parameryx Wortman, Bull. Amer. Mus. Nat. Hist., x., p. 103.

In view of Wortman’s recent attempt to rehabilitate the name “ Para-
meryx,” it will be necessary to say a few words concerning the terms which

TRANSACTIONS OF WAGNER

48
UINTA SELENODONTS

have been applied to this genus. In what follows I assume that Dr. Wortman’s
identification of Leptotragulus with “ Parameryx” is correct, for he has seen the
type specimens, and that my use of the latter name for Protylopus is a mistake.
(98, p. 74.) At the same time I cannot but feel some doubts as to the correct-
ness of the identification, the reasons for which doubts will be explained below.

Professor Marsh (loc. cit.) proposed the name “Parameryx,” in the course
of an address upon the “Introduction and Succession of Vertebrate Life in
America,” without any definition, without any figures, not assigning any
species to the proposed genus, and not indicating in any way that he was
establishing a new genus, or that the name was used for the first time. The
only references made to the animal in the course of the address are as follows:
“With this’ genus is another (Parameryx) also closely allied to Homacodon,
but apparently a straggler from the true line, as it has but three toes behind.”
(77, p. 304.) ‘A most interesting line, that leading to the camels and llamas,
separates from the primitive selenodont branch in the Eocene, probably through
the genus Parameryx.” (Ibid., p. 365.) From such vague allusions as these it
is obviously impossible to identify the genus referred to, and according to
all the codes of nomenclature the term must be regarded as the baldest
nomen nudum, and has no standing whatever. This is especially true be-
cause the single hint of a diagnostic character which is given in the account,
namely, the alleged presence of three toes in the pes, is probably erroneous.
When the name Leftotragulus was proposed the authors had no means of
determining whether or not it was the same as “ Parameryx,’ and thus
were compelled to employ a new term. Seventeen years after his first use
of the term Professor Marsh published a very vague and meagre description of
“ Parameryx” (’94, p. 269), together with figures of an isolated upper molar
and of the astragalus. So far as it goes, this description will apply quite as
well to Protylopus as to Leptotragulus, and hence my use of the name for the
former in my preliminary paper. (’98.)

It was stated above that I do not feel entirely satisfied that the two gen-
eric terms, Leptotragulus and Parameryx, actually refer to the same genus.
Professor Marsh's figure of the astragalus (’94, p. 268, fig. 21), if correctly
referred to the same animal as the upper molar (fig. 20), indicates a form of
totally different proportions from those of Protylopus. While the molar is of
about the same size as in the latter genus, the astragalus is far larger and
equals that of Protoreodon in size. It seems unlikely that the astragalus can

be correctly associated with the tooth, and if they belong to different individ-

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UINTA SELENODONTS 49

uals, no indication is given as to which should be regarded as the type. In
view of these doubtful matters, the question as to the synonomy of Parameryx
and Leptotragulus is not even yet altogether clear.

The dentition of Leptotragulus is still quite imperfectly known, but it
may readily be distinguished from that of any other Uinta selenodont ; it is,
on the whole, most like that of Proty/opus, but differs markedly from the
latter in the presence of a long diastema in front of pz and in the large
caniniform tooth in the mandible. It is still a matter of considerable uncer-
tainty whether this caniniform tooth is a transformed premolar or the true
canine, because in no specimen yet found is the crown of this tooth or of
the incisors preserved. However, the course taken by the fang and the
shape of the remnants of the crown render it more likely that the tooth is
atrue canine. In this case the number of inferior premolars is reduced to
three. The other mandibular teeth very much resemble those of Protylopus,
and thus are easily to be distinguished from those of Leftorcodon and the
other contemporary genera.

The caniniform tooth is large, erect, and slightly recurved, its fang run-
ning upward and forward; so much of the crown as is preserved is of com-
pressed oval section. As already mentioned, the number of lower premolars
is perhaps reduced to three through the loss of the first, though better pre-
served specimens than any which have yet been found may show p; to be
present and caniniform. Between this tooth and py, is a considerable dias-
tema, much as in Leptoreodon. The second premolar is a much compressed,
simple cone, with acutely pointed apex and trenchant edges, and having no
accessory cusps of any sort; in its antero-posterior elongation it resembles pz
in Protylopus rather than that of Leptoreodon. The third premolar has a
crown of similar form, but is provided with a minute antero-internal basal
cusp, and on the posterior half is a low internal ridge, which encloses a very
narrow fossette, almost exactly as in Protylopus. The fourth premolar is
hardly at all larger than the third, which it resembles, except for the larger
size of its accessory elements; it has a high and very sharply pointed princi-
pal cusp (protoconid) and a small, acute, anterior basal cusp, which arises on
the inner side of the crown. From the apex of the protoconid a thin ridge
runs downward and backward, enclosing a narrow, deep fossette between
itself and the outer wall of the crown. /rotylopus has an extremely similar
pz, but the anterior basal cusp is smaller and so completely internal as hardly
to be visible from the outer side.

TRANSACTIONS OF WAGNER
UINTA SELENODONTS

50

The molars also are very like those of Protylopus, though they are nar-
rower and somewhat more like those of Poebrotherium in form. In size they
increase from mj, the smallest, to ms, the largest of the series; all of the
cusps are high and pointed, while the valleys are narrow and deep. The
inner cusps are already laterally compressed and are less conical than in the
other Uinta genera of selenodonts. The two external crescents are widely
separated, while the internal pair are more closely approximated, though with a
deep cleft between them; a transverse valley is thus formed across the breadth
of the crown. Both internally and externally the gap between the fore and
hind crescents is spanned by a cingulum, which has a minute pillar arising
from it, best developed on the outer side. The third molar has a large basin-
like heel, but with a separate cusp on the inner side, which is low and ridge-
shaped, but very distinct. This cusp also recurs in Protylopus, but in none of
the other Uinta selenodonts which have been named. However, a third
genus with the same peculiarity is probably indicated by some specimens
in both the Princeton and New York collections, which are too imperfectly
preserved for definite generic reference.

Of the milk dentition only dp; is known, and this is preserved in a speci-
men (No. 2509) belonging to the American Museum, in which the crown of
the permanent successor (p;) is already almost completely protruded. The
milk-tooth is of the usual selenodont pattern and is composed of three pairs
of crescents, but a primitive feature is to be seen in the comparatively small
size of the anterior pair.

MEASUREMENTS.

No. 11,500 No. 2509} No. 1803}

Lower P-2, length . ; F : 2 .006
P=3,_< “S : : ; . : .006
oh PRA : : . : ; -0065 .006
Dp-4, ‘‘ - Fi ; 5 , .007
UES INES (SU , : ‘ : ; .007 .006 .006
1 : : : : . .0065 .006
Wilke ys 2G 5 ; : : : -O115

The foot-bones which I referred to Leptotragulus in a former paper
(89, p. 482) were not found with the type specimen, which is a fragment of

the mandible; the reference was made on the strength of the tylopodan char-

* Type specimen of genus, Princeton Museum.

j American Museum of Natural History.

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UINTA SELENODONTS

Bil

acter of these bones, and is so uncertain that no dependence can be placed
upon them in attempting to decide the nature of the genus. Wortman
(98, p. 104) has described a remarkable pes which he attributes to Lepto-
tragulus (Parameryx), but the reference is very problematical.

The single well-defined species is Z. proavus S. and O.

The Systematic Position of Leptotragulus.

The difficulty in making a satisfactory reference of this genus lies simply
in our very imperfect knowledge of it, and until we have learned the character
of the anterior teeth and of the feet the difficulty will remain. The similarity
of the lower teeth to those of Protylopus is so very close, even in minor details,
that the genus is included in the same family as the latter, though with a
question, for should the caniniform tooth eventually prove to be a transformed
premolar, it would be necessary to remove Leféotragulus from that family. In
this case the connection of the main tylopodan phylum with Leptorecodon, and
through that genus with the oreodonts, would be made all the closer.

In my former account of Leptotragulus (’89, p. 483) I pointed out that
the presence of only three inferior premolars would, if confirmed by other
specimens, render the known species, at least, ineligible for a place in the
direct line of tylopodan descent. By the discovery of Protylopus, Lepto-
tragulus is made to take its place as a side-branch of that stem. Among
the White River genera Hypertragulus seems to be the one most likely to
have descended from the Uinta form, which would serve to explain its many
resemblances to VPoebrotherium and its intermediate position between the
latter and Leptomeryx. If the lower caniniform tooth of the Uinta genus
should prove really to be a canine, then its position, here suggested as
ancestral to Hypertragulus, would be much strengthened. However, until
much more complete material of the Uinta genus has been collected its

taxonomic position must remain an open question.

Famity Il. LEPTOMERYCID.
Leptoreodon Wortman.
PLATE II., FIGURES 10-14.
Bull. Amer. Mus. Nat. Hist., N. Y., x., p. 95. (April 9, 1898.)
Merycodesmus Scott, Proc. Amer. Phil. Soc., xxxvii., p. 75. (April 15, 1898.)

The following description is founded upon two specimens, one of which,

TRANSACTIONS OF WAGNER
UINTA SELENODONTS

52

the type of MJerycodesmus (Princeton Museum, No. 11,225), consists of the
skull and an imperfectly preserved fore-foot, and the other is a block (No.
11,223) containing parts of two skulls, several vertebra, the pelvis, and hind-
limb nearly complete. While the parts of the skull preserved in the second
specimen are not sufficient to put the reference of it to the present genus
beyond all question, yet there is little room for doubt in the matter. It
certainly cannot pertain to Lepftotragulus, Protylopus, or Oromeryx, and must
belong to some form either identical with or very closely allied to Leptoreodon.

The dentition is exceedingly peculiar, and seems to unite the character-
istics of several distinct families. The formula is: 13, C+, P4, M3.

A. Upper Jaw. (Plate IL, figs. 10, 11.) The incisors are small, conical,
pointed, and slightly recurved; they are much smaller than in Protylopus, but
have a similar shape, and, as in that genus, they are separated by short inter-
spaces and arranged in almost the same fore-and-aft line. A longer space inter-
venes between i* and the canine. The canine is large, very much larger than
in Protylopus, and though laterally compressed, is yet quite stout and thick ; the
anterior border is thickened and rounded, with a deep, narrow groove running
down the external face; in cross section the tooth is D-shaped, much as in the
oreodonts, but thinner and more compressed laterally. As the upper canine is
opposed by the caniniform pj, it is the posterior face that shows abrasion.

The premolars are quite simple. The first is placed near the canine, but
is separated by a long interval from p?; it is implanted by two roots and has
a small, but high, thin, pointed, and trenchant crown, which in shape and
position resembles that of Hypertragulus. The second premolar is like the
first, but is larger, especially in the fore-and-aft dimension; it is somewhat
thickened transversely. The third closely resembles the second when seen
from the outer side, but internally there is a marked distinction, for this tooth
is carried upon three fangs, and in ZL. gracilis has a small but distinct deutero-
cone; in L. mars/u this is “a faint internal cingular ledge.’ (Wortman, ’98,
p. 96.) The fourth premolar is of the well-nigh universal selenodont pattern,
composed of two transversely placed crescents. It remains only to note that
the external wall of the tooth is quite markedly concave, with a low median
rib, and that the inner cingulum is prominent.

The molars are composed of four cusps only,and Wortman was mistaken
in supposing that the anterior intermediate cusp was probably present, as. un-
worn specimens clearly show. They bear considerable resemblance to those
of Protylopus, and, indeed, it is a difficult task to identify scattered molar teeth

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UINTA SELENODONTS

of any of these genera in which the unpaired cusp has been suppressed. In
size the molars increase successively from m1 to m?; they are considerably
wider transversely than long antero-posteriorly, and are of nearly regular
quadrate outline, though the front half of the crown is slightly broader than
the hinder half. The first molar is small, its external crescents have more con-
cave outer faces than in Protylopus, and the external buttresses are but little
larger. On the second and third molars the antero-external buttress has
become very large, much more so than in Proty/opus, but the outer crescents
are more concave than in that genus, and the median rib of the anterior one
is rather less prominent.

B. Lower Jaw. (Plate IL, figs. 10,12.) The incisors are quite procumbent,
and in length diminish slightly from i; to iz, while in breadth the relation is
reversed, iz being slightly broader than i,;; the crowns are simple and chisel-
shaped, broadest at the cutting edge and tapering to the root. The canine
resembles a fourth incisor, and follows upon the third after an interval no
greater than that between i; and iz; the crown is a little shorter and wider
than that of the latter.

The premolars are rather complex for an Uinta artiodactyl and are of
highly characteristic form. The first is isolated by a short diastema in front
of and a much longer one behind it; it is a large caniniform tooth, implanted
by a single fang, and stands much higher than any other of the mandibular
teeth; the crown is simple and quite thick, and is worn obliquely on the
anterior face by the attrition of the upper canine, which it opposes. In shape
and function this tooth is like the caniniform premolar of the oreodonts ; but
this peculiar transformation is not confined to the latter family; it is repeated
in the males of Protoceras, and in Leptomeryx pz, although very small and
almost rudimentary, is in form a canine, and irresistibly suggests that it must
once have functioned in that capacity.

The second premolar is short antero-posteriorly and is carried upon two
fangs; the crown is perfectly simple, high, compressed, trenchant, and acutely
pointed. The third premolar resembles pz, except that it is more extended
antero-posteriorly and has on the inner side of the crown a short, compressed,
plate-like ridge, which runs a short distance back from the central apex and
partially encloses a fossa, that is, however, open behind, very much as in pz of
Leptotragulus. The fourth premolar has a large, conical, internal cusp (deutero-
conid) in place of the inner ridge, a feature which clearly demarcates this
genus from Lepéotragulus.

TRANSACTIONS OF WAGNER

34 UINTA SELENODONTS

The molars considerably resemble those of Leptomeryx, but the cusps
are more conical and less compressed, as well as somewhat smaller, which
makes the transverse valleys wider and separates the two external crescents

more; the external cingulum is quite conspicuous. On mz is a large fifth

cusp, which has a continuous rim enclosing a narrow fossette.

MEASUREMENTS.

Upper dentition, length . : - 0.070 Lower dentition, length . : - 0.072
‘« incisor series, length . O07, ‘incisor series, length . . .0075
“canine, fore-and-aft diameter .005 ‘« canine, fore-and-aft diameter .002
G6 GG transverse diameter . .003 «« premolar-molar series, length, .058
«« premolar-molar series, length, .054 ‘« premolar series, length ee OB2)
‘* premolar series, length nT EO33) ‘« diastema between pz and pz, .0085
«« diastema between p1 and p2, .009 oc Par dengthy. : : . .005
(oe (Parlensthim. ; é = 004! ««P-1, width . ; 5 . 2.003
Ca he ace : : : 5 | ley ‘> B-2-ilensth: : 5 - .005
Ce Wa =3'8 ade 3 : 0 = .0075 Ok SRI oh eee cokes : : - .007
CU eerie iG 5 ; : . .006 HG" Jee dds - F - .0065
«« P-4, width . - : =) EOOOhm| «« P-4, width . 3 : . .004
«« molar series, length =. 21 3022 «« molar series, length. - .026
«« M-1, length ; : . 0065 | «« M-1, length 2 é - .0065
« M-1, width . c . . .0085 | <‘* M-1, width . : : . .0055
‘© M-z2, length A : er ooSam| «« M-2, length 6 é - .0075
«| M-2, width . P ; + -O1O: 4} “ M-2, width . F f . .006
‘« M-3, length 5 5 - 009 | «« M-3, length : : . .O115
«« M-3, width . : : col |) Mes widths : : . .0065

The Sul (Plate II., fig. 10) is in general appearance and character a good
deal like that of Protylopus, but is somewhat heavier and stouter, and the
muzzle is more elongate, especially in the anterior region where the diastemata
in the dentition occur. The tylopodan characteristic of a triangular skull with
its broad cranium and forehead, and slender, tapering muzzle, is very distinctly
displayed. The cranium is relatively well-rounded and capacious and the
sagittal crest is short, though quite prominent, at least in old individuals,
while the temporal ridges are long and converge backward quite gradually
into the short crest. This arrangement prolongs the forehead well behind the
orbits and gives it much the same shape as in Pyotylopus, but the temporal
ridges are far more prominent than in the latter, and separate the forehead

from the brain-case in a more conspicuous way. The orbit is small, with its

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Op)

upper margin rising somewhat above the general level of the forehead, and in
L. gracilis is placed quite far forward, the anterior border being above the line
between mtand m2, while in Z. sarshi this border is above the hinder half
of m2. Despite the long, decurved postorbital process of the frontal the orbit
is quite widely open behind.

In the skulls which I have had the opportunity of examining, most of
the sutures are obliterated, so that it is difficult and often impossible to
make out the limits of the individual bones. The occiput is rather low and
is bounded by a prominent crest ; the condyles are large and extend conspicu-
ously behind the plane of the occiput, and the paroccipital processes also are
curved strongly backward. The coronal suture is not visible in any of the
specimens, but assuming that it occupied the same position as in Protylopus,
then, as in that genus, the temporal ridges must extend for some distance
over upon the parietals, but for a shorter distance and converging more
rapidly to the sagittal crest than in the latter. The sagittal crest is short,
as is the whole postorbital part of the cranium. The parietals are broad and
gently arched and are suddenly and deeply constricted at the postorbital notch,
which follows immediately behind the orbits. Above the orbits the frontals
are broad and slightly concave, but they narrow rapidly towards the front
end. The postorbital process is very long and prominent, much more so
than in Protylopus, but this length is partly due to the great depth of the
postorbital constriction; the process is broad and heavy and bent downward,
so as to form a partial hinder boundary to the orbit, though the enclosure is
very far from complete. The supraorbital foramina are shifted much nearer to
the median line than in Protylopus, and broad, well-defined grooves lead for-
ward from them. No supraorbital notch is present. The nasals are long,
narrow, and slender, and are slightly convex both transversely and longitu-
dinally, but they are truncated in front and cease at the line of pt. In con-
sequence of this the anterior nares, though rather small, are much more
steeply inclined than in Protylopus, aud their oblique position suggests that
here we find the beginnings of the transformation which led to such remark-
able results in Proteceras. The premaxillaries have quite stout, though
depressed, horizontal rami, in which the incisors are inserted; the ascend-
ing rami, on the contrary, are very narrow, much more so than in Protylo-
pus, and seem not to reach the nasals, though this is difficult to determine
positively.

The maxillary is quite extraordinarily elongate, and forms much the

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56
greater part of the face; the alveolar portion is very low, but in front of the
orbit the body of the bone rises to considerable vertical height, though this
height diminishes steadily to the premaxillary suture. The large infraorbital
foramen opens above p2. The palatine processes of the maxillaries are long
and narrow, and slightly concave transversely ; a deep palatal notch separates
the hinder half of the alveolus of m# from the palatine bone. Along the
‘edentulous portion of the maxillary a low ridge marks the limits of the soft
palate. The palato-maxillary suture is not distinctly shown, but appears to
be opposite m2, and the posterior nares are placed quite far back, their front
margin being on a line with that of m*; this margin is somewhat. raised
and thickened and has two short median spines.

The zygomatic arch is long, despite the posterior position of the orbit,
horizontal in position, and decidedly stouter than in Protylopus. The squa-
mosal element of the arch is quite long and extends forward to the hinder
margin of the orbit; it merely overlaps the jugal and is not received into a
notch of the latter, as it is in Proty/opus. The jugal is deep vertically, laterally
compressed and elongate ; it has no distinct postorbital process.

The mandible is quite like that of Protylopus, but displays a number of
minor differences ; its horizontal ramus is long, shallow, and slender, though
rather stouter than in the latter, while the diastemata give it a somewhat
different appearance; the symphysis is shorter and the chin rather more
steeply inclined, though in Wortman’s specimen the symphysis is procum-
bent and almost horizontal. The difference may be specific or may be partly
due to crushing. Three mental foramina are visible, a large one beneath pj,
and two small ones beneath pz and p; respectively. The ascending ramus
of the mandible is broad and the angle is much extended behind the con-
dyle, quite as in Protylopus ; the masseteric fossa is placed high up, its lower
border being on a line with the molars. The condyle is transversely extended
and is raised relatively little above the level of the teeth; the coronoid process
is high, erect, and pointed, but not recurved, and therefore quite different from
the ruminant-like form seen in Protylopus.

The vertebral column, so far as it is preserved, is not especially peculiar ;
it is represented in specimen No. 11,223 by the atlas, axis, and four lumbars.
The atlas is quite elongate and seems to be rather narrow, though, as the
transverse processes are incomplete, the full breadth of the vertebra cannot
be determined. The neural and ventral arches are both strongly curved,

giving to the canal a somewhat circular outline; the neural arch bears a low

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57

but distinct spine, which arises near the anterior border. The anterior cotyles
are deeply concave and are quite widely separated, both dorsally and ventrally ;
they are notched quite deeply on the anterior border. The surfaces for the
axis are rather small and are placed very obliquely with reference to the me-
dian line. The vertebrarterial canal pierces the base of the transverse process
and runs but a brief course.

The axis has a moderately elongate, broad, and depressed centrum, which
bears a prominent keel upon its ventral face. The articular surfaces for the
atlas project outward prominently beyond the sides of the centrum, but their
principal diameter is the vertical one; deep notches separate the-dorsal por-
tions of these surfaces from the neural arch. The odontoid process is mod-
erately elongate, peg-shaped, and bluntly pointed, but is so broad and stout
as to suggest that it will eventually take on the spout-like form. The trans-
verse process is thin and compressed, but deep vertically, and is perforated
by a short vertebrarterial canal. The neural canal is narrow, but rather high,
and the pedicels of the arch are short from before backward. The neural
spine is quite remarkable, forming a large, hatchet-like plate; it is well
extended antero-posteriorly, especially behind the zygapophyses, and over-
hangs both the atlas and the third cervical, but is rather low vertically, and
has a strongly curved free margin.

The lumbar vertebree which have been preserved form a series of four,
probably the second, third, fourth, and fifth; they are large and strong, and
indicate considerable muscular power in the loins. The centra are long and
depressed, and the neural arches are low, but the transverse processes are
long, broad, and heavy, and they extend outward without much anterior cur-
vature, considerably resembling those of Protoceras.

Of the fore-limb the parts preserved are the distal end of the radius and
an imperfect manus, associated with the skull (No. 11,225); the distal end of
the humerus and the proximal end of the ulna and radius of the second
specimen (No. 11,223), which is referred, though with some little uncertainty,
to the same genus and species. The humeral trochlea is intermediate in
character between Protylopus and Protoreodon ; it is fairly high and cylindrical
_ in form, but is divided into three portions for the corresponding facets on the
head of the radius. Of these, the median or intercondylar portion is convex,
the others concave; the internal facet is considerably wider than the external.
The intercondylar ridge is much broader and more rounded than in Protylopus,

but less so than in the oreodonts. The external epicondyle is small, but the

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58

inner one is large, prominent, and rugose; it is not pushed so near to the
postero-internal angle as in the oreodonts, but retains an altogether internal
position. The anconeal fossa is quite deep and perforates the shaft at one
point, making a small supratrochlear foramen.

The bones of the fore-arm are not anchylosed at any point, at least in
the specimens before me, both of which belong to adult animals with com-
plete but unworn dentition. The ulna is represented only by a small part of
the proximal end, from which a great part of the olecranon has been broken
away. So far as it is preserved, it resembles that of Protylopus ; the olecranon
is thick and broad, agreeing in proportions with that of the latter, and, as in
that genus and in Poebrotherium, the process is continued upward in the line
of the shaft, not projecting back of it. Although the coronoid process is
prominent, yet the sigmoid notch is not very deep, for its distal portion is
not produced forward, the radius occupying the entire breadth of the humeral
trochlea. On the outer side, the facet for the humerus is confined to the
proximal portion of the sigmoid notch, but on the inner side it is continued
downward to the contact with the radius. For the latter there are two small
proximal facets, separated by a narrow sulcus. The proximal portion of the
shaft is stout and trihedral, with rounded posterior border; of the distal end
it can be said only that it is stouter than in Protylopus.

The proximal end of the radius is quite suggestive of that of the oreo-
donts. In correspondence with the form of the humeral trochlea, the head of
the radius is narrow, not much wider than the shaft; what little expansion
there is, is towards the ulnar side. The articular surface for the humerus is
divided into three clearly demarcated facets, the outer one nearly plane and
descending obliquely forward, the median one distinctly concave, and the
inner one narrower and saddle-shaped; the dorsal border is raised into a
point opposite the median concavity. Proximally, the shaft is narrow, but
quite thick and of transversely oval section; distally, the shaft is slender and
the distal end is very moderately expanded, covering the scaphoid and lunar,
but apparently not touching the pyramidal.

The manus (Plate IL, fig. 13) is but little differentiated, though not unlike
that of Protylopus. The carpus is in such a damaged condition that many
important questions regarding it must remain unanswered; it bears a general
resemblance to that of Leptomeryx, but differs in a number of details, especi-
ally in the height of the distal elements. The scaphoid is a large bone, high,

broad, and thick; distally it rests in almost equal proportions upon the trape-

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UINTA SELENODONTS 59

zoid and magnum, but is too much injured to show whether or not a trapezium
facet was originally present. The lunar is narrow, but quite high vertically
and rests almost equally upon the magnum and unciform, a very marked
difference from all known oreodonts; the junction of the two facets is at
such an angle as to make a sharp distal beak. Of the pyramidal only a
shapeless fragment remains. The trapezoid appears to be distinct from the
magnum, though this point is somewhat uncertain; it is very small. The
magnum is rather narrow, but quite high; its proximal end is divided sym-
metrically between the facets for the scaphoid and lunar, and distally it
appears to have a very limited contact with the second metacarpal. Of the
unciform it can be said only that it is broad and high, and carries a stout
hook upon the plantar face. The pisiform is short and stout, laterally com-
pressed, but deep vertically; at the free end it is moderately thickened and
incurved towards the radial side; its shape is very much as in Protylopus, but
somewhat shorter and heavier.

The metacarpus consists of four functional elements and has a general
resemblance to that of Protylopus, but differs from it in the more uniform
size of the bones, the median pair being less enlarged and the lateral pair
less reduced.

Metacarpal ii. is long, straight, and quite slender, though decidedly stouter
than in Protylopus ; the proximal end is enlarged in the dorso-palmar diameter,
but not transversely ; the head articulates by means of a concave facet with the
trapezoid and sends out a short process towards the ulnar side, which probably
reaches the magnum, though the state of preservation of the bones is not
sufficiently good to make this point clear. Below the proximal end the shaft
is of nearly uniform size and quite straight, though with a slight curvature
towards the ulnar side. The distal trochlea is low and small.

Metacarpal iii. is considerably longer than me. ii. and distinctly heavier,
though as compared with me. iii. in either Protylopus or Leptomerysx it is still
slender. The head has the usual transversely concave facet for the magnum,
and sends out a prominent process to meet the unciform, which process is
somewhat larger than in Protylopus, and beneath it the shaft is more excavated
for the head of me. iv. than in the latter. The shaft is straight and narrow,
but rather thick, while the distal trochlea is narrow and very low. As always
in these early selenodonts, the carina is entirely plantar in position.

Metacarpal iv. differs from me. iii. only in the shape of the proximal end,

which has but a single carpal articulation, that with the unciform.

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60

Metacarpal v. is like the second, except that it has a narrower proximal
end and a more strongly curved shaft. In correspondence with its larger size,
this bone has a more extended contact with the unciform than in Protylopus.

A single phalanx, the proximal one of the fourth digit, is preserved in
connection with the manus; it has the same general shape as in Protylopus, but
is depressed and very slender.

The pelvis (No. 11,223), so far as it is preserved, is tylopodan in character
and recalls that of Leptomeryx. The anterior portion of the ilium is broken,
so that its length cannot be determined, but it may be seen that the plate-
like expansion is broad and widens suddenly from the peduncle; the latter
is rather short and stout, having a considerable vertical diameter; the pubic
and acetabular borders are obscurely marked, and the iliac surface is narrow.
The ischium is relatively quite long, a marked difference from Poebrotherium,
in which this element is much shortened; it is, for the most part, narrow
and compressed, but rather deep dorso-ventrally and sub-trihedral in section ;
the dorsal border forms a thin and prominent crest above and for some dis-
tance behind the acetabulum, drooping suddenly at the ischiadic notch. The
hinder part of the ischium is expanded, depressed, everted, and plate-like ; no
tuberosity is preserved, but one may, nevertheless, have been present. The
acetabulum is large and deep and has very prominent borders, which project
far out from the sides of the pelvis. The pelvis of Protylopus, so far as it is
known, is similar to that of the present genus, but has a little more the aspect
of the innominate bone in Poebrotherium, while Leptoreodon agrees somewhat
more closely with Leptomeryx in this regard, though the four genera are very
much alike, so far as the pelvis is concerned.

Of the femur (No. 11,223) the proximal end is lost. The shaft is rel-
atively quite long and stout, especially in the antero-posterior dimension, and
is well arched forward. This arching is, however, less marked than in the
White River genera, Poebrothertum and Leptomeryx, but more than in the con-
temporary Protylopus. As in all the genera mentioned, there is a pit. above
the external condyle for the insertion of the plantaris muscle, a feature which
is absent in the modern Camelide, though in Poebrothertum it is deeper and
larger than in the Uinta genera. The rotular trochlea is narrow but promi-
nent, and is deeply grooved. The condyles are rather small and narrow and
of almost equal size; they are larger than in Protylopus and extend farther
behind the plane of the shaft, making the entire distal end thicker than in that

genus, for both condyles and trochlea are more prominent.

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61

The tibia (No. 11,223) is shorter, more slender, and in every way smaller
than that of Protylopus, from which it may immediately be distinguished
by the far less prominent development of the cnemial crest. The condyles
for the femur are narrow, but well extended from before backward, and of
nearly equal size. Despite their extension, these condyles do not project so far
back of the plane of the shaft as in Proty/opus. The proximal portion of the
shaft is stout and trihedral; beneath the cnemial crest it becomes much more
slender and assumes an oval section, expanding in both dimensions at the
distal end. As already mentioned, the cnemial process is far less conspicuous
than in /Pyotylopus, a difference which especially affects its antero-posterior
breadth, for in length there is little difference; distally, it dies away much less
abruptly upon the shaft. The distal end of the tibia exhibits no noteworthy
difference from that of the last-named genus, except that the malleolar process
is somewhat longer and heavier.

In none of the specimens is the fibula quite complete, but there can be no
doubt that it was uninterrupted and entirely free from the tibia. The proxi-
mal end is very narrow and compressed, though it has considerable antero-
posterior extension; the shaft is much reduced and very slender, and though
it has not attained the thread-like proportions found in Protylopus, yet it is far
more slender than in any of the known oreodonts. The distal end is a narrow
but thick external malleolus, which is deeply channelled on the outer side by
the sulcus for the peroneal tendons, and which has shifted partly beneath the
edge of the tibia. ;

The pes (Plate II., fig. 14) (No. 11,223) is of very considerable interest.
The tarsus is of the same structural type as in Protylopus, but may readily
be distinguished from the latter by the smaller proximo-distal height of its
members, especially of the cuboid. In size, shape, and general appearance
the astragalus resembles that of the last-named genus, with a few differ-
ences in relatively unimportant details. The tibial trochlea is quite deeply
grooved and somewhat more asymmetrical than in Protylopus, the outer
condyle exceeding the inner one more in width, thus bringing the deepest
part of the groove nearer to the internal side. On the distal trochlea the
cuboid facet is conspicuously narrow. The sustentacular facet is broad,
extending to the tibial border of the bone.

The calcaneum is relatively long and slender; its actual length is almost
the same as in Protylopus, and thus the bone is proportionately longer, as
compared with the rest of the limbs and feet. On the other hand, the tuber

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62

is somewhat shorter, a difference which is due to the position of the fibular
facet, and distinctly more slender, and the depression upon the external side,
while large and deep, is smaller and shallower than in the last-named genus.
The fibular facet is an elevated and regularly curved prominence, which is
placed somewhat more proximally than in Proty/opus, thus making the tuber
shorter and the distal portion longer relatively.

The cuboid shows no tendency to codssify with the navicular, and is
high and narrow, though distinctly less so than in Proty/opus ; the astragalar
facet is very narrow and simply concave in the dorso-plantar direction ; it
rises high above the calcaneal facet in a very characteristic way, forming a
tall, narrow prominence, the internal (tibial) border of which is bevelled to
provide for the expansion of the navicular proximally. The calcaneal facet
is very deeply incised and its dorsal margin is far below that of the navicular
facet. This constitutes a very marked difference from the condition seen in
Protylopus, and is correlated with the relatively greater length of that part of
the calcaneum which lies distal to the fibular facet. The calcaneal facet differs
further from that of Protylopus in lacking the expansion upon the plantar side,
which in the latter forms an overhanging shelf. The plantar hook is narrow
and bluntly pointed, very different from the massive ridge which is found in
Protylopus. The distal end of the cuboid is mostly taken up by the large facet
for the fourth metatarsal, but posterior to this is a very small one for the fifth.

The navicular is a large bone, exceeding the cuboid in every dimension
save the proximo-distal one; the proximal portion is expanded transversely at
the expense of the cuboid. The plantar hook is longer than in Protylopus, but
more slender and pointed. The distal face is occupied almost entirely by the
facet for the compound cuneiform; that for the internal one is very small and
placed at the postero-internal angle.

The ento-cuneiform is small and flat and lies in the concavity embraced
by the plantar hook of the navicular; distally it bears a small, concave facet,
which suggests that at least a vestige of the first metatarsal was preserved.

As in all the members of the present series from the Wasatch 7Jrigono-
lestes (Pantolestes) onward, the meso- and ecto-cuneiforms are firmly coossified,
but the shape of each element may still be distinguished. The meso-cunei-
form is very small and almost concealed when the pes is seen from the front,
while the ecto-cuneiform is very large and occupies nearly the entire breadth
of the navicular. This compound bone is quite like that of Protylopus, but is

shorter proximo-distally.

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UINTA SELENODONTS

The metatarsus is composed, so far as is definitely known, of four func-
tional elements, for though the lateral pair are considerably reduced and are
more slender than the corresponding metacarpals, they are far from being
thread-like splints, such as we find in Protylopus.

Metatarsal i. may, perhaps, have been preserved in the form of a ves-
tigial nodule, as is suggested by the facet on the distal end of the ento-
cuneiform.

Metatarsal ii. is quite long and very slender; it is longer in proportion to
the median pair than is the second metacarpal, and much more slender. But
it must be borne in mind that the manus and pes here described belong to
different individuals, possibly even to different genera, although the example
of Leptomeryx, Pretoceras, and Protylopus shows that such a difference in the
degree of reduction between the fore- and hind-foot is not of itself unlikely.
The head of mt. ii. is slightly widened and thickened, and its plantar edge is
bevelled for the ento-cuneiform ; the shaft is slender and nearly straight. The
distal trochlea is very narrow, but has a considerable dorso-plantar thickness
and bears a prominent carina.

Metatarsal iii. far exceeds mt. ti. in all of its dimensions, but is both
absolutely and relatively very much shorter than in Protylopus. It is consid-
erably longer and stouter than the corresponding metacarpal, though the
difference is less than in the last-named genus or in Leptomeryx. The proxi-
mal end is narrow, the shaft moderately long and stout, straight, and of nearly
uniform width throughout. For part of its length the shaft is trihedral, the
fibular side being flattened by its close approximation to mt. iv., assuming a
transversely oval section below. The distal trochlea resembles that of Proty-
lopus, being low and subspheroidal in shape rather than cylindrical; it is
demarcated from the shaft by a somewhat deeper depression than in the
latter genus.

Metatarsal iv. is slightly longer than mt. iii., its proximal and distal ends
standing at a little lower level than those of its fellow.

Metatarsal v. corresponds in length and thickness to mt. ii, but has a
somewhat heavier and larger proximal end.

Of the phalanges of the pes only a single one is preserved, a second
phalanx of one of the median digits; it closely resembles the corresponding
bone of Protylopus and is of nearly the same actual length. It is, therefore,
much longer in proportion to the length of the metapodials and decidedly
more slender.

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64
UINTA SELENODONTS
MEASUREMENTS.
No. 11,225
Length of face. : : - 0.057 Mandible, depth at mz : . 0.010
Forehead, width . c é esOSA: “ fo SSDS b ; -O12
Palate, length . a c geeZOOO
‘c= -widthsatm=: 5% we SOL7
Metacarpal i., length . f 72030 Metacarpal iv., length . : . 036
uf ‘« breadth, prox. end, .oo4 ig «breadth, prox. end,
a es a high. -003 te ag se diste iat -006
es il., length . > “ae OB 85 a v., length . d smn
ais «« breath, prox.end. .006 ig “breadth, prox.end, .0035
AG ce ay CiSES aN Sa OO5 5 se se ue dist. «« 005
No. 11,223
Tibia, length ; : F . 0.108 Metatarsal ii., length . : 7a OA4:
‘« breadth, proximal end ee OL eG ‘« breadth, prox. end, —.0025
«* thickness, oe : .021 ag oe oe Gist 2s -004
‘breadth, distal end . CeOl2 i ili., length . : epee O52
Fibula, thickness, ‘‘ : ; .008 GC Es breadth, prox. end, .006
Calcaneum, length P : 034 ue ae os dista. a .007
Astragalus, ‘‘ ; : eat Ol; es iv., length 3 2.053
as breadth, proximal end. —.007 Ke ‘« breadth, prox. end, .0045
a Ob distal 6-008 a6 s ug distm eck .006
Cuboid, length . : : + .009 é v., length . . Be hog}
co ewicthienee ° é . 005 Wg “breadth, prox.end . — .003
ss oe a dists 4, (a OOdis

The Systematic Position of Leptoreodon.

Wortman does not express himself very definitely upon this question.
In one place he speaks of “the Oreodonts other than Leftorcodon” (’98, p.
96, foot-note) and in another place he says: “ Upon the whole, I think it may
be safely concluded, from the evidence at hand, that Leptorcodon held the same
position with reference to the American Oreodontide that Xzphodon did to
the European Anoplotheritde.” (P. 97.)

I have reached a different conclusion. The phylogenetic position of this
genus is not so clear and definite as that of Protylopus, because we have as
yet found no White River genus which is so obviously descended from

it as Poebrotherium is from the former. Leaving aside for the present the

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UINTA SELENODONTS

oreodonts and agriocheerids, it seems highly probable that all the Uinta
selenodonts are closely related to one another, and there is no reason appar-
ent to doubt that they were all derived from the same family, possibly even
from the same genus, of Bridger times. The only important differences in
the dentition between Leptoreodon and Protylopus are as follows: In the for-
mer the upper canine is large and the lower canine has assumed the shape
and function of an incisor, while pz; is caniniform and takes its place. Con-
siderable diastemata separate the first from the second premolar in both jaws.
Except in very minor details, the other premolars and the molars are alike in
the two genera. We also find great similarity in the character of the skull,
although in Leftoreodon the face is longer and of greater vertical height, and
the mandible has in both the same great extension behind the condyle. In
both the feet and limbs are very much the same, save that in Protylopus the
metapodials are more elongate and the lateral digits, especially those of the
pes, far more reduced. Homacodon may serve as well for the Bridger ances-
tor of one genus as of the other.

Looking forward to White River times, the descendants of Leptoreodon
cannot be so distinctly identified, though it seems highly probable that one of
these is Protoceras. Unfortunately, there is a wide, unbridged gap in this line
between the Uinta and the upper White River, and unless the problematical
Stbarus should belong in this series we have yet to find the successive steps
that led up to Protoceras. he latter genus has in the structure of its skull a
number of deceptive resemblances to the higher Pecora, resemblances which
the rest of the skeleton does not sustain. Highly significant is the fact that
in the males the upper canine is a curved tusk, abraded upon the posterior
face by the caniniform py. Except that they have increased in size, the limbs
and feet show surprisingly little advance over those of Leptoreodon ; almost
the only changes to be noted are the reduction of the fibula and of the lateral
digits of the pes, with the partial anchylosis of the ulna and radius. Compar-
ing Protoceras with Leptoreodon, one is surprised to find that, in view of the
long time interval which separates them, they should differ so little. All the
facts, as we at present know them, point to the conclusion that Protoceras was
derived from Leftoreodon or from some very similar genus.

In my former paper upon the osteology of Protoceras I called attention
to the many points of resemblance between this genus on the one hand and
Leptomeryx and Hypertragulus on the other: “ This family represents a group
of White River selenodonts, each of whose genera has become more or less

5

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66

specialized in a way peculiar to itself, and with a tendency to simulate the
Pecora in some respect or other, yet always retaining a number of primitive
features. I cannot but believe that Protoceras represents a divergent offshoot
of the same stock, which, retaining in most respects the foot structure belong-
ing to the common ancestor of all these genera, has, at the same time, won-
derfully paralleled the higher Pecora in many features of the skull.” ('95d,
p- 365.)

The newly discovered material of Leptomeryx and Hypertragulus brings
out very clearly their tylopodan affinities and confirms Riutimeyer’s views
concerning them. If Leptoreodon be the ancestor of Protoceras, as there is so
much reason to believe, there is all the more reason to refer the latter to
the Tylopoda, for it would be difficult to assign any ground for making more
than a family distinction between the former and Protylopus, almost the only
important difference between them being in the character of the canine teeth.

In my preliminary paper I suggested that Leptorcodon was the forerunner
of Leptomeryx also (’98, p. 77), but since I have seen the specimens belong-
ing to the American Museum, especially the fine skull which has been
figured by Wortman, this view strikes me as less probable. The skull seems
a little too large and heavy, and the orbit to have been shifted too far back, to
belong to a forerunner of Leptomeryx. Nevertheless, the ancestor of the latter
must have been some closely similar form, possibly even a smaller species of
the same genus. However that may be, the significant fact remains that in
the Uinta all these lines, including the main tylopodan series, are seen con-
verging very nearly to a common term.

The relation of Leptoreodon to the oreodonts offers a somewhat difficult
problem. Its most striking resemblance to this family is to be found in the
canine teeth and the caniniform first lower premolar, but the example of Leféo-
meryx and Protoceras shows that this peculiar arrangement is not confined to
the oreodont family. Certain other resemblances to the latter family also
occur in the limbs, as in the shape of the humeral trochlea and head of the
radius, but the feet are of quite a different type and approximate rather to
those of Protylopus. I am, however, inclined to the opinion that the resem-
blances to the oreodonts are not accidental, but that they have a real signifi-
cance and tend to connect that family with the Tylopoda. The late Professor
Cope once said to me that he believed Pyotoceras to be allied to the oreo-
donts, though I am not aware that he published this view. It is of impor-

tance as indicating the resemblances, which, though masked, could not escape

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UINTA SELENODONTS 7

Cope’s keen observation, and as helping to unify the American selenodonts.
The oreodonts have already become established as a distinct family in Uinta
times, and not until we find their Bridger ancestors shall we be able definitely

to fix their taxonomic position.

Camelomeryx Scott.

PLATE III., Ficures 15-18.
Proc. Amer. Phil. Soc., xxxvil., p. 77-

This genus is very much like Leftoreodon, though it should, in my judg-
ment, be separated from it. The type of the genus is a fairly well preserved
skull without the mandible (Princeton Museum, No. 11,226), and I provision-
ally refer to it a specimen in the American Museum (No. 2070), which consists
of a cranium without teeth, ulna, radius, manus, pes, and other bones. The
latter may, perhaps, be referable to Oromeryx, though the published accounts
of that genus are so vague as in the absence of teeth to render identification
well-nigh impossible.

The dentition (Plate III, fig. 16) is of the same type as that of Leptoreodon,
from which it differs only in minor points. The formula is: 1?2, C1, P4, M3.

The upper incisors are small and apparently only two in number; they
are separated from each other by a short space, and quite a diastema inter-
venes between the lateral incisor and the canine. The crowns are very small,
antero-posteriorly compressed, and somewhat chisel-shaped, resembling those
of Leptoreodon marshi, but not the conical crowns of L. gracilis. The very
small amount of wear which the incisors have undergone, in comparison with
the other teeth, indicates that they were of little functional importance to the
animal.

The canine is of rather peculiar form; its crown is not very long, but is
quite broad antero-posteriorly, and, though compressed, is thick transversely ;
the edges are sharp and the end very bluntly pointed. What little abrasion
the crown shows is upon the posterior surface, from which we may infer that,
as in Leptoreodon, p; had become caniniform, and that the lower canine had
gone over to the series of incisors. This tooth is smaller than that of Lep-
toreodon, its fore-and-aft breadth being especially shorter, and it has not the
thickened anterior border and external grooving which characterize the latter
genus.

The first premolar follows the canine after a short interval, and is sepa-

rated from p? by a considerable diastema; it has a small, simple, conical, and

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68

much compressed crown, which is supported upon two fangs. It entirely
resembles the corresponding tooth of Leptoreodon, except that it is smaller, and
this difference may well be sexual rather than generic. The second premolar
is much larger than p?; its crown is low, elongate, compressed, and trench-
ant, ending in an acutely pointed apex, and of cordate shape in profile, like
the premolars of the oreodonts. It is perfectly simple, without basal or inter-
nal cusps, and is supported upon two roots. The third premolar is externally
very similar to p2, but is thicker transversely and is carried upon three fangs ;
it has a minute anterior basal cusp. This tooth has suffered so much wear
that I cannot determine whether it possessed a deuterocone; if so, it must
have been smaller than in Leptoreodon, for the breadth of the crown is notably
less than in that genus. -The fourth premolar is like that of Lepéoreodon,
except that the external crescent has a more concave outer face, and that the
cingulum is decidedly more prominent at the outer angles of the crown,
forming minute though distinct buttresses at the points where these are so
prominent in p* of Leptomeryx. On the whole, the upper premolars of

Camelomeryx differ from those of Lepéoreodon only in minute details.

MEASUREMENTS.

Upper dentition, length I-1 to M-3 ; ; é : . 0,062
canine, antero-posterior diameter : 9 . Pe OOS
transverse diameter . : : ; é 1) 3003
premolar-molar series, length : ; : . a OSL
premolar series, length c : : é 2 Se eOZO
molar series, length . . : : : ‘ se 02)
M-1, length : F : : : ‘ F ; -0055
M-1, width : : ‘ ‘ ‘ , : é :0075
M-2, length , : ; : : : : ; .007
M-2, width : 5 ‘ ; ; ; 3 : .O10
M-3, length . : : : : : . SE OOSS,
M-3, width : : : : : ; ‘ a BOM

The upper molars also closely resemble those of the last-named genus in
their shape and proportions, but differ slightly in a few details of construction.
They increase in size, especially in width, from the first to the third, and have
quadrate outlines, forming transversely placed rectangles, though a slight
degree of asymmetry is produced by the somewhat greater breadth of the
anterior half of the crown, a difference which is most marked in m?. The

first molar, the smallest of the series, is so much worn that its pattern is

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UINTA SELENODONTS

almost completely obliterated. The second is also much abraded, making an
exact comparison with Lepftoreodon difficult, but it is obvious that the external
median buttress is distinctly larger than in the latter. The third molar may
be fully compared with that of the allied genus, which it resembles closely,
but differs in the larger size of the external buttresses, especially of the
median and posterior ones, which are very small in Leptoreodon ; the ribs
upon the outer crescents are also more prominent than in the latter. It is
interesting to observe that these differences are in the direction of Lefto-
meryx. From Protylopus the two allied genera differ in the greater breadth
of the upper molars.

The skull (Plate III, fig. 15) in its general character closely resembles
that of Leptoreodon and less nearly that of Protylopus, but has some well-
defined peculiarities of its own. It has the characteristic tylopodan form
which recurs so often among these Uinta genera and which is so well shown
in Protylopus, Leptoreodon, Leptomeryx, Hypertragulus, and even in Protoceras.
The cranium, measured from the occipital condyles to the anterior border of
the orbit, is considerably longer than the facial region, though the brain-case
proper is rather short and quite slender. Its narrowness and the great depth
of the postorbital constriction are in decided contrast to the conditions found
in Leptoreodon and Protylopus, in which the brain-case is broader and the
postorbital notches shallower. In similar contrast to the two genera men-
tioned is the sagittal crest, which is high and prominent, and which occupies
the entire length of the parietals, the temporal ridges being short and con-
fined to the frontals, where they pursue a nearly transverse course, instead of
converging gradually into the sagittal crest, as they do in Lefttoreodon and
Protylopus, The forehead is broad over the orbits, ceasing abruptly behind,
but contracting gradually in front into the narrow, rounded muzzle. The
orbit is quite small and has an anterior position, its front margin lying above
the middle of m1, almost the same position that it occupies in Leptomeryx.

In Leptoreodon the orbit is larger and not so far forward, and in Protylopus
also it has shifted backward, in consequence of which the muzzle is as long as
in Camelomeryx, despite the fact that Protylopus is without diastemata.

The occiput is small and low, broad at the base, but contracting rapidly
towards the summit; its shape is as in Leptomeryx, but it is actually and
relatively lower and narrower. The basioccipital is quite elongate and very
broad proportionately ; its ventral surface is nearly flat, but is broken near

the anterior end by two low eminences, between which is a broad, shal-

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7O

low groove. In Lepfomeryx this bone is as long and quite as broad, but
appears to be narrower because of the convexity of its ventral surface. The
exoccipitals are low and wide, narrowing dorsally; as in Protylopus, they
form a broad prominence above the foramen magnum, with a fossa on each
side of it; the condyles are quite large, expanded laterally, but depressed
vertically; in the median ventral line they are separated by a broad, shal-
low notch. The paroccipital processes are laterally compressed and broader
than in Protylopus, but, as in that genus, they stand well in advance of the
condyles, enclosing large fossz with them. In Leptomeryx the processes
have the same shape as in Camelomeryx, but are somewhat smaller and
placed farther back. The supraoccipital would seem to have resembled that
of Leptomeryx and to have had about the same extension upon the roof of
the cranium; the lambdoidal crest is quite prominent in both genera. A
considerable strip of the periotic is exposed between the exoccipital and
squamosal, but does not give rise to any distinct mastoid process.

The basisphenoid resembles the basioccipital in shape, save that it is
somewhat narrower. The alisphenoid is quite large; its ascending process
forms a considerable portion of the floor of the cerebral fossa, rising in front
to make part of its anterior wall. This bone is so exactly like that of Lepto-
meryx in shape that I may apply to it the description elsewhere given of the
latter: ‘“‘The alisphenoid is directed nearly horizontally, but there is a
curious angulation or ridge in it, from which a portion of the bone passes
upward, bounding the anterior edge of the temporo-sphenoidal lobe of the
cerebrum.” (’gIc, p. 346.) However, in Leptomeryx this angulation is slightly
more pronounced. In none of the specimens is the tympanic preserved, and
the periotic is thus exposed to view; the fossa shows, however, that the bulla
must have been very small, smaller even than in Leptomeryx, and the con-
tracted space between the postglenoid and posttympanic processes of the
squamosal indicates an auditory meatus of small size, much smaller than in
Protylopus.

The parietals are very long and narrow, forming almost the entire roof of
the cerebral fossa. For their entire length they unite to form a thin but promi-
nent sagittal crest, which is far longer than in Leptomeryx, in which the tem-
poral ridges are continued over upon the parietals, thus shortening the crest.
In this respect both Leptoreodon and Protylopus are more like the White River
genus. The parietals are even longer and narrower than in Leptomeryx, and

differ from those of the latter in not diverging anteriorly to receive the

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UINTA SELENODONTS 7

median prolongations of the frontals; the narrowness of these bones is due
both to the slenderness of the cranium and to the large size of the squa-
mosals.

The squamosal is a very large bone, both longitudinally and vertically,
and makes up the greater part of the cranial side-wall; it is highest behind,
its suture with the parietal running quite steeply downward and forward.
The posttympanic process is short, but quite thick, and is made conspicuous

_by its separation from the paroccipital; the notch between the posttympanic
and postglenoid processes is narrower than in Leptomeryx or Protylopus. The
root of the zygomatic process forms a much narrower and more horizontally
directed shelf than in the White River genus, and the glenoid cavity is of
quite a different form. In Leptomeryx the articular surface is larger and nearly
flat or slightly convex; from the external side it is invaded by a large, deep
concavity, which is visible as a broad sulcus when the skull is seen in lateral
view, and which intervenes between the articular surface and the postglenoid
process; internally the two are continuous. In Camelomeryx the surface is
broad and simply convex, and only a slight indication of the external sulcus
is visible ; the postglenoid process is high, broad and thick, even larger than
in Protylopus, and much larger than in Leptomeryx. The zygomatic process is
broken away, but the form of the jugal shows it to have been longer than in
the last-named genus.

The jugal is long, quite heavy in front, especially in the vertical dimen-
sion, and tapering posteriorly ; it is largely expanded upon the face, both in
front of and beneath the orbit ; the masseteric surface is broad and distinct
and is bounded by a prominent masseteric ridge; the postorbital process is
exceedingly small and is widely separated from that of the frontal. This jugal
differs in several important respects from that of Leptomeryx, it is longer,
shallower vertically, but thicker and less plate-like; the masseteric surface
and ridge are much better developed and the postorbital process much
smaller, leaving the orbit far more widely open behind; the inferior boun-
dary is flat and not flared out into a prominent lip, as it is in the White
River genus. As a whole, the zygomatic arch is longer than in the latter,
both because the glenoid cavity is farther behind the molar series and because
the orbit does not extend so far back. In both genera the anterior boundary
of the orbit occupies the same position, above m+, but in Leptomeryx the
orbit is larger and its hinder margin is well behind the molars, while in the

Uinta genus it extends only to the posterior edge of m2.

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72

It is impossible to make out the limits of the lachrymal, or to determine
whether a vacuity was present between it and the frontal.

The frontals are relatively very large bones; they are both long and
broad, but take almost no share in the formation of the cranial roof, for they
cease abruptly at the line of the postorbital processes. The temporal ridges
thus follow an almost straight transverse course, curving backward very
slightly as they approach the median line. The forehead is broad and tri-
angular, contracting anteriorly; it is almost flat, or slightly concave, with a
prominent median ridge. The postorbital processes, properly so called, are
not very long and but little decurved, but they have the effect of great length,
because the forehead and orbits project out widely beyond the sides of the
narrow cranium, which is in marked contrast to the condition found in Proty-
fopus and much more extreme than that in Lepftoreodon. In Leptomeryx a
remnant of the same condition may be observed, but the broader and more
capacious cranium renders it much less conspicuous.

The nasals are long, narrow, and convex, slightly so in the longitudinal
direction, and strongly so in the transverse. For most of their length they
remain of nearly uniform width, and in front their emarginate tips project
freely for a short distance beyond the premaxillea. So far as they are pre-
served, these nasals agree very well in shape with those of Leptomeryx, but
probably do not extend so near to the orbits.

The premaxillaries are evidently in a state of incipient reduction; the
alveolar portion is very low and short, shorter than in Leptoreodon and much
shorter than in Protyopus, and the ascending ramus forms, when seen from
the side, a narrow strip along the front of the maxilla, widening a little at the
nasal suture. Transversely, however, the ascending ramus is quite broad
and contracts the narial opening considerably. This opening is very small,
terminal, and nearly erect in position. The palatine processes are small and
the incisive foramina narrow. In Leptomeryx the premaxillary has an ascend-
ing ramus which is considerably broader (antero-posteriorly) than in the
Uinta type, but transversely is very thin and compressed.

The maxillary is long and low, especially beneath the orbit, and even in
front of the latter the facial portion is lower than in Leptomeryx and the
edentulous region is decidedly shorter. The muzzle tapers anteriorly and is
constricted in front of p2, but is expanded again by the swollen alveoli of the
large canines. The palatine processes are long, somewhat concave trans-

versely, and almost plane longitudinally. The bony palate is of nearly uniform

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NI
ios)

width throughout, because the inner or lingual borders of the premolars
and molars are arranged in almost the same fore-and-aft lines, those of the
two sides keeping nearly parallel. However, the total breadth of the skull,
measured to the outer sides of the teeth, is far greater at m® than at pl. The
palate is narrowed in front of p2, but broadens again slightly at p! and still
more at the canines. Anteriorly the palatine plates diverge widely to receive
the premanillary spines. The posterior nares are not preserved in either of
the available specimens, but enough is left to show that the opening must
have been farther back than in Lepéoreedon, and that the palatal notch, which
is quite distinct in the latter, is hardly at all indicated. This character of the
palate forms another approximation to the structure of Leptomeryx.

Comparatively few of the cranial foramina are exposed to view. The
condylar foramen is large and is placed in the angle between the condyle and
the horizontal portion of the basioccipital; external to it is a second small
foramen. The foramen lacerum posterius is a narrow, curved slit, which
bends around the periotic and is continued anteriorly into the foramen
lacerum anterius, though the bulla probably separated them when it was
present. A large glenoid foramen makes a conspicuous opening upon the
hinder face of the postglenoid process. As in Leptomeryx, the foramen
rotundum is separate from the foramen lacerum anterius and is placed near
the foramen ovale, internal to the glenoid cavity. A small venous foramen
perforates the bony palate on each side, opposite p!. The infraorbital fora-
men, which is quite large, occupies the same position as in Leptomeryx,
opening above p” and well in advance of the orbit. I can detect_no supra-
orbital foramen, but the frontal is not sufficiently complete in either of the
Specimens to enable me to say definitely that it was lacking. If present,
however, it must have held a very different position from that of Leptorcodon,
farther forward and much nearer to the median line; the absence of vascular
grooves on the forehead is a marked distinction from Leptoreodon and Oro-
meryx, In Leptomeryx the supraorbital foramen is a minute paired opening
placed near the outer rim of the frontal.

In the collection of the American Museum of Natural History is a speci-
men (No. 2070) which apparently belongs to this genus, though in the un-
fortunate absence of upper teeth the reference must remain somewhat uncertain.
The cranium agrees exactly both in size and in character with that of the
type specimen, and this agreement is the principal reason for referring the
fossil to Camelomeryx.

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74 UINTA SELENODONTS

The ulna and radius are long and slender and seem to be firmly coossi-
fied, though it is difficult to determine this point. At all events, they are very
closely approximated throughout their length and are anchylosed at points,
but, at the same time, their limits are clearly shown by deep grooves along
the line of junction. The radius is relatively well developed; its proximal end
is moderately widened, but thin and compressed antero-posteriorly, and in
shape resembles that of Leptomeryx. The humeral surface is divided into
two facets of unequal size, the internal one being considerably the larger; the
groove for the intercondylar ridge is shallow, but makes a distinct notch on
the dorsal border of the proximal end. The shaft is long and quite broad
transversely, with a well-marked curvature towards the anterior side. In
general proportions it is very different from the slender, cylindrical form
which is characteristic of the oreodonts and rather resembles that of Lepto-
meryx, but is of less uniform width than in the latter; it is widest proximally,
gradually contracting towards the middle, whence it again expands towards
the distal end. The latter is moderately broad and thick, and displays a broad
and shallow sulcus for the extensor tendons upon its anterior face. The facets
for the scaphoid and lunar are of nearly equal size, though the former is
slightly the larger; it is also reflected farther up upon the palmar face; the
lunar face is simply concave.

Despite its anchylosis with the radius, the ulna is quite stout and very
little reduced. The olecranon is so broken that its exact size and shape can-
not be determined, but it was evidently large and heavy. The sigmoid notch
is rather shallow, though the coronoid process is prominent, and the humeral
facet is almost confined to the inner side; the external radial facet forms a
marked projection. The shaft is quite stout, especially its proximal third,
tapering steadily towards the distal end; the inferior part is laterally com-
pressed and plate-like. The distal end is somewhat thickened, but its internal
side is deeply notched to receive a projection from the radius. The facet for
the pyramidal is small and saddle-shaped, and that for the pisiform, which is
quite small, is continuous with it. In Leptomeryx the ulna and radius are, in
general, much like those of the present genus, but they show no tendency to

anchylosis, though the shaft of the ulna is much more slender.

MEASUREMENTS.
Radius, length ; : C . 0.067 | Ulna, length . ; : : . 20.080
width of proximal end . .008 | ‘ width of proximal end . 7-006)

of distalend . 5 caper | “« of distal end : . 004

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75

The manus (Plate IIL, fig. 17) bears a close general resemblance to that
of Leptomeryx both in size and appearance, save that the lateral digits are
much less reduced. The carpus is broad and rather low, although the distal
elements are not so much shortened as they are in the White River genus.
The scaphoid is of only moderate size, low, broad, but rather thin in the dorso-
palmar dimension, and, except that it is somewhat thinner, it resembles that
of Protylopus. The distal end is divided somewhat unequally between the
facets for the trapezoid and magnum, the former rather the larger of the two.
Although the trapezium was probably present, no distinct facet for it is visible
upon the scaphoid.

The lunar is quite high and narrow, though less so than in Leptomeryx ;
the proximal end is not so much expanded transversely as in the latter, not
sending out such a prolongation towards the pyramidal; the distal end is a
wedge-shaped beak, formed by the junction of the magnum and unciform
facets, which meet at nearly a right angle, and of which the former is slightly
the larger. This symmetry of articulation between the lunar and the distal
bones of the carpus is somewhat exceptional in this group. In Protylopus
the unciform facet is larger than that for the magnum, while in Leptomeryx
the lunar rests almost entirely upon the unciform and has only a lateral con-
tact with the magnum, as is also true of all the oreodonts, even of Protoreodon.
In Protoceras, however, there is only a slight tendency towards this displace-
ment and the two facets are not far from equal in size, though that for the
unciform is a little larger and more distal.

The pyramidal is a relatively large bone, slightly exceeding the scaph-
oid in all its dimensions except in breadth. On its palmar side is developed a
large and prominent rugosity, such as is but feebly indicated upon the scaph-
oid. Of course, the large size of the pyramidal is to be correlated with the
stoutness of the ulna, and forms a decided contrast to the reduced pyramidal
of Leptomeryx. The ulnar facet is a transverse groove, with dorsal border
much elevated at the radial side, but descending steeply towards the ulnar
side; the pisiform facet is small and separated by a distinct ridge from the
ulnar surface, with which it forms nearly a right angle. Articulation with
the lunar, so far as the dorsal side is concerned, is by means of two facets,
proximal and distal, with a sulcus between them. A simply concave facet for
the unciform occupies the entire distal end.

The pisiform is smaller than in Protylopus or Leptoreodon and of a differ-

ent shape; its proximal end is transversely extended, which is unusual among

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the artiodactyls, and bears narrow, concave facets for the ulna and pyramidal.
The body of the bone is compressed, of moderate vertical depth, and so curved
that it presents a convexity towards the ulnar side, while the distal end is
slightly thickened. In the other Uinta genera above mentioned the pisiform
is much larger; it is not transversely extended at the proximal end, and is
much more thickened and club-shaped at the distal end. In Protoreodon this
bone is much broader than in Camelomeryx. The pisiform of Leptomeryx is,
unfortunately, not known, which prevents a comparison with that genus.

The trapezium is not preserved in connection with the specimen, but no
reason is apparent to doubt that it was originally present, as is indicated by
a small facet upon the radial side of the trapezoid. As in all of the Uinta
selenodonts whose carpal structure is known, the trapezoid is distinct from
the magnum. Leptomeryx is quite exceptional as a member of the Tylopoda
in having these elements united; the union does not occur in Profoceras or
Poebrotherium, or in the existing camels and llamas, though it is usual in the
Pecora and Tragulina. In Camelomeryx the trapezoid is quite a small bone,
though relatively high in the proximo-distal diameter, exceeding in this re-
spect the corresponding element of Leptomeryx. The proximal end is rounded
and convex, fitting into the concave facet upon the distal end of the scaphoid.
On the radial side is a small facet which was doubtless destined for articulation
with the missing trapezium. Connection with the magnum is maintained by
two facets, proximal and distal. The distal end, so far as may be judged from
the specimen, appears to bear an almost plane facet for the second metacarpal.

The magnum is still quite small proportionately, for the obvious reason
that the third metacarpal is not greatly enlarged nor the lateral digits much
reduced. The proximal end is unequally divided between the surfaces for the
scaphoid and lunar, which meet at a very open angle; the former is some-
what the larger and more completely proximal in position, while the lunar
facet is more oblique. A very small facet occurs at the disto-internal angle
for the head of the second metacarpal, which preserves its primitive connec-
tion with the magnum. Nearly all of the distal end is taken up by the large
facet for me. iii., which is only slightly convex. It is impossible to say defi-
nitely whether there is any dorsal contact between the magnum and the
unciform ; if so, it must have been very small, owing to the distal extension
of the beak of the lunar. In Leftomeryx the magnum is much lower proximo-
distally than in the present genus, and has so shifted that dorsally it lies alto-

gether beneath the scaphoid, as is also the case in Protoreodon. In Protylopus

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77

the magnum is relatively larger than in Camelomeryx and has a proportion-
ately larger scaphoid surface, though that for the lunar is still well developed,
and the distal surface for the third metacarpal is much more strongly convex
in the transverse direction.

The unciform is relatively small, hardly exceeding the scaphoid and
pyramidal in size, though in the vertical dimension it, like the other distal
elements, considerably exceeds the corresponding bone of Leptomeryx. The
lunar facet is small and oblique in position and makes an obtuse angle with
the surface for the pyramidal, which is altogether proximal. Quite a large
facet for the unciform process of the third metacarpal occupies the distal half
of the radial side and almost meets the lunar facet, leaving between them
only a very narrow area, which may come into contact with the magnum.
The distal end is but slightly convex, and the facets for the fourth and fifth
metacarpals lie in almost the same transverse plane. In Leptomeryx the unci-
form is broader and much lower; its surface for the lunar is more proximal in
position and its connection with the third metacarpal is considerably reduced.
In Protylopus the unciform is larger in every dimension than in Camelomeryx.
The proportions of its various facets are not markedly different from those of
the latter, except that the surface for the fourth metacarpal has somewhat
increased at the expense of that for the fifth.

In the specimen before us the metacarpus has preserved but four mem-
bers, but there is some reason to believe that five were present in the animal,
though doubtless the pollex was in a rudimentary condition. The median
pair of metacarpals are but moderately enlarged, while the lateral pair are but
slightly reduced, giving to the manus an almost isodactyl appearance. The
laterals are relatively little heavier, though decidedly longer than those of
Leptoreodon, and are, consequently, much less reduced than those of Protylopus.
In spite of its primitive appearance the manus of Cammelomeryx bears a dis-
tinct resemblance to that of Leptomeryx, although in the latter the lateral
metacarpals are very slender and almost splint-like. Metacarpal ii. is quite
long and stout, though shorter and more slender than the median pair; the
proximal end is not enlarged, except slightly in the dorso-palmar dimension,
its breadth not exceeding that of the shaft, and it bears a narrow, plane facet
for the trapezoid and a very minute one for the magnum. On the radial side
the head is flattened and slightly excavated, doubtless for the reception of
the rudimentary first metacarpal. For most of its length the shaft is closely
applied to that of me. ili, and is of uniform size and trihedral shape; its

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78

course is nearly straight, except for a slight eversion of the distal end.
Near the distal end the shaft is slightly contracted, becoming more rounded
in shape, but expands again just above the trochlea. The latter is sub-
spheroidal in shape and has quite a prominent palmar carina; it is demarcated
from the shaft by a narrow but distinct groove.

Metacarpal iii. considerably exceeds the second both in length and thick-
ness, though not so much as is usual among the selenodonts, even of this early
period. Except for the projection which abuts against the unciform, the head
is not expanded and is no broader than the shaft, and even this projection,
though it has quite an extensive contact with the unciform, reaches but slightly
across the head of mc. iv. There is, of course, no articulation with the trape-
zoid, which is prevented by the articulation, small as that is, of me. ii. with the
magnum. The facet for the magnum is almost plane transversely, as it also is
in Leptorcodon, while in Protylopus this surface is quite deeply concave. The
tubercle for the attachment of the extensor carpi radialis muscle is larger and
more rugose, though not more prominent than in the last-named genera. The
shaft is straight and of almost uniform diameter throughout, though broaden-
ing slightly above the distal trochlea, and for the greater part of its length the
dorsal surface is rounded and convex. The trochlea is low, of subcylindrical
form, and the carina is altogether palmar in position.

Metacarpal iv. differs in a few details from me. ill. It is a little shorter,
for the proximal end does not rise so high, owing to the downward extension
of the unciform; distally also it ends at a level slightly above that of mc. iti.
The head, which articulates only with the unciform, is, of course, differently
shaped, and the dorsal surface of the shaft is plane or very faintly concave,
instead of convex. The distal trochlea also is rather more spheroidal than

that of me. ili.
MEASUREMENTS.

Carpus, breadth . 3 5 27 OSLO Me. iii., breadth, distal end . - 0.006
height in median line . .0065 | Mc.iv., length . : : : -0345

Mc. ii., length . : : O33 breadth, proximalend . .005
breadth, proximalend . .0035 os oy distal end . . 0045

distal end . - 005 Mc. v., length . : 5 : -030
Mc. iii., length . : 5 ; .037 breadth, proximalend . .0035
breadth, proximalend . 005 | “ 6 distal end . - 0035

Metacarpal v. is slightly shorter and more slender than me. 1i., of which

it forms the counterpart. The head, which articulates by a good-sized facet

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UINTA SELENODONTS 79

with the unciform, is slightly enlarged and thickened; this is principally due
to the tubercle for the insertion of the extensor carpi ulnaris muscle. The
shaft is slender, laterally compressed, and almost straight, though displaying
a slight lateral curvature.

No phalanges have been found in connection with the manus.

Of the tarsus (Plate III., fig. 18) only the astragalus, calcaneum, and
cuboid are preserved, but these are sufficient for a satisfactory comparison
with the tarsus of the other Uinta genera. The astragalus is very much like
that of Protylopus, though a little smaller in actual size and somewhat broader
and shorter proportionately. The proximal trochlea is very asymmetrical, the
external condyle exceeding the internal even more than in Protylopus, while
the deep intercondylar groove is somewhat broader and more open than in
that genus. Both of these condyles, and especially the inner one, are rather
more widely separated from the distal facets for the cuboid and navicular re-
spectively. The various facets for the calcaneum, so far as they can be made
out, do not differ in any important respect from those on the astragalus of Pro-
tylopus, save that the surface for the sustentaculum appears to be hardly so
wide in proportion. The distal trochlea is very unequally divided between the
facets for the cuboid and navicular; the relative breadth of the two facets is
about as in Protylopus, but that for the navicular is of different shape, in that its
convex portion is rather narrower. The whole distal trochlea lies somewhat
internal to the proximal one, and this gives an oblique shape to the entire
bone. In Leffomeryx the astragalus is suggestively like that of Camelomeryx,
but exhibits a number of advances. Owing to the increased size of the in-
ternal condyle, the proximal trochlea is less asymmetrical and the intercon-
dylar groove is wider; the shape of the bone is less oblique, the proximal and
distal trochleee being more nearly in line, and the cuboidal facet is distinctly
broader, while the dorso-plantar diameter of the whole bone is increased.
Leptoreodon has an astragalus almost exactly like that of Camelomeryx, but is
a little longer and narrower, and the distal trochlea has a somewhat different
shape, due to the shallowness of the concave portion of the navicular facet.
In Protorecodon the astragalus is of the same general type, but is heavier and
more oblique in shape, with more asymmetrical proximal trochlea and more
rounded angles.

The calcaneum is a rather small and slender bone, with perhaps a
greater resemblance to that of Leptomeryx than to the corresponding tarsal

in the other genera which have been mentioned. The tuber calcis is quite

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80

short, narrow transversely, and thin in the dorso-plantar dimension, much as
in Leptomeryx, except that in the latter genus the tuber is distinctly elongate.
Upon the external side of the calcaneum, and running for most of its length,
is a very conspicuous sulcus, broad and deep; this sulcus is most marked in
Protylopus, less so in Leptoreodon, and still less in Camelomeryx, while in
Leptomeryx it is obsolete, only a slight remnant of it indicating that this
genus was probably derived from an ancestor which possessed it. The
fibular facet is narrow and does not rise so high as in Protylopus or Lep-
toreodon, but is more prominent than in Leptomeryx. The distal end of the
calcaneum is like that of the latter genus in having a considerable dorso-
plantar diameter, this diameter being ‘suddenly diminished just above the
fibular facet, as it is not in either Leptoreodon or Protylopus. The cuboid
facet is relatively broader, but less extended planto-dorsally than in the last-
’ named genus, in which the facet is so warped that its plantar portion presents
inwardly rather than distally, while in Camzelomeryx this warping is much less
in degree. From Leptomeryx the chief difference lies in the relative width of
the facet, the astragalus not taking up so much of the cuboid as in the White
River genus. The sustentaculum is much more prominent than in the oreo-
donts.

The cuboid is rather small, narrow, and light. The proximal end is
divided almost equally between the facets for the calcaneum and astragalus,
though the former is perhaps slightly the broader of the two, but not so
much so asin Protylopus or Leptoreodon, while in Leptomeryx the astragalar
surface is distinctly the broader one. The facets are shaped much as in
Protylopus, except that the cuboidal one is less warped and projects less
towards the fibular side. The plantar hook is quite large and heavy, but
far less so than in the last-named genus or even than in Leptoreodon, though
larger and heavier than in Leptomeryx. The distal end is entirely occupied
by the large facet for the fourth metatarsal, which is plane in front, concave
behind. It is doubtful whether any facet for the fifth metatarsal is present;
if so, it is exceedingly small. In Leptomeryx the cuboid is coossified with
the navicular, a feature which, like the anchylosis of the trapezoid and mag-
num, is very exceptional among the Tylopoda and has not been observed in
any Uinta genus.

The metatarsus consists of a large median pair and a very reduced lateral
pair, but as the latter are not preserved in connection with the specimen, it is

quite uncertain whether they were retained in their entire length or only

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8I

as short splints, though the former alternative seems the more probable one.
Metatarsal iii. is long and quite stout, much shorter, however, than in Proty-
Zopus and heavier than in Leptoreodon. The proximal end is narrow, but is
given considerable dorso-plantar extension by the large projection from the
plantar side. On the tibial side of the head is a shallow groove for the
reception of mt. ii. From the size and shape of this groove it is evident that
the missing metatarsal was exceedingly small. On the fibular side is a round
pit which receives a projection from mt. iv. The shaft is long, stout, and
nearly straight; it is broad transversely, but compressed antero-posteriorly,
except in the proximal portion, which is quite thick in the dorso-plantar
dimension; in breadth the shaft increases gradually and uniformly towards
the distal end. The distal trochlea is demarcated from the shaft by a very
distinct pit; the carina is but moderately developed and hardly at all visible
from the front. The shape of the trochlea shown in the drawing (Plate IIL,
fig. 18) is probably due to the crushing which the fossil has undergone.
Metatarsal iv. differs but slightly from mt. iii., except that the shaft is a
little broader. The head is narrow and the shaft widens gradually to the
distal end; the plantar projection is rather small, decidedly smaller than in
Protylopus, and the depression on the fibular side which receives mt. v. is even
shorter and shallower than the groove on mt. iii. for mt. ii. In Leptomeryx
the median metatarsals have coalesced to form a cannon-bone, while the lateral

pair are reduced to short splints, which are also anchylosed with the cannon-

bone.
MEASUREMENTS.

Astragalus, length . : : . 0.016 Metatarsal iv., width, proximal end 0.0055
width, proximaltrochlea .008 on OG distalend . .0085

OG «© distal trochlea . .008 Phalanx 1, length . 0 . 2 O18
Calcaneum, length (est.) f 5 AOR i width, proximal end . .006
Cuboid, height . : ; 7 OLS vs «« distal end . . .0045
OG width 3 : 5 - .006 Phalanx 2, length e 3 Od
sie thickness é : OLA ac width, proximalend . .0055
Metatarsal iii., width, proximal end .0055 ue «« distal end . ae OOd
ve ss distalend . .0065 | Ungual phalanx, length : 3» -O105
Metatarsal iv., length . : O52 fe Gi width proximalend .005 :

_ The phalanges are very much like those of Proty/opus, except that they
are relatively longer and more slender. As compared with the length of the

metatarsals, the proximal phalanx is very long and slender; its proximal
6

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82

trochlea is narrow and quite deeply concave; the body of the bone is elongate
and very narrow, and the distal trochlea is almost confined to the plantar face.
The second phalanx is very much shorter than the first and even more slender;
its distal trochlea is reflected well over upon the dorsal face. The ungual is
long, narrow, straight, and pointed. The phalanges of Lepfomeryx are of simi-

lar type, but a little shorter and thicker proportionately.

The Phylogenetic Position of Camelomeryx.

The problem concerning the taxonomic position of this genus is rendered
somewhat obscure by the incompleteness of our knowledge of it; the mandi-
ble and the inferior dentition are quite unknown, and the limbs and feet have
not yet been certainly identified, though there is every reason to believe that
the specimen above described represents very nearly the actual structure of
the genus. From the foregoing description it will be sufficiently obvious that
Camelomeryx is very closely allied to Leptoreodon, so much so that one can-
not but feel some doubt as to the propriety of separating them generically,
though if we may assume that the feet described in this and the preceding
section have been correctly referred, the difference is enough for generic dis-
tinction. It is a significant fact that almost all the minor differences which
separate Cameclomeryx from Leptoreodon are structural features in which the
former agrees with Leptomeryx, and suggest that the latter was derived from
it. There are, however, some objections to this view. In the first place, the
ulna and radius—which in the White River genus, are separate—are already
coossified in the Uinta form. This may be merely individual and due to
advanced age, or it may be specific, occurring only in C. /ongiceps, and again
the specimen may perhaps be properly referable to some other genus. But
if future research shall show that Camelomeryx is characterized by anchylosis
of the fore-arm bones, it will undoubtedly militate against the conclusion that
Leptomeryx was descended from it. Secondly, Leptomeryx is remarkable for
the character of its carpus, the magnum having shifted from beneath the
lunar, which rests entirely upon the unciform. We might reasonably expect
to find in the Uinta ancestor of this genus some indication of this displace-
ment, if only in the incipient stage, but in the carpus referred to Camelomeryx
there is no such indication.

Whether Camelomeryx be the direct ancestor of Leptomeryx or not, it is

highly probable that it very closely resembles that ancestor in all save a few

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minor details of structure. At all events, we may feel confident that in the
group of Uinta selenodonts represented by Camelomeryx and Leptoreodon we
shall find the forms which later diverged into the lines terminated by Lep/o-
meryx and Protoceras. Further, this group is unmistakably related to the
main tylopodan stem. Camelomeryx and Leptoreodon are already, it is true,
quite distinctly separated from Protylopus, but the difference lies almost entirely
in the anterior region of the skull and in the character of the incisors and
canines. The remainder of the skull and dentition are of the same type of
structure, as are also the limbs and feet, only in Protylopus the elongation of tne
manus and pes and the reduction of the lateral digits have been carried one
stage farther. This near alliance greatly strengthens the conclusion already
reached that the White River selenodonts, such as Protoceras, Leptomeryx, and
Fly pertragulus, are derivatives of the tylopodan stem. The latter is in some
sense intermediate between Leftomeryx and the main tylopodan line, for in it
the canines have retained or reacquired their original form and function.
HHypertragulus, therefore, cannot have been derived from Camelomeryx or
Leptoreodon, but its very close resemblance in nearly all other respects to
Leptomeryx shows that its Uinta predecessor must have been very much like
those genera, except in the character of the incisors and canines. In the
White River it runs a course closely parallel to that of Leptomeryx, though
keeping an even more markedly tylopodan physiognomy, which makes it look

like a miniature Poebyotherium, save for the long and slender canines.

(?) Oromeryx Marsh.

Oromeryx Marsh, Amer. Journ. Sci., 3d Ser., xiv., p. 364 (somen nudum).
Oromeryx Marsh, Ibid., xlviii., p. 269.

This genus may be distinguished from the preceding ones, Leptotragulus,.
Leptoreodon, and Camelomeryx, by the absence of diastemata in the dentition,
and from Protylopus by the much less advanced reduction of the lateral digits
in both manus and pes, and by the shape of the upper molars, in which the
anterior half of the crown decidedly exceeds the posterior half in breadth,
giving a curiously asymmetrical shape, which is most marked in m®; the
external median buttress is much more prominent than in Pvotylopus.. P23 is
inserted by two fangs only. In the absence of information concerning the
canine teeth it is uncertain whether Ovomeryx should be referred to the
present family or the preceding one, and for the same reason we cannot

definitely point out the White River successor of the genus. In a general

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84
way it is clear that it is allied to the other Uinta selenodonts described in the
foregoing pages, and it is not at all impossible that Oromeryx may prove, when
better known, to be the forerunner of Hyfertragulus. Both genera are charac-
terized by simplicity of the premolar teeth, and both have very similar molars,
which in Ovomeryx and less markedly in Aypertragulus are distinguished by
the narrowness of the posterior half of the crown and the consequent asym-
metry of form. In the character of the skull, limbs, and feet nothing is known
to forbid or render improbable the derivation here suggested. At the same
time it must be remembered that this is only a suggestion, and quite as good
reasons may be given for deriving A/ypertragulus from Leptotragulus. The
difficulty in deciding the question comes from our ignorance regarding much
of the structure of the two genera from the Uinta, and until these are better
known we shall not be able to determine with accuracy even the family or
families to which they should be referred, still less to indicate their successors
in the White River fauna.

Famity II]. HOMACODONTID-.

Bunomeryx Wortman.
Bull. Amer. Mus. Nat. Hist. N. Y., x., p. 97.

This exceedingly interesting form is not represented in the Princeton
collection, and I therefore have nothing to add to Wortman’s account. One
of the most significant facts regarding Aunomeryx is the structure of its upper
molars, which strongly suggests, as Wortman has pointed out, that the postero-
internal crescent of the selenodont upper molar is not the hypocone, as has
hitherto been taken for granted, but the metaconule. This determination is of
the greatest interest as showing that the elements which make up the molar
crown may develop in different ways, and that cusps occupying similar positions
are not always homologous. The same fact has already been established with
regard to the premolars. It is confirmatory of Wortman’s view that the Uinta
selenodonts almost all have more or less asymmetrical upper molars, due to
the fact that the anterior half of the crown is broader transversely than the
posterior half. In Ovomerya, and especially in m2 of that genus, this asym-
metry is most clearly shown, but it has almost entirely disappeared in the
White River genera. On Wortman’s hypothesis the asymmetry seen in the
teeth of the earlier selenodonts is intelligible enough; it is simply due to the

fact that the metaconule has not yet grown to the full size of the protocone.

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The taxonomic position of Bunxomeryx is from one point of view suf-
ficiently clear. As Wortman points out, it is obviously the direct descendant
of the Bridger Homacodon, and should be referred to the same family as the
latter. What this family should be called is another question, and one that
cannot easily be answered. The European Dichodune has upper molars of a
very similar type, and, so far as it is known, the rest of the structure seems to
agree very well with that of the American genera, which may perhaps belong
to the same family. It seems more probable, however, that the two groups
are distinct, the Homacodontide standing in the same relation to the Tylopoda
as the Dichobunide are believed by Schlosser to occupy with reference to the

Pecora.
Famity IV. OREODONTID~.

Protoreodon Scott and Osborn.

PuaTeE III., Fics. 19-23; PLATE IV., Fics. 24, 25.
Agriocherus Marsh (zon Leidy), Amer. Journ. Sci., 3d Ser., ix., p. 250.
Eomeryx Marsh, Ibid., xiv., p. 364 (women nudune).
Protoreodon S. and O., Proc. Amer. Phil. Soc., 1887, p. 257.
ELomeryx Marsh, Amer. Journ. Sci., 3d Ser., xlviii., p. 266.
? Agriotherium Scott (zon Wagner), Proc. Amer. Phil. Soc., xxxvil., p. 79.

The essential features of the structure of this genus were quite fully de-
scribed in a previous paper (’89, pp. 487, ff), yet the recently made collections
add materially to our knowledge of it, and for the sake of completeness an
account of the skeleton will be given here, though that involves a number of
repetitions. Specimens of FProtoreodon are about the most abundant of Uinta
fossils, though well-preserved ones are far from common. Even the best of
them have in nearly all cases suffered more or less from crushing, and it is
surprising to see how much the appearance of a fossil is changed according to
the direction in which the crushing has taken place. Especially is this true of
the skull.

The oreodont family had already become distinctly established as such in
Uinta times, and is very clearly distinguished from the other contemporary
selenodonts. The genera of the succeeding White River stage differ com-
paratively little from those of the Uinta, of which VProtoreodon is the most
abundant, as well as the most important.

The dentition is peculiar and of considerable morphological interest ; the
3

teeth form a closed series without diastemata, and the formula is 13, C+, P4, M3.

3

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86

A. Upper Jaw. (Plate IIL, figs. 20-23; Plate IV., fig. 25.) The incisors
are rather small, antero-posteriorly compressed, and chisel-shaped. These
teeth would seem to vary in number; in some specimens, at least of P. parvus,
three are present, while in P. (Agriotherium) paradoxicus only one or two are
found. Wortman says on this subject: ‘In all of our material I have not yet
seen a specimen among the oreodonts other than Lepforeodon that has a full
set of incisors in the upper jaw. Marsh figures the type of Aomeryx pumilus
with but two superior incisors, and if Protoreodon has the full complement, as
believed by Scott, then the two genera are certainly distinct. In two speci-
mens in the Museum collection which correspond closely with Protoreodon
parvus, as described by Scott, there is but a single incisor on each side above,
and the premaxillz are widely separated from each other in the median line.”
(98, p. 96, foot-note.) Ordinarily such a difference in the number of the
incisors and in the form of the premaxillaries would certainly be sufficient
ground for a generic distinction, but in the present instance, as in the titano-
theres, the variability is so great that for the present at least it seems better to
include them all under one term, with the exception of AYyomeryx, which
seems to be distinct. The canine is of the characteristic oreodont form, with
D-shaped transverse section and abraded upon the posterior face. It is, how-
ever, relatively a little more slender, elongate, and recurved than in the later
representatives of the family.

A very short diastema succeeds the canine, but only sufficient to provide
for the caniniform p;, which of course bites behind the upper canine. The
premolars are of thoroughly oreodont type, but are somewhat simpler, more
compressed, and more trenchant than those of the White River genus, though
in the structure of these teeth there is considerable specific and individual varia-
tion. The first and second premolars are each carried upon two fangs and
have simple, compressed, and trenchant crowns, which, when seen from the
outer side, have the cordate profile characteristic of the family; p? differs from
pt in the presence of a better developed internal cingulum. P# is always im-
planted by three roots and is wider transversely than p2, but the development
of the inner side of the crown varies greatly. In P. paradoxicus (Plate IV.,
fig. 25) there is only a feebly marked internal cingulum; in P. mznor (Plate
IIL., fig. 23) the cingulum is quite distinct and a small deuterocone makes its
appearance, while P. pavvus (Plate III., fig. 20) and P. pumzlus display an in-
creasing size of this element. In the latter species Marsh figures the deutero-

cone as being almost as large and as completely crescentic as on p+. (94, p.

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266, fig. 18.) P+ is composed, as usual, of two transversely placed crescents,
of which the outer one is more concave externally than in the other pre-
molars; in P. paradoxicus the inner crescent is more conical and has less
clearly marked horns than in the other species.

The upper premolars of Oveodon are just such as might be expected in
the direct successor of the Uinta genus. Leidy says of the anterior three:
“ Their crown is a trilateral pyramid, with a pointed apex and a broad external
cordiform surface. The narrower internal surfaces appear as triangular in-
clined planes, separated by a median acute ridge extending from the point to
the base of the crown. The anterior of the internal surfaces forms at the
base a pair of shallow pouches, defined by a double festoon. The posterior of
the same surfaces forms a single and larger pouch at the base of the crown,
included by a single and thicker festoon. This latter in the third premolar
almost assumes the dignity of an additional lobe to the crown, resembling the
internal lobes of the true molars.” (’69, p. 81.)

The upper molars of Protoreodon are primitive in a very interesting way,—
viz., in the retention of the anterior intermediate cusp (protoconule), though
in other respects these teeth are already well advanced in the assumption of
the selenodont character. They are extremely brachyodont, and are broad in
proportion to their antero-posterior length. In size they increase from the
first to the third. The external crescents are more concave on their outer
faces than in Oveodon, and the median ribs upon those faces are far more
prominent, as are also the external buttresses, all of which constitutes a marked
resemblance to the molars of Protylopus and the Leptomerycide. The inner
crescents, especially the anterior one, have less extended horns than in Oreo-
don, and the median valley is thus more widely open. The unpaired cusp is
very small and in worn teeth soon becomes unrecognizable; such molars con-
siderably resemble those of Leptoreodon and Camelomeryx in a corresponding
stage of wear. The cingulum is much better developed than in Oreodon, and
is almost continuous upon the front, internal, and hinder faces of the teeth.

The molars of Oveodon are so very familiar that they require no descrip-
tion. Suffice it to say that a comparison with those of the Uinta genus is
extremely suggestive of a direct genetic connection between the two.

B. Lower Jaw. The incisors have simple, chisel-like crowns, and the
canine has become one of them in form and function; these teeth are much
more erect than in Protylopus or the Leptomerycide. The premolars are dis-
tinctively of the oreodont type, but they are simpler and much more com-

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pressed and trenchant than in the White River genus. The first premolar is
caniniform and is more slender and pointed than in Oreodon, it is succeeded
by pz after an interval which, though very short, is distinctly longer than in
the latter genus. Pz is a small, simple, and much compressed cone; pz is
larger, especially in the fore-and-aft dimension, and is obtusely pointed; from
the apex a quite prominent ridge runs down the inner side of the crown,
partially enclosing a posterior fossette. In pz this inner ridge has become a
well-marked cusp, much like that in Leptoreodon.

Leidy’s admirable description of the lower premolars of Oreodon will
show the changes which characterize that genus: “ Their crown is a broad,
trapezoidal pyramid, widest behind, and with an acute crescentoid border
rising in a median point. From the latter an oblique ridge descends in-
ternally, and in the third [fourth] premolar terminates in a large, trilateral,
pointed tubercle, which springs from the middle of the base of the crown and
rises nearly as high as the principal point. In the premolars in advance the
tubercle just mentioned is nearly obsolete, and the oblique ridge appears to
expand into the base of the crown. Back of the oblique ridge the crown
presents a fossa more or less closed internally by a tubercle or ridge... ..
In advance of the oblique ridge mentioned, the inner part of the crown forms
a broad, sloping concavity, usually enclosed at bottom by a narrow, festooned
basal ridge.” (69, p. 82.)

The molars are much more primitive than those of the upper jaw and
have many points of resemblance to the lower molars of Agriochwrus. The
internal cusps are conical rather than crescentic, and the outer ones, while cres-
centic, are quite thick; the valleys are very broad and shallow; the anterior
pair of crescents is separated from the posterior pair by a deep depression ;
small basal tubercles are developed on the inner cusps. Mg has a very large,
basin-like heel. In Oveodon the lower molars have become typically seleno-
dont, almost as much so as in the deer, while Agviochwrus retains a structure
very closely like that of Protoreodon,—a significant fact.

The milk dentition is only imperfectly known, but one specimen which
retains m1 and dp4 displays some points of interest. The deciduous pre-
molar is completely molariform, but has more the molar pattern of Agrio-
cherus than have the true molars of Protoreodon. This approximation to
Agriocherus is manifest (1) in the greater concavity of the external crescents ;
(2) in the more massive and rounded shape of the antero-external buttress ;

(3) in the greater breadth of the external median buttress, which is not com-

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pressed as in the true molars, but is invaded by the valley, just as in Agvzo-

cherus, though the buttress is much less prominent than in the latter.

MEASUREMENTS.
P.
‘Ge pes Gatien tice
Upper dentition, length F : 0.070 0.067
“* canine, ant.-post. diam... .006 .0055
oe «« transv. diam. : .006 .005
‘* premolar-molar series - : 1052 .050 0465
‘« premolar series, length —. .030 -02 .025
«« molar series, length . : .026 .022 .023 .O21
UG PEA length : ; é .006 .006 .006
P-2, length : : 3 .007 .0065 .006
«« P-2, width 5 : : .003 .004
ce P=3;-length E : , .007 .007 .006 .0065
cc P-3, width 5 ; . .0065 .0065 .005 +0055
«« P-4, length : s ; .006 _ .006 .006 .006
P-4, width 5 : o .009 .009 .009 .008
M-1, length. ; : -008 .0065 -008
«« M-1, width . é : .0095 .009 .009
M-2, length . : A .009 -0085 .0085 .0085
«« M-2, width : : ¢ -O1L O11 OIL -O105
«« M-3, length : : : .O10 .009 -009 .009
‘«« M-3, width é ; é .O12 O12 “012 -O115
Lower premolar-molar series : -056
‘« premolar series, length . .028
‘* molar series, length . : .028 .028
‘« P-1, length : : , .006
‘« P-1, width : 5 : .005
«« P-2, length 0 ; . -006
«« P-3, length Q ; : .008 .0075
«« P-3, width : E : .0035 .003
«« P-4, length 2 : : .008 .008
«c P-4, width a : 5 .005 .0O04
CC Vinten ge these ; : .0075 .008
«« —M-1, width 3 : ; .006 .0055
«« M-2, length j : : .0075 .008
«« M-2, width ; p ; .007 .006
‘«« M-3, length 6 6 : .O12 .O12

‘« M-3, width 3 ; c .007 .0065

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gO

The skull (Plate III., fig. 19; Plate IV., fig, 24) is represented by several
fine specimens in the two collections, which give a much more accurate idea
of its structure and proportions than did the single very imperfect individual
upon which my previous description was founded. (’89, pp. 488-490.) It is
now obvious that the whole appearance and character of the skull are typically
oreodont, though certain resemblances to the agriochcerids may be made out,
and in several respects the skull, as would naturally be expected, is decidedly
more primitive than in the White River representatives of either family. The
cranium is long and narrow and low, especially in P. paradoxicus, and the face
is short; the position of the orbit is somewhat variable, its anterior border
being over the front part of m2 or the hinder part of m+. The occiput is
low and narrow, and is drawn out dorsally into the wing-like processes so
characteristic of the family; the zygomatic arch is slender, elongate, and
nearly straight, and the orbit is widely open behind. No lachrymal pit has
been detected. The muzzle is short, but narrow and tapering and abruptly
truncate in front. The mandible is characteristically oreodont in form.

In details the skull structure is completely oreodont, though in several
respects it is more primitive than that found in the genera of the White River
and succeeding stages. The basioccipital resembles that of Oveodon, but is
somewhat narrower, as are also the exoccipitals, but the foramen magnum is
relatively much larger and the condyles more widely separated. The par-
occipital processes are slender and appear to be relatively less elongate than in
the White River forms; they have a rather more anterior position than in the
latter. The limits of the supraoccipital are not clearly shown in any of the
specimens, though doubtless it extends over upon the dorsal side of the
cranium as it does in Oreodon, and, as in that cenus, it forms a pair of promi-
nent wing-like processes which extend backward, overhanging the occiput;
they are best developed in P. paradoxicus, in which they are quite as conspicu-
ous as in O. caudbertsont. The occipital crest is not very prominently developed
and does not pass so directly into the root of the zygomatic process as it does
in the later genera of the family. In none of the individuals that I have ex-
amined is the tympanic well preserved; it is almost certain, however, that the
bulla was very small and that it was provided with a tubular meatus, much as
in O. culbertsont,

As in the White River genus, the parietals are very long, roofing in
nearly the whole of the cerebral fossa, and they are somewhat broader pro-

portionately than in the former. For their entire length they support a thin

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I
UINTA SELENODONTS 9

but high and conspicuous sagittal crest, which is not so straight as in Oreodon,
but is arched from before backward, much as it is in Agriocherus. The squa-
mosal is very large and forms much the greater part of the cranial wall, though,
corresponding to the broader parietal, it is somewhat narrower than in Oreodon.
The glenoid cavity and process are typically oreodont, though the process is
somewhat smaller and less massive than in the White River genus. The zygo-
matic process, which is shorter than in O. cadbertsonz, curves out boldly from
the side of the skull, but is slender and pursues an almost horizontal course,
not arching upward and then downward nearly so much as in the White River
forms. The jugal, on the contrary, is longer than in the latter and extends
much nearer to the glenoid cavity; it is very slender and is not notched to
receive the zygomatic process as it is in Oreodon, and the postorbital process
is so feebly developed that the orbit is even more widely open behind than in
Agriocherus. Asa whole, the zygomatic arch is more elongate, more slender,
and much more nearly horizontal than in Oreodon, in which the arch descends
quite strongly anteriorly, a feature which is due to the increased height of the
ascending ramus of the mandible.

All of the skulls which I have examined are more. or less damaged in
front of the orbit, rendering it impossible to make out the limits of the lach-
rymal, though it may be seen, at least in some specimens, that the lachrymal
pit, which is so characteristic of the later members of the family, is not present.
A difference from Ovyeodon may be observed in the frontals, which descend
forward at the forehead and are flat, not swollen and arched by the large
sinuses. The forehead is broad and lozenge-shaped, narrowing abruptly be-
hind and gradually in front, and displaying obscurely marked temporal ridges.
The postorbital processes are in P. parvus quite long and decurved, much

shorter in P. paradoxicus. The nasals are long

g, narrow, and quite convex

transversely ; in front they terminate in points and project well beyond the
premaxille. The anterior nares are small, terminal, and almost vertical in
position.

The premaxillaries are small, and, as in Oveodon, but little of them is
visible in side view; the alveolar portion is low and weak, and in such species
as P. paradoxicus, which have reduced incisors, the two bones do not meet
in the median line. The incisive foramina are quite large and the spines are
long, extending back to p1. I can discover no indication of the curious
dorsal expansion of the ascending ramus which in Oreodon is received into a

notch in the maxilla. The maxillary is shaped much as in O. cudbertsoni, but

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is somewhat lower vertically; its palatine processes are narrow and short,
and quite concave transversely. The palatal notches are very shallow, and,
as the jugal joins the maxillary farther back than in Oreodon, the alveolus of
m+ is not so bar-like as in that genus. The palatines are quite large and make
up an extensive part of the bony palate, reaching forward to p+. As in Oreodon,
the palate is of nearly uniform width throughout. The posterior nares are inter-
mediate in character between those of Orveodon and those of Agriocherus ; they
are wider than in the latter, but extend farther forward than in the former (to
m2), and thus the fore-and-aft extent of the canal is considerably greater.

The mandible is as characteristically oreodont as the rest of the skull; the
horizontal ramus is of moderate length, but deep and compressed, tapering
forward to the abruptly inclined chin. The symphysis is short and very steep,
and in old individuals the two rami are sometimes codssified at this point.
The shape of the symphyseal region is one of the most marked differences
between Pyotoreodon and the other Uinta selenodonts, such as Protylopus and
Leptoreodon. The ascending ramus of the mandible is shaped very much as
in Orcodon but is lower, the condyle being raised much less above the level of
the teeth. The angle is very broad and extends well behind the condyle,
decidedly more than in Ovcodon, but less than in Leptoreodon ; its border is
thickened, as in the former. The coronoid process is higher and more re-
curved than in the White River genus, and the masseteric fossa extends

farther down upon the jaw.

MEASUREMENTS.

P. parvus. P. paradox.

Skull, basal length 5 . : : - : 0.127 0.132
Cranium, length to anterior margin of orbit . A .073 -081
Face, length, orbit to premaxilla . : : ; O61 .O51
Sagittal crest, length . : A 3 j . .052 .060
Zygomatic arch, length : : : : : -059 .056
Skull, breadth across zygomata_. : : ; .086 .078
Mandible, length . ; : : ; : : fede 2.109
depth at mz : 5 : F : .O21 .026
Py ; : ; : : .o18
breadth of angle . : : ; : -O45
height of condyle : . . . .047

The brain is relatively smaller than in Oveodox and much more simply

convoluted. The hemispheres are particularly small, leaving the cerebellum

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UINTA SELENODONTS

entirely uncovered and, apparently, even a portion of the corpora quadrigemina.
The cerebrum is pear-shaped and narrows anteriorly, abruptly so in front of
the temporo-sphenoidal lobes; the latter are proportionately quite large. The
convolutions are very simple and take a longitudinal course. On the dorsal
surface of the hemisphere only two sulci are visible, one of which is the lateral
and the other may be the suprasylvian, though they come together in front,
enclosing a pyriform gyrus between them. The shape of the hemispheres is
quite as much like those of Leptomeryx as it is like those of Oreodon. The
posterior region of the brain, including the cerebellum and medulla, is very
long proportionately.

The vertebral column is represented only by scattered vertebre from all
the regions in a more or less favorable state of preservation and belonging to
numerous individuals. Only in minor details do they differ from those of
Oreodon.

The atlas is very similar to that of the White River genus; it is short
antero-posteriorly, but broad and with widely extended transverse processes.
The odontoid process of the axis is narrower and more peg-like than in Oreo-
don, and the other cervical vertebre are rather longer in proportion and some-
what more opisthoccelous ; they all, except the seventh, appear to be perforated
by the vertebrarterial canal. The trunk vertebre do not offer any noteworthy
distinctions from those of Oveodon except that they are somewhat lighter and
more slender. The tail was evidently very long and stout.

The fore-limb, so far as we have it, differs very little from that of Oreodon.
The humerus is almost exactly as in that genus, but is more slender and has
a much less conspicuous deltoid ridge. The ulna has a stouter shaft and the
radius a more slender one, but the peculiar articulations of the elbow-joint are
just the same in the two genera.

The manus (Plate III, fig. 21) is somewhat less modified than in the
White River types, yet the difference is not great. In all the later oreodonts
the lunar rests entirely upon the unciform and has only a lateral contact with
the magnum, which has shifted beneath the scaphoid. In Protoreodon this
change is in an incipient stage, and the lunar still rests partially upon the
magnum, which is not entirely covered by the scaphoid. The trapezium is
better developed and the pollex is a little larger relatively than in Oreodon.

Pelvis, femur, tibia, and fibula differ so little from those of Oreodon that
they require no particular description, and the pes is likewise in almost the

same stage of advancement, though with some significant and interesting differ-

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94 UINTA SELENODONTS

ences. The astragalus is somewhat narrower and has a rather more asym-
metrical proximal trochlea; in the distal trochlea the cuboidal facet is even
narrower than in the White River types. The calcaneum has a much more
slender tuber, and the sustentaculum is more prominent, though very incon-
spicuous, which is a characteristic of the entire family. The cuboid is higher,
narrower, and more deeply incised by the calcaneal facet, while the astragalar
surface rises higher proximally. The navicular also has a greater proximo-
distal diameter. The meso- and ecto-cuneiforms are codssified, though their
limits are still clearly visible, and, as in the White River types, the former is a
little shorter than the latter. The whole tarsus is conspicuously higher and
narrower than in the subsequent genera of the family, in which the tendency
was continually to become short and broad, a tendency which reached its
maximum in MJerycocherus ; Protoreodon departs much less in this respect
from the tylopodan stem as represented by Leptoreodon and Camelomeryx.

The metatarsus is also elongate, as much so proportionately as in Lep-
toreodon. According to Marsh (’94, p. 267) at least a rudiment of the hallux
is retained, as I have also shown to be true of Ancodus. ('95a, p. 486.) The
other metatarsals closely resemble those of Oreodon except for their relatively
greater length, the median pair are enlarged, and the lateral pair (ii. and v.),
though longer, are almost as slender as in the White River genus.

The phalanges are much as in the latter, but longer and more slender ;
those of the second row have the distal trochlea only slightly asymmetrical,
showing a less degree of convergence of the hoofs than in any recent artiodac-
tyls except the Tylopoda. The unguals are longer, narrower, more pointed,

and altogether more claw-like than in the later members of the group.

MEASUREMENTS.
P. parvus. P. parad. P. sp.
Astragalus, length. : . : . 0.0225 0.026
breadth of proximal trochlea_ . .OIl -O13
Calcaneum, length . c c : : .039 .048
dorso-plantar diameter of tuber, O10 -O13
Cuboid, height , : ; . : .O13
width : : : é 5 -O10
Metatarsal ii., length : : 5 : -049
Nig, <s : ; 5 : .060
Venn 5 ; : : 061

Wan oe : : : ; .O51

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The species of Protoreodon are as follows:

Protoreodon parvus S. and O.
Proc. Amer. Phil. Soc., 1887,.p. 257.
Characterized by the-presence of three upper incisors and by the small
development of the inner cusp on p®. Size moderate. Upper molars with

strongly concave outer crescents.

Protoreodon pumilus Marsh.
Agriocherus pumilus Marsh, Amer. Journ. Sci., 3d Ser., ix., p. 250.
Eomeryx pumilus Marsh, Ibid., xlviii., p. 266.
Upper incisiors two; p® like p*; upper molars with less concave outer

crescents.
Protoreodon paradoxicus Scott.

Agriotherium paradoxicum Scott, Proc. Amer. Phil. Soc., 1898, p. 79.

Cranium very long, face short; upper incisors one, premaxillaze not meet-
ing in the median line. Upper molars with very concave outer crescents; p?
without inner cusp.

Protoreodon minor sp. nov.

Size smaller than preceding species; p* with very small inner cusp.

In addition to these a large species, almost rivalling Oreodon culbertsoni in
size, is indicated by limb and foot bones in the Princeton collection and in that
of the American Museum. (See Plate III, fig. 22.

The Taxonomic Position of Protoreodon and the Relationships
of the Oreodontde.

There would appear to be two lines of development included within
the genus Protoreodon, one of which is characterized by the reduction of the
upper incisors, and which culminates in the genus yomeryx, which is without
upper incisors altogether. In the other line the incisors are retained. The
first series apparently died out at the end of the Uinta, leaving no successors
in the White River. The second series, represented especially by P. parvus,
seems without doubt to be the direct forerunner of Oreodon and its successors.
The Uinta genus resembles the White River form in every part of the dentition,
skull, and skeleton, but is, of course, less modified and in every way what we

should expect the ancestral genus to be. Thus the incisors and canines have

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96
already assumed their characteristic shape, the lower canine going over to the
incisors and the first lower premolar becoming caniniform. The upper molars
retain the fifth cusp (protoconule) in the anterior half of the crown, but their
form is already characteristically oreodont; the lower molars are less advanced
and resemble those of Agriochwrus in the conical inner cusps and the widely
open valleys. The premolars are typically oreodont but somewhat simpler in
construction than those of the White River representatives of the family.

The skull is oreodont but has a longer and less capacious cranium than in
the later genera of the group, with orbits widely open behind and no lachry-
mal pit; the mandible is likewise oreodont in shape, but has a longer and more
recurved coronoid process and angle more extended behind the condyle. The
vertebral column differs but slightly from that of the White River genus, the
principal difference being in the more peg-shaped character of the odontoid
process of the axis and in the longer and more massive tail. The entire
character of the limbs is oreodont; scapula, humerus, ulna and radius, pelvis,
femur, tibia, and fibula differ in no important way from those of Oreodov itself,
only the manus and pes are distinctly more primitive than in the latter. In
the manus the displacement of the lunar over upon the unciform is already
indicated, but is much less extreme than it afterwards became, and the pollex
is somewhat less reduced. In the pes a remnant of the first metatarsal is still
(fide Marsh) attached to the ento-cuneiform. The phalanges are rather more
slender and the unguals more pointed than in Oreodon.

While there is little room left for doubt that Protoreodon is thus the
ancestral form whence were derived Oveodon and its successors, Eporeodon,
Mesoreodon, Merycocherus, Merychyus, the Uinta material gives us no help in
determining the genealogy of those curious aquatic oreodonts, Leptauchenta
and its successors. This genus suddenly makes its appearance in the upper
White River (Protoceras beds), and nothing has yet been found in the Oreo-
don or Titanotherium beds which can be regarded as ancestral to it, or which
will explain its exact relationship to the more typical members of the family.
Whether this line had already begun its separate existence in Uinta times, or
whether it first branched off from the main stem in the older White River,
must be left for future discovery to determine.

A larger and more important question is that concerning the relationship
of the oreodonts as a whole to the other artiodactyl groups. Upon this sub-
ject the most diverse possible opinions have been expressed by the various

students of the problem. Leidy was the first to call attention to the manifold

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tylopodan features in the structure of the oreodonts, and spoke of the family as
uniting characteristics of the deer, camel, and hog. ('69, p. 71.) This phrase,
however, should probably be regarded as descriptive rather than as expressing
an opinion upon the taxonomic question, concerning which Leidy seems to
have held no decided views. Cope brought the family into relation with the
tragulines (’88, p. 1084), but here again, as in so many of Cope’s phylogenetic
schemes, the connection seems to have been regarded as formal and technical
rather than actual. Marsh (’77, p. 365) has vaguely expressed an opinion
according to which the nearer allies of the oreodonts are to be sought for
among the anthracotheres (Hyopotamus or Ancodus) of the Old World. Sub-
stantially the same opinion is elaborated in my monograph of the family.
(‘g1a@, p. 391.) Riitimeyer ('83, p. 98) in a very brief and cursory way ex-
pressed his belief that the oreodonts are nearly related to the camels, and
speaks of the “in Nordamerika so stark vertretenen Vorlaufern der Camelina
(Oreodon, Procamelus, Leptauchenia, etc.).” Schlosser has adopted the same
view; he says of the family: ‘‘ Sie nehmen tiberhaupt eine ganz eigenthimliche
Mittelstellung zwischen den Suiden und den Traguliden ein” (’87, p. 46),
“Von den altesten Oreodontiden haben sich wohl die Tylopoden abgezweigt”
(p. 48). From the same ancestral stock Schlosser derives the anoplotheres,
anthracotheres, hippopotamuses, and suillines. (’87, Table, p. 42.)

The testimony of the Uinta selenodonts, while not entirely conclusive, is
distinctly in favor of the opinion held by Riitimeyer and Schlosser,—namely,
that the oreodonts are related to the Tylopoda, or rather that that term should
be employed in a broad sense, of subordinal value, and so extended as to in-
clude the oreodonts, and that the latter are an offshoot of the same stock
which gave rise to the modern camels and llamas. The recovery of the
Uinta fauna has for the first time made clear what a dominant position the
Tylopoda long held among North American artiodactyls, and how widely
ramified and diversified they became. We cannot yet, it is true, definitely
trace back the oreodonts to ancestors common to them and to the main line
of tylopodan descent, and until that is done the association of both groups in
one suborder must remain open to some question. On the other hand, it is
a highly important and significant fact that in the Uinta the gaps between the
various families of characteristically American selenodonts were not nearly so
wide as they afterwards became through the divergent courses of develop-
ment followed by these families, and that they were then obviously converg-
ing back to a common term. Even in Uinta times, however, the oreodonts

7

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98
were the most isolated and therefore the most clearly defined of all the seleno-
dont families, but such genera as Leptorcodon and Camelomeryx, in which the
lower canine has become a functional incisor and the first lower premolar is
caniniform (one of the most strikingly characteristic features of the oreodonts),
tend greatly to diminish the gap between the oreodonts and the undoubted
tylopodans. Even so highly differentiated a type as the White River Proto-
ceras is in many respects continues to preserve certain resemblances to the
oreodonts. Leptomeryx also retains recognizable traces of the same relation-
ship, and there is a great deal to be said in favor of the opinion that it was
derived from an ancestor in which pz was caniniform.

If, as Wortman suggests, Bunomeryx represents the transitional stage of
dental development for both cameloids and oreodonts, the principal difficulty
in the way of connecting the two groups will disappear. This difficulty lies in
the uncertainty whether the tetraselenodont upper molar of Protylopus and its
allies was derived from a tooth which retained the anterior intermediate cusp,
as is certainly true of the oreodonts. As aiready pointed out, the asymmetry
of the upper molars in nearly all of the Uinta selenodonts favors the conclu-
sion that they were derived from a type like that of Bunomeryx.

Another difficulty in the way of referring the oreodonts to the Tylopoda
lies in the character of the cervical vertebra, which in all the genera of the
family are short, and show no tendency to assume any of the peculiarities
which are so marked in the family Camme/id@, and which are usually regarded
as diagnostic of the suborder Tylopoda. These peculiarities are already well
defined in the White River genus Pocbrotherium (though in several respects
they are less decided than in the later genera of the line), and it may reason-
ably be supposed that in Protylopus also they were present, at least in their
incipient stages. However that may be, these features of the cervical vertebra
seem to be confined to the main line of tylopodan descent, the line which in
this paper has been designated as the family Camelide@, for in all of the other
White River selenodonts (Orcodon, Leptomeryx, Protoceras, etc.) the neck is
either short or of only moderate length, and its vertebree are of the ordinary
artiodactyl type of construction. It is most unfortunate that the structure of
the neck is still unknown in all of the Uinta genera except Protoreodon, and
hence we are unable to trace the rise and development of the peculiar cameline
cervical vertebrae and to determine how early these peculiarities first made
their appearance.

From the Uinta onward the history of the oreodont family is long and

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for the most part clearly recorded, extending, as it does, through the Loup
Fork at the top of the Miocene. During this long period they were nearly
or quite the most abundant of North American mammals, but they were very
conservative and underwent relatively little change, and so far as is known
they never migrated to any other continent. Throughout this time they re-
tained their characteristic form of skull and dentition, together with the same
short neck, long body and tail, short limbs and feet, which we find in the Uinta
Protoreodon. In their general appearance and proportions there is little to
suggest relationship with the Tylopoda, but much to suggest a connection with
the suillines, though any such connection must be exceedingly remote.

While the line of descent from /rotorcodon is thus reasonably clear, it is
not yet possible to determine the ancestors of that genus. In some respects
the molars of the smaller species of the Bridger He/ohyus suggest the deriva-
tion of the Uinta genus from it, but, on the whole, Homacodon, or some nearly
allied form, seems to be the more probable ancestor, which is as much as to
say that the oreodonts appear to lead back to the same group of Bridger
artiodactyls as do the other Uinta selenodonts. If this conclusion is sustained
by future discovery, it will completely justify Schlosser’s opinion, already
quoted, and will show that the oreodonts represent a peculiar side-branch of
the tylopodan stem, standing in somwhat the same relation to the Camehde
proper as the tragulines do to the Pecora. It will also serve to explain the
many resemblances which are to be noted between the oreodonts on the one
hand and such genera as Leptomeryx and Protoceras on the other, resemblances
which are exceedingly puzzling on any other hypothesis.

These conclusions are of great interest, and if sustained they will help to
clear up many obscure problems of phylogeny, but it must not be forgotten
that they are still only tentative; new discoveries among the artiodactyls of
the Washakie and Bridger proper may at any time overthrow them. I think,
however, that they are justified by the evidence now at hand.

Hyomeryx Marsh.
Amer. Journ, Sci., 3d Ser., xlviii., p. 268.

I have not seen any specimens of this genus, which is described as having
lost all the upper incisors. Marsh’s figure also shows that the upper molars
are different from those of Protoreodon in having much less concave external
crescents and less prominent outer buttresses.

No White River genus is known that can be regarded as a descendant of

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TOO

FIyomeryx, which appears to be merely an abortive side-branch of the oreodont
stem that led to nothing. At the same time this genus and the species of
Protoreodon with reduced upper incisors would seem to have been the domi-
nant representatives of the oreodonts in the typical Uinta horizon (horizon C).
All the specimens of P. farvus which I have seen were found in the clays of
horizon B, and while the Uinta collections are not yet sufficiently complete to
give certainty upon such points, it seems exceedingly probable that in the Uinta
proper the main line of oreodont development was overshadowed by the tem-
porary abundance and importance of this short-lived group. This reasoning
proceeds upon the assumption that structures once lost are not regained, and
such certainly appears to be the normal course of evolution in the mammalian
phyla. At the same time it must be remembered that it is an assumption, that
possibly the incisors may have been partly suppressed and again redeveloped.
The series Protylopus, Poebrotherium, Gomphotherium, etc., shows us that teeth
may be greatly reduced in size and subsequently enlarge, and we cannot say
with entire confidence that the process of rehabilitation may not go farther,
and that teeth which are lost in the adult may not become functional again in
a descendant. It is most important that we should not dogmatize concerning
evolutionary processes on @ priori grounds, and that we should await the

evidence before coming to a decision upon these problems.

Famity V. AGRIOCHCERID.
Protagriochcerus gen. nov.
PLATE IV., FIGURES 26-28.

This genus, which is represented by a species of considerably larger
stature than those of any other genus of Uinta selenodonts, is founded upon a
specimen belonging to the American Museum of Natural History (No. 1818).
It is much to be regretted that all the known material is so very imperfectly
preserved that many interesting phylogenetic questions cannot yet be settled.
The dentition (Plate IV., figs. 26, 27) is of a character intermediate between
the oreodonts and agriocheerids.

The dental formula is: I+, C+, P4, M3. The incisors appear to have
already undergone some reduction, and in the type specimen only the fang of
i= is visible; this fang is stout, of circular section, and is implanted quite near
to and in advance of the canine. If the other two incisors were present they

were probably small, as the premaxillary is so narrowed as hardly to allow

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IOI

space for three full-sized teeth; however, the point is not an easy one to
decide. The canine is of the typical oreodont (or agriochcerid) pattern, as is
plainly apparent, although both canines are broken away nearly level with the
alveolus. From the broken surface several facts may be learned: the section
is D-shaped, with the posterior surface nearly plane or even slightly concave,
while the fang is curved, much as in Agriochwrus. From the characteristic
form of this upper canine we may confidently infer that, as in Protoreodon, the
lower canine had already gone over to the incisors and that p>; had assumed
its shape and function.

The first premolar also is represented only by the roots, the crown being
broken on each side. This tooth follows the canine after an interval which is
relatively no greater than in Protoreodon, and this lack of a diastema con-
stitutes a very marked difference from Agriocherus. Another difference from
the latter is in the proportionately larger size of p+, for though it was evidently
the smallest of the series, it was not so much reduced as in the White River
genus. The second premolar is larger in every dimension than p+, especially
in the antero-posterior one; the crown is shaped much as in Proforeodon and
has the same cordate outline, with acutely pointed and slightly recurved apex ;
it differs, however, in the much better development of the internal cingulum,
which on the posterior half of the crown encloses a shallow fossette. In
Agriochxrus p» is very much as in the Uinta genus, except that it is less com-
pressed and considerably thicker transversely.

Seen from the outer side p2 closely resembles p?, but when looked at
from below or within it is markedly different, for it has a well developed deu-
terocone and is carried upon three fangs. The deuterocone is larger than in
FProtoreodon, and is even more distinct than in Ag7zochwrus, and, as in the latter,
this internal cusp has an asymmetrical position near to the posterior border of
the crown. The fourth premolar is a little shorter antero-posteriorly than p2
or p®, but is broader than either; the deuterocone is now a symmetrically
developed crescent, the apex of which is placed opposite to that of the proto-
cone. In Agriochewrus this tooth is almost molariform, having two external
and in some species two internal cusps, though the postero-internal one
(tetartocone) is always small and sometimes absent. From the simplicity of
p* in the Uinta genus it may be inferred that the corresponding lower tooth
was not molariform, as it is completely in the White River genus.

While the premolars of Protagriocherius are not especially suggestive of

relationship with Agriochwrus rather than with Oreodon, the molars aye pre-

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UINTA SELENODONTS

eminently so. They have the same low, broad crowns, with very concave ex-
ternal crescents, as in the White River type, though they betray their more
primitive character by the presence of the anterior intermediate cusp (proto-
conule), as in Protoreodon, and even in some specimens of Agriochwrus a rem-
nant of this unpaired lobe may be observed in unworn crowns of m3, where it
is represented by a slight elevation on the anterior horn of the antero-internal
crescent. In size the molars increase progressively from m+ to m2, which
is the largest of the series. Between the molars of Protagriochwrus and those
of Protoreodon there is considerable resemblance, but the differences are ap-
parent at the first glance. In the former the external crescents have much
more deeply concave outer faces, while the median ribs upon these faces are
much less conspicuous; the antero-external buttress is larger, heavier, more
rounded, and less compressed, while the median external buttress is penetrated
much farther by the median valley, which thus separates the external crescents
more widely; the postero-external buttress is absent except on m3, where it
is small. The internal crescents are much alike in the two genera, though
in Protagriochwrus their apices are somewhat higher and the unpaired cusp
(protoconule) is somewhat more reduced. In both genera the internal cres-
cents are unequally developed, the front horn of the hinder crescent reaching
to the outer wall of the crown and cutting short the hinder horn of the
anterior crescent.

As already mentioned, the resemblance of these molars to those of Agrio-
cherus is obvious at the first glance, and yet the latter shows a number of
changes from the Uinta type in molar structure. We observe (1) that the
protoconule has disappeared, or rather has become incorporated into the
antero-internal crescent; (2) that the median external buttress has become
more rounded and broader and is more deeply invaded by the median valley ;
(3) that the external crescents have become more deeply concave and their
median ribs have been suppressed, as has also the postero-external buttress of
m2, In brief, the dentition of Agriocherus differs from that of its presumable
predecessor, (1) in the presence of a diastema behind the canine, (2) in the
greater thickness of the premolars and the more complex patterns of p* and
pz and (3) in the slight changes of molar structure which have just been
enumerated. The differences between Protoreodon and Protagriocherus are
sufficiently clear to the eye and yet they are rather difficult to express in
words. For this purpose the figures are more satisfactory than any descrip-

tion.

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UINTA SELENODONTS 103
MEASUREMENTS.

Upper dentition, length C to M-3 . 0.081 Wippeme=ayaleng thy sig a wenuer-tee nL O:007,
“« canine, ant.-post. diam... .0075 OG Dee aiid, 6 4 Bl Gg fo HOLM
< ‘* transverse diameter. .007 coe inolariserieslenothi cure O35

premolar series, length . . .030 some Met wlensthyean ae set ene -OLO
coo e-ilengtheem ag pee es OOSS, GG Misti swatting as Ge .Ol
oe, Beier es qo 60 6 aCe) Se Vi-2wlenothwn ee) ee Ser OlsG
<Se i P-2 awidthy 95 seer vem uel g-OOA'S CON =2eewicl thine yen sameeren OTS
sce JP-syalengthvs. cu) mer 7s ac) <O09 CG Wee Nene G5 6 6 6 soll
ES WGN 6 5 6d cg “on & -e@otah G6 Wise maveldayy 69 yal eo ,O165

Of the skull very little is preserved, only the upper jaws and the occiput,
but from these may be learned facts of some significance. It may be pre-
sumed that the cranium was even longer and the face shorter proportionately
than in Agrviochwrus, for not only is this the general rule in comparing earlier
and later members of the same phylum, but in Protagriochwrus the extremely
short diastema behind the upper canine points to the same conclusion. Prob-
ably the proportions of the cranial and facial regions were very much as in
Protoreodon. The occiput resembles that of the latter genus and also that of
Agriochwrus, being broad ventrally and narrowing much towards the dorsal
side. The basioccipital is wide but tapers anteriorly, and is only moderately
convex, without median keel. The condyles are large and very prominent,
and in shape and proportions almost exactly resemble those of Agriochwrus.
The exoccipitals are broad and form a wide convexity above the foramen
magnum, on the dorsal margin of which they give off two processes, with a
deep cleft between them. The paroccipital process is long and is curved
backward; its anterior face is concave, as though it had partly embraced a
small tympanic bulla; the process stands well in front of the condyle, and
between the two is a large and deep fossa. Another fossa lies upon the side
of the exoccipital, between the condyle and the crest of the inion. The
supraoccipital is concave and its crest is on each side extended into the wing-
like processes which occur in this genus, as in almost all the oreodonts and
agriochcerids. Both the occipital and sagittal crests are very prominent, and
the latter is quite thick and heavy. Only a narrow strip of the mastoid is
exposed upon the surface of the skull, and there is no distinct mastoid process.
The tympanics are not preserved, but it is clear from the shape of the basi-
occipital that they cannot have been so largely inflated as in Agriocherus.

The jugal is relatively stout, especially in the vertical dimension ; trans-

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104
UINTA SELENODONTS

versely it is quite narrow and compressed; the masseteric ridge and surface
are well marked, though somewhat less prominent than in Agriochwrus. The
vertical depth of the jugal gives to the lower rim of the orbit considerable
elevation above the level of the molars, though the alveolar portion of the
maxillary is extremely low. The infraorbital foramen has not quite so anterior
a position as in Agriocherus, opening above the line between p* and p4, while
in the White River genus it lies above the middle of p*. The little that is
known of the skull adds no especial probability to the view that this Uinta
genus is the forerunner of the White River Agriocherus, but, on the other
hand, it does not in any way render that view less likely.

Aside from the hind-foot, the only limb-bone preserved in connection with
the specimen is the patella. This bone is quite different from that of Pro-
toreodon and very like the patella of Agriochwrus, though it is somewhat less
thickened in the antero-posterior diameter and less rugose upon the dorsal
face, differences which are connected with the smaller size of the animal. The
bone is of an elongate, almond-like, shape, broad proximally and tapering to
a blunt point distally. The dorsal surface is regularly and smoothly convex
in both directions, while the surface for the femoral trochlea is obscurely
divided into two facets by a low and broad median ridge. The shape of this
ridge indicates that the rotular trochlea of the femur was wider and shallower
than in Agriocherus. This patella is broader and thinner than that of Pyro-

toreodon, and has a less elevated median ridge upon the femoral surface.

MEASUREMENTS.

Patella, length . : : : 0.025 Patella, maximum width 3 5 0.017

Of the pes (Plate IV., fig. 28) are preserved portions of the astragalus
and calcaneum, the cuboid and navicular, and the second phalanx of one of
the median digits. Of the astragalus we have the proximal half, which differs
in some quite marked respects from that of Protoreodon. In the proportions of
proximo-distal length to transverse breadth the astragalus is not very different
in the two genera, and thus Protagriochwrus has not yet attained the broad,
short, almost hippopotamus-like astragalus of its White River successor. The
proximal trochlea is even more asymmetrical than in Protoreodon, the outer
condyle much exceeding the inner one in size, though not rising so far above
it proximally as in the last-named genus; the intercondylar groove is broader

and more widely open than in the latter, more so even than in Agriochevrus.

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105
UINTA SELENODONTS

The sustentacular facet is very broad proportionately, a point of resemblance
to the White River genus, though its internal border is not so much elevated ;
the external calcaneal facet is more oblique and more deeply concave than in
the latter, and the fibular facet somewhat broader. Though the distal trochlea
is missing, yet the surfaces for it upon the cuboid and navicular show that the
facet for the former was relatively broader than in Protoreodon, approaching
the proportions seen in Agriocherus.

Very little of the calcaneum is preserved, only the distal end with the
fibular facet; this end has upon its external side a broad, deep sulcus, such as
is found in Agriocherus, but not in Protoreodon. The cuboidal facet is no
broader—indeed, is relatively narrower—than in the latter, but has a consider-
ably greater dorso-plantar diameter, and the distal astragalar surface is like-
wise more extended in the same direction. The fibular facet is narrower and
rises higher and more abruptly than in Agvtochwrus and is more regularly
arched, while the proximal astragalar facet is more oblique and forms a sharp
ridge by its junction with the fibular surface. The sustentaculum is badly
broken, but the corresponding facet upon the astragalus shows that it must
have projected more prominently than in Protercodon. Between Agriocherus
and Oreodon we find similar differences; in the latter, as in all the oreodonts,
the sustentaculum projects but very little from the tibial side of the calcaneum,
while in Agrzocherus it is much more prominent.

The cuboid is decidedly lower and broader proportionately than in Pro-
toreodon, though it has not yet become so low, wide, and thick as is the case
in Agriocherus. The difference in this respect between Protagriocherus and
Frotoreodon is much the same as that between their White River successors,
in both of which the tarsal bones have shortened and broadened, but far more
so in Agriochwrus than in Oreodon. The calcaneal facet is quite broad, though
hardly so wide proportionately as in Protoreodon ; it is also less steeply in-
clined than in the latter, but descends farther upon the dorsal face of the bone.
The astragalar facet is broader proportionately than in Protoreodon and of
nearly the same relative size as in Agrzocherus, but its dorsal border rises
higher proximally. On the tibial side of the cuboid are three facets for the
navicular, a large concavity on the plantar border, and on the dorsal margin two
small plane facets separated by a’'deep groove. Of these dorsal facets the distal
one is carried upon a prominence, which also bears a facet for the ecto-cunei-
form. In Agriocherus the plantar facet for the navicular is much the same as

in the Uinta genus, but on the dorsal side is only a single facet for the navicular

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106

and none for the ecto-cuneiform, which has become extremely short proximo-
distally. The distal end of the cuboid is wider and thicker than in Protoreo-
don, and the great hook-like projection from the plantar face is shorter, but
heavier; the facet for the fourth metatarsal is wider, and that for the fifth
larger and more in the same plane with the fourth than is the case in Protoreo-
don. The same is true of Agriocherus, but here the surface for mt. iv. is
relatively more extended in the dorso-plantar dimension.

The navicular is higher and thicker than in Pvotoreodon, though this
appearance of greater height is partly deceptive and due to the elevation of
the dorsal border of the proximal end. The bone is shaped very much as in
the last-named genus, and the only obvious difference is the greater size of
the plantar hook in Protagriochwrus. In Agriocherus the navicular has be-
come much lower and wider, the increase in breadth being principally due to
the widening of the internal portion of the facet for the astragalus, while on
the distal face the surface for the compound cuneiform is more extended
transversely, but less planto-dorsally, and the facet for the ento-cuneiform is
smaller and more sessile.

When the cuboid and navicular are placed in their natural position with
reference to each other, it may be readily seen that the cuneiforms were much
higher in proportion to their breadth than is the case in Agriochwrus. Doubt-
less the meso- and ecto-cuneiforms were coossified, as in all the known oreo-
donts and agriocheerids.

A second phalanx of one of the median pair of digits is relatively longer
and more slender than the corresponding bone of Agviochewrus ; the proximal
end is less distinctly divided into two facets by the less elevated intercondylar
ridge, and the median dorsal beak is much less prominently developed. The
shaft is relatively longer, narrower, and thinner, and tapers more towards the
distal end. The distal trochlea is more like that of Agrviochwrus, being reflected
far over upon the dorsal face of the phalanx and distinctly cleft along the median
line; it differs from that of the White River genus in being relatively narrower.
The second phalanx of the pes in Oreodon is very similar indeed to that of
Protagriocherus, but with a few differences which may ultimately prove to be
significant. Thus the bone is relatively shorter and heavier than in the Uinta
form; the distal trochlea is not reflected quite ‘so far over upon the dorsal side,
and its plantar portion is somewhat less distinctly divided by the median cleft.
In Protoreodon this phalanx is similar, but longer and thinner. Most unfortu-

nately, no unguals have been found in connection with Protagriochwrus, but

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UINTA SELENODONTS

107
from the shape of the second phalanx it may be confidently inferred that the
extraordinary claw-like form characteristic of Agriocherus had not yet been
developed, at least not in any such degree. It would be most important to
learn whether the unguals showed any tendency towards the assumption of
the claw-shape, but this must await future discovery.

In the following table measurements of Protagriocherus annectens and

Agriocharus latifrons are given together for purposes of comparison.

MEASUREMENTS.
Protagriochcerus. Agriochcerus.
Astragalus, length : : : . : 0.031
se width proximal trochlea_. ; -O15 -O17
Calcaneum, width distal end : ; ‘ .006 .007
ee depthyacsdarms F : : .O14 .019
Cuboid, height of dorsal face £ : : .O14 .O14
width . : 0 : 6 : -O125 .O155
thickness : : : : : -O16 .023
Navicular, height : : : : ; -O10 -009
Gc width . , 3 5 : .O1l .O17
thickness . : : : : .O17 .O21
Second phalanx, length : : ; ; .O17 .O17
ae Go width proximal end . . -009 -0095
oe «« distal end d ¢ -0075 .008
gs thickness proximalend . -008 -010
UG es se distal end . 5 -0075 -008

The single species of Protagriochwrus at present known may be called
P. annectens, sp. nov., and in the absence of other species with which to com-
pare it its definition can be formal only. This may be taken, first, from the
size as given in the various tables of measurements, and, secondly, from the

simplicity of the premolar teeth.

The Taxonomic Position of Protagrtocherus.

This genus is not yet sufficiently well known to render its systematic
position and its phylogenetic significance clear, though what little we already
know concerning it is highly suggestive. The dentition, and especially the
upper molars, leads us almost irresistibly to the conclusion that Protagrio-
cherus is ancestral to Agriochwrus, and this conclusion is further confirmed by
the character of the tarsus. This differs from that of Protoreodon in very
much the same way as the tarsus of Agriochwrus differs from that of Oreodon.

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108

In each instance the Uinta genus has a higher and narrower tarsus than its
presumable White River successor.

Certain difficulties which oppose the phylogenetic arrangement here
sketched, deriving Agvrzocherus from Protagriocherus, suggest themselves,
though they seem to be of no very great weight. (1) The difference between
the two genera is apparently greater than that between Orcodon and Protoreo-
don, or that between Poebrotherium and Protylopus, and therefore it might seem
that the structural gap is too great for the time interval. Asa matter of fact,
however, we know that development has proceeded at different rates in different
phyla, and there is no known reason why change in the agriochcerids should
not have been rather more rapid than in the oreodonts. (2) The lack of
diastemata in the dentition of Protagriochwrus and their presence in the White
River genus might by some be regarded as an insuperable objection to the
derivation of the latter from the former. As shown in a previous chapter, this
is an untenable assumption; Proty/opus has no diastemata, in Poebrotherium
they are very short, but in Gomphothertum and all the subsequent genera of the
camels they are long. What has happened in the camel series may equally
well have happened among the agriochcerids. (3) It would naturally be ex-
pected that the very remarkable foot-structure, and especially the ungual
phalanges of Agriochewrus, should be more distinctly foreshadowed in its Uinta
ancestor. So far as the tarsus of Protagriocherus is concerned, it is just what
it should be in the ancestral form, and until the ungual phalanges have been
recovered we shall not know how great the difference between the two genera
in this respect really is.

The available evidence thus goes to show that Agriocherus is the descend-
ant of Protagriochwrus, or of some very similar type, and that for all practical
purposes the latter may serve to represent the actual ancestor. If this con-
clusion be valid, then certain interesting and somewhat unexpected corollaries
will follow from it. (1) The oreodonts and agriochcerids are very closely
related, and the marked differences displayed by the White River and later
representatives of the two families were due to a rapid divergent evolution,
especially on the part of the Agriochwride. In the latter family the skull
retained most of its primitive features, such as the elongate cranium, open
orbits, convex lachrymals, etc., though with an elongation of the muzzle and
consequent production of moderate diastemata in the dentition. The teeth
underwent a curious modification, while the limbs and especially the feet

assumed a most extraordinary character, quite unique among the artiodactyls,

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109
UINTA SELENODONTS

large compressed claws taking the place of the hoofs. In the oreodonts, on
the other hand, the cranium was somewhat shortened, the orbit became closed
behind by the union of the postorbital processes from the frontal and jugal,
and a deep pit appeared on the lachrymal; the molar teeth assumed a tetra-
selenodont pattern much like that of the modern deer, while the skeleton of
the trunk, limbs, and feet underwent comparatively little modification, and
even in long subsequent periods the changes in the skeleton never were
extreme or radical.

Although the White River members of the oreodonts and agriochcerids
had thus become widely separated, the Uinta representatives of the two fami-
lies were still very close together, and, were it not for their subsequent history,
no one would hesitate to include them all in the same group. Not only are
FProtoreodon and Frotagriocherus very much alike in all known parts of their
structure, but the former even has a great deal about it to suggest relationship
with Agriocherus, and it lacks but comparatively little of being itself the
common ancestor of both families. The skull is of a pattern from which both
the oreodont and the agriocheerid type might readily be derived, as is also the
dentition, save only the upper molars. The latter seem to have already pro-
gressed too far in the direction of the true oreodonts to be ancestral to the
curious upper molars of Agriocherus. The lower molars, on the contrary,
are very much like those of the White River genus. The feet also would
appear to have undergone changes in the same direction and away from the
primitive condition which was common to the two families.

The connection between the two Uinta genera becomes all the closer
when the various species of Protoreodon are studied with reference to this
point. The species which I formerly called Agrtotherium paradoaxicum, and
which I regarded as probably ancestral to Agriocherus, tends to bridge the
gap between Protoreodon and Protagrioche/us, and, indeed, stands almost mid-
way between the two genera. I said of it: “The differences between Pro-
toreodon and Agriotherium are such as strongly to suggest the inference that,
while the former is the ancestor of the oreodonts, the latter stands in a similar
relation to the agriochcerids. This determination can at present only be pro-
visional until more is learned concerning the foot-structure of the present
genus. At all events, if Agriotherium be not the desired ancestral form, we
may feel confident that that form when found will prove to be of a very similar
character.” (’98, p. 80.) The discovery of Protagriocherus renders it highly
probable that this genus is the “similar form” sought for and is the actual

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ancestor of Agriocherus, and that Protoreodon paradoxicus is merely a connect-
ing link between the former and the oreodonts. Its structure thus tends to
confirm the conclusion that the two families have a common origin, and that
the numerous points of resemblance between them are not simply instances of
parallel development.

(2.) If these conclusions are well founded, it follows that the likeness of
the upper molars of Agriochewrius to those of the anthracotheres—a likeness to
which attention has repeatedly been directed—is not due to any near relation-
ship between the groups, but has been independently acquired. The molars
of Protagriocherus, despite the presence of the fifth cusp (protoconule), are less
like those of Ancodus than are the molars of its White River successor. The
peculiar arrangement of the incisors, canines, and caniniform lower premolars,
which is so highly characteristic of the agriochcerids and oreodonts, is already
fully established in the Uinta genera of these families. Consequently, to find
a common ancestor of the agriochcerids and the anthracotheres (in which the
canines are normal), we should have to go very far back indeed, so far that the
peculiar features of the anthracothere dentition would probably not yet have
begun to appear.

(3.) As we cannot yet point out the Bridger ancestor of the oreodonts,
of course it is not yet possible to identify the common ancestor of both fami-
lies. However, from the close approximation between Proforeodon and Pro-
tagriocherus, it is altogether probable that the common ancestral form will be
found in the Washakie or the Bridger proper. It is further probable that this
unknown genus will prove to be very nearly related to the forerunners of Pro-
uilopus, Leptoreodon, etc., and may perhaps even be a member of the same
family. Further than this it is unsafe to speculate, for the interrelationships
of the various Uinta selenodonts are very complicated and difficult to unravel,
their likenesses and unlikenesses being combined in such puzzling ways, but
the peculiarities of the canines and premolars would indicate that Leptoreodon
and Camelomeryx lead back to this common ancestor of the oreodonts and
agriochcerids, and that this ancestor, while very nearly allied to the forerunner
of Protylopus, was yet in Bridger times generically distinct. To those who
are familiar with the remarkable appearance of Agrzochawrus, with its extra-
ordinary clawed feet, it may seem altogether unlikely that this genus can have
been derived from a Bridger ancestor, common also to the oreodonts. When,
however, Agriochewrus is carefully studied, every portion of its skeleton, not

even excepting its extraordinary feet, is found to bear witness of its relation-

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UINTA SELENODONTS

ship to the oreodonts. The Uinta representatives of the latter family are still
more like Agriocherus and materially diminish the gap between the two
groups. Even though Protagriocherus should eventually prove not to be the
direct ancestor of Agriocherus, it certainly tends to approximate the two
families very closely and to render it entirely probable that both were derived
from a common Bridger ancestor. That this hypothetical ancestor was in its
time nearly allied to the forerunner of Proty/opus, and still more so to that of
Leptoreodon, seems also very likely, whence follows the further probability that
the Oreodo:tide and Agriocheride, \ike all the other indigenous North Ameri-
can selenodonts, should be referred to the Tylopoda.

SUMMARY AND CONCLUSIONS

1. The American Tertiary Selenodonts form two distinct assemblages :
first, those derived by migration from the Old World, and, second, the truly
indigenous forms. The former includes the anthracotheres and the true
ruminants, while the latter has the oreodonts, agriochcerids, the Leptomerycide,
and Camelde.

2. The Uinta fauna is the oldest American horizon in which the seleno-
donts are numerous and conspicuous.

3. The study of these Uinta selenodonts strongly suggests that all the
indigenous American forms are nearly related and should all be referred to
the Tylopoda.

4. The Tylopoda are a highly diversified group, filling in America the
place taken in Eurasia by the Pecora and Tragulina, which they parallel in
many ways.

5. The Uinta beds are confined to the basin south of the Uinta Mount-
ains, where they overlie the upper Bridger (Washakie); they are divisible
into two horizons (B and C), of which the lower is transitional from the
Washakie. Apparently there is an unconformity between B and C.

6. The Uinta is to be correlated with the Lutetian of France, and belongs
to the uppermost Eocene or lowest Oligocene.

7. Leptomeryx, a White River genus, retains some of the upper incisors,
but not the canine; the lower canine is incisiform and pz caniniform, but
much reduced in size. The premolars are compressed and trenchant, but

complicated by internal cusps; the molars are very brachyodont and have a

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UINTA SELENODONTS

general resemblance to the tragulines, but the upper ones have remarkably
prominent external buttresses and a development of the inner crescents which
is much more tylopodan than traguline. The skull,as newly discovered speci-
mens show, is very tylopodan in character, resembling that of a miniature
Poebrotherium, though with small and hollow tympanic bulla, and the angle
of the mandible is less produced. The neck is short, the odontoid process
peg-shaped, and the vertebrae of the normal, not cameloid, type. The loins
are long and much curved and the tail short. The fore-limb is short and
slender; the scapula and humerus resemble those of Poebrotherium, but the
ulna and radius are separate. The trapezoid and magnum are codssified
and the lunar so shifted as to rest almost entirely upon the unciform. The
manus has four complete digits, though the lateral pair are greatly reduced.
The hind-limb is long; the pelvis and femur are tylopodan; the fibula is
reduced to a proximal spine and distal malleolar bone. The navicular and
cuboid are coossified. A posterior cannon-bone is formed, of characteristi-
cally tylopodan shape; the lateral metatarsals are short splints.

8. Leptomeryx should be referred ta the Tylopoda.

9. Hypertragulus (White River and John Day) is much like Leptomeryx,
but with many differences of detail; it has retained the canines in their
original form and function and has simple premolars. The skull is very
tylopodan, with abruptly contracted muzzle, which is shorter than in Leffo-
meryx, and the angle of the mandible is much more produced, The fore-limb
is like that of the latter genus, but the ulna and radius have coalesced, while
there is no cannon-bone in the pes.

10. Hypertragulus is even more obviously related to the Camelde than
is Leptomeryx.

11. Hypisodus (White River) is remarkable for its prismatic molars and for
the conversion of the lower canine and first premolar into functional incisors.

12. Protoceras (White River) has lost the upper incisors but retained a
canine, which in the male is tusk-like and opposes a caniniform pz. The
molars are like those of Leftomeryx and Poebrotherium, as are also the pre-
molars, except for their greater elongation. The skull is of less distinctly
tylopodan form than in the preceding genera, and in the backward shifting of
the orbits and the bending downward of the face upon the cranial axis it
resembles that of the higher Pecora. The nasals are very much shortened,
and in the male great bony protuberances rise from the parietals, frontals, and

maxillaries. The neck is of moderate length, the axis has a flattened odon-

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UINTA SELENODONTS 3

toid, and the other cervicals are of normal structure. The limbs are much
like those of Leptomeryx and Poebrotherium ; the ulna and radius are coossi-
fied, the trapezoid and magnum separate, and the manus tetradactyl. The
fibula is completely reduced, the cuboid and navicular distinct, and the pes
didactyl, but without a cannon-bone.

13. LProtoceras is clearly related to Leptomeryx, and if the latter is referred
to the Tylopoda, the former must likewise be so classified.

14. Protylopus (Uinta) has an undiminished dentition without diastemata,
but with the canines of very small size. The teeth are extremely like those
of Poebrotherium, but less elongate and more brachyodont. The skull is also
extremely like that of Poebrotherium, but has a less elongate muzzle, less
capacious cranium, and a small tympanic bulla, free from cancelli; the coro-
noid process of the mandible is more ruminant-like. The thoracic, lumbar,
sacral, and caudal vetebre resemble those of Poebrotherium, as does the fore-
limb, the ulna and radius showing incipient coalescence in old individuals ;
the manus is, however, tetradactyl. Pelvis, femur, and tibia are entirely tylopo-
dan; the fibula is uninterrupted but with extremely slender shaft. In the pes
the lateral metatarsals are elongate, filiform splints.

15. FProtylopus seems almost certainly to be the direct ancestor of Poe-
brotherium, and thus the most ancient known member of the Camcelde.

16. A closed dentition does not necessarily imply that the animal is
capable of no further development.

17. The very small canines in Protylopus and Poebrotherium, and their
gradual enlargement in Gomphotherium and the subsequent genera of the
phylum, indicate that structures may first be reduced and then enlarged in a
phyletic series, while the elongation of the premolars in Poebrotherium and
their reduction in the later genera show that structures may first be enlarged
and then reduced.

18. Leptotragulus (Uinta) is very imperfectly known; its mandibular
dentition is very much like that of Poebrotherium, but appears to differ from it
in the suppression of p; and the large size of the canine.

19. Leptotvagulus may, when better known, prove to be the ancestor of
Fypertragulus.

20. Leptoreodon (Uinta) has an unreduced dentition, with small, conical
upper incisors, a stout D-shaped upper canine, and diastemata between p. I and
p.2. The lower canine has become incisiform and p; caniniform, as in the oreo-
donts; the upper premolars are simple and the molars composed of four cres-

8

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114
UINTA SELENODONTS

cents like those of Protylopus, which they closely resemble, except that the
outer crescents are more concave and the outer buttresses more prominent.
The lower premolars, except the caniniform p; and the compressed-conical
pz, have large inner cusps. The skull is quite like that of Protylopus, but
somewhat more massive and with a more elongate muzzle. The cervical
vertebre are of moderate length and the odontoid process is sub-conical,
but broad and blunt; the neural spine of the axis is a very large plate. The
lumbar vertebree are heavy, with large and nearly straight transverse pro-
cesses. The bones of the fore-limb are intermediate in character between
those of the oreodonts and those of the Camelde, and the ulna and radius are
not anchylosed at any point. The carpus is quite like that of Leptomeryzx,
but the lunar rests almost equally upon the magnum and unciform. The
manus is tetradactyl and resembles that of Protylopus, but the lateral meta-
carpals are less reduced and the median pair less enlarged. The pelvis, femur,
and tibia. are much like those of Protylopus, but the cnemial crest of the latter
is far less prominent. The fibula has a very slender shaft, though it is not
filiform, as in the last-named genus. The pes has a general resemblance to
that of Protylopus, but the lateral metatarsals are not nearly so much reduced.

21. Leptoreodon may be regarded as the probable ancestor of Protoceras.

22. Camelomeryx (Uinta) has a dentition like that of Leptoreodon, except for
the smaller upper incisors, which are reduced to two. The skull also resembles
that of the latter genus, but has a narrower and less capacious brain-case,
deeper postorbital constriction, and much longer sagittal crest, and the orbit is
quite far forward. The skull is much like that of Leptomeryx. Limb-bones
referred, though with some doubt, to this genus show an anchylosed ulna and
radius; the tetradactyl manus is much like that of Leptomeryx, but the lunar
rests largely upon the magnum, which is separate from the trapezoid, and the
lateral metacarpals are less reduced. The pes resembles that of Protylopus,
and has enlarged median and much reduced lateral metatarsals.

23. Thetaxonomic position of Camclomeryx is somewhat doubtful, though
it is probably a form nearly allied to the ancestor of Lep/omeryx, if not itself
that ancestor.

24. Oromeryx (Uinta) has no diastemata in the dentition, and in the
upper molars, especially m*, the posterior half of the crown is narrower than
the anterior half. The systematic position of this genus is quite uncertain.

25. Bunomeryx (Uinta) is interesting as tending to show that the postero-

internal crescent of the tylopodan upper molar is not the hypocone but the meta-

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115

conule, an interpretation confirmed by the asymmetrical shape of these teeth in
many Uinta selenodonts. Azmonzeryx is evidently descended from the Bridger
Ffomacodon and should be referred to the Homacodontide, a family which seems
to bear the same relation to the Tylopoda as the Dichobunide@ bear to the Pecora.

26. Protoreodon (Uinta) is already a true oreodont, the family being dis-
tinctly differentiated as such in the Uinta. The dentition resembles most that
of Oreodox and is without diastemata, the lower canine being incisiform and p;
caniniform. In some species the upper incisors are reduced to two or even to
one. The premolars are somewhat simpler than in Oreodon, and the molars
broader and more distinctly brachyodont; the upper molars retain the fifth
cusp (protoconule), and the lower molars are very like those of Agriocherus.
The skull is also like that of Oreodon, but resembles that of Agriochwrus in
the narrow, elongate cranium, the incompletely closed orbit, and the absence
of a lachrymal pit. The vertebral column and limbs differ from those of
Oreodon only in minor details. In the carpus the lunar has shifted less com-
pletely upon the unciform and the pollex is somewhat larger. The pes is
almost exactly like that of the White River genus, except for a rudiment of
mt. i. attached to the ento-cuneiform.

27. The genus Protorcodon seems to include two lines of development,
one represented by P. farvus and leading to the later oreodonts, the other
composed of species with reduced upper incisors, which became dominant in
the true Uinta beds, but seems to have died out without descendants.

28. The Oreodontide probably should be considered an offshoot of the
Tylopoda.

29. Hyomeryx is distinguished from Protoreodon by the absence of upper
incisors and by the less concavity of the external crescents of the upper molars.

30. Protagriocherus has a dentition much like that of Protoreodon, but
with somewhat more complex upper premolars, and molars with much more
concave external crescents and less prominent median ribs, and the external
median buttress is penetrated farther by the median valley. The skull, which
is very imperfectly known, seems to agree with that of Protorcodon, The
tarsus has considerable resemblance to that of Agriocherus, and though not
so broad and short, is much more so than in Protoreodon.

31. Protagriocherus is not sufficiently well known to make its taxonomic
position clear, but it seems to be the ancestor of Agriocherus.

32. The Agriocheride are probably nearly related to the Oreodontide, and

derived from a common Bridger ancestor, and if so, they are aberrant Tylopoda.

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116

The conclusion that all the indigenous North American selenodonts are
members of the suborder Tylopoda, though by no means demonstrated, seems
to be naturally deducible from the evidence as we now have it. At all events,
this hypothesis explains better than any yet suggested the complicated tangle
of resemblances and differences between the various American groups, as well :
as those between the American and the European families. In the European
Dichobunide and the American Homacodontide the Pecora and the Tylopoda
nearly approximate to a common term, if they do not actually merge. TZ7igo-
nolestes, or some similar form, may be the common ancestor of both.

Of the numerous phylogenetic lines included within the tylopodan sub-
order, only one—that of the Camelde proper—has persisted to the present
day. The current definition of the suborder Tylopoda has been drawn from
the peculiarities of the later members of this single family, and hence it is too
narrowly restricted to embrace the great group of related selenodont families
which flourished so abundantly in the Upper Eocene and Oligocene of North
America. Indeed, so diversified is this group, that it is exceedingly difficult
to frame a definition of the suborder that shall be diagnostic of it—on the one
hand, embracing all its members, and, on the other, clearly distinguishing it
from the Pecora and Tragulina. The difficulty arises not only from the lack
of obvious characteristics which are common to all members of the Tylopoda,
but also from the numerous features in which one or other member of the
suborder has developed in a course parallel with that of the Pecora or the
Tragulina. This difficulty of definition, however, is the inevitable result of
the discovery of long and clearly marked phylogenetic series. One by one
the characteristics of the terminal members of the series disappear as the line
is traced back, and are replaced by more generalized features, which are
repeated in many other groups. However obvious may be the relationship
between a number of highly diversified families, the difficulty of expressing
that relationship in a definition increases with the length and completeness of
the phylogeny, because of the structural differences between the earlier and
later members of the series.

In the Tylopoda the peculiarities of the cervical vertebre, for example,
are found only in the main line of descent, the Camelid@, and seem to be cor-
related with the elongation of the neck. The reduction of the ungual pha-
langes to nodular form and the cancellous structure of the tympanic bullz
are also confined to the same line, and were evidently acquired within the

limits of the family. In Poebrotherium and Protylopus the phalanges are of

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117
the normal selenodont type, and in the latter the tympanic is hollow. The
form of the cannon-bone, when present at all, is characteristic, but, except in
the pes of Leptomeryx, the metapodials are not codssified in any of the Eocene
or Oligocene genera. In all members of the suborder, without exception, the
metapodial keels are confined to the palmar (or plantar) aspect of the bones,
but this is equally true of the Tragulina and the earliest Pecora (e.g., Gelocus),
The cuboid and navicular are separate in all the genera except Leptomeryx,
Hypertragulus, and Hypisodus, as are also the trapezoid and magnum, except
in Leptomeryx, and perhaps the other two genera, while in the entire series
from the Wasatch onward (assuming that Ziigonolestes is properly referred to
this phylum) the meso- and ecto-cuneiforms of the tarsus are coalesced. The
digital formula varies between V-V and II-II.

The molars are brachyodont, save for a moderate degree of hypsodontism
in the later members of the Camelde. The premolars are simple, trenchant,
and often elongated, but in the more modern Camelde they become much
reduced in size and number. Incisors and canines are usually present in their
full number, but Leptomeryx has lost the upper canine and Protoceras all the
upper incisors, which in the Camelde are also reduced, though not entirely
suppressed. Except in the main line of the suborder, a very frequent charac-
teristic is the conversion of the lower canine into a functional incisor, while
the place of the canine is taken by py. More or less obvious indications of
this may be seen in the oreodonts, agriochcerids, Lepéoreodon, Camelomeryx,
Protoceras, and Leptomeryx, and the condition in Protylopus seems to indicate
a tendency in the same direction, but the tendency was checked and the true
canines were again enlarged.

It is in the structure of the skull that we find the most characteristic
tylopodan features and those which are most constant throughout the sub-
order. Rutimeyer’s summary needs but little change to apply to the newly
discovered forms as well as to those which have long been known. The pre-
maxillaries are very complete and reduced only by small incisive foramina.
Nevertheless, the skull is distinguished by the very rapid tapering of the face
anteriorly, which is expressed particularly in the triangular form of the palate
and in the very oblique position of the molar series. The maxillary region
of the skull is peculiarly limited, and mainly taken up in the formation of the
nasal passage, having but a low alveolus and very limited muscular surfaces.
Even the jugal, as well as the lachrymal, takes almost no share in the forma-
tion of the face. The infraorbital foramen lies far back, above the last pre-

TRANSACTIONS OF WAGNER
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118

molar; there is no masseter crest and the masseter surface is almost obsolete.
The nasal canal is high and roofed over by short nasals; the posterior nares
are also high, especially in the pterygoid portion. Characteristic in the
cranium is the small extent of the frontal zone as compared with the parietal
zone, in the formation of which the very high squamosals take a large share.
The orbits are very prominent. A consequence of these relations is the dis-
placement of the orbits into the facial region above the molar alveoli, and the
extraordinary length of the temporal fossa. Sagittal and occipital crests are
prominent. The glenoid cavity is small, but has a high postglenoid process,
and very generally the angle of the mandible is produced behind the condyle.

The applicability of this description is least obvious in the case of Proto-
cevas, in which genus the skull is much modified, approximating it in some
respects to the Azgher Pecora, the Cavicornia. ‘This is to be seen in the edentu-
lous premaxillaries (though the incisive foramina remain quite small), in the
shifting of the orbit behind the molar alveoli, and in the downward bending of
the face upon the cranial axis, the latter not recurring in any other member
of the Tylopoda. Further, the angle of the lower jaw is not produced into a
hook-like process behind the condyle. In spite of these deviations, the essen-
tial features even of this skull are manifestly in agreement with those of the
other Tylopoda.

At the other extreme of the scale stands the skull structure of the Oreo-
dontide and Agriocheride, but in these cases also the definition will apply.
These families both retained throughout their history a very primitive type of
skull, which gives quite a close and deceptive resemblance to that seen in the
anoplotheres and anthracotheres.

In two respects the skull in the main phylum of the Tylopoda differs
from that of all the side branches; namely, in the form of the mandibular
condyle and in the cancellous structure of the tympanic bulla. The history
of this phylum shows, however, that both of these peculiarities were acquired
after the family Camelide had begun its separate existence. Even in Poe-
brotherium the condyle is still transverse and displays little tendency to assume
the spheroidal shape, while in the earlier genus Protylopus the auditory bulla
is small and free from cancellous bone. Were the cervical vertebree of the
latter genus known, we should probably find that the extraordinary peculiarities
of these vertebrze were likewise acquired within the limits of the family.

The study of the Uinta selenodonts teaches us very forcibly the im-

portance of giving due weight to zodgeographical considerations in dealing

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119
UINTA SELENODONTS

with problems of relationship. It was considerations of this kind that first
suggested to me the probability that Proteceras must in some way be related
to Leptomeryx and its allies,a suggestion which now seems to be very strongly
confirmed by the discovery of the new selenodonts from the Uinta beds.
Migrations of terrestrial mammals have, of course, repeatedly taken place
from one continent to another, as is amply demonstrated by the successive
fossil faunas of Europe and North America, but the native stocks are apt to
maintain their footing for long periods of time against the invasion of nearly
allied forms which play similar parts in nature. It is curious to observe how
long a time was required before the Pecora were able to establish themselves
in North America. Not until they had reached a very high plane of organiza-
tion did they succeed in overcoming the competition of the highly diversified
Tylopoda, which had been developed here and which were not entirely driven
from this continent until late Pleistocene times. In South America they still
continue to flourish, and in that continent the only representatives of the
Pecora are the deer in limited variety.

In cases of doubtful affinities the probabilities are usually in favor ot
reference to an indigenous group, for they almost always outnumber the
immigrant forms, and it is with such indigenous groups that the most careful
comparisons should be made. Neglect of this principle has led most students
of the American selenodonts astray.

These considerations emphasize once more the necessity of obtaining long
and fairly complete phylogenetic series for the satisfactory solution of taxonomic
problems. Without such series it is exceedingly difficult, often impossible, to
escape being deceived by resemblances due to parallel or convergent develop-
ment. With these series, such deceptive resemblances may be exposed and
allowed only their due weight, while puzzling differences may be followed out
in their origin and development and given their proper taxonomic value.

This paper contains the recantation of many opinions which I formerly
maintained concerning the relationships and systematic position of the various
groups of peculiar North American selenodonts. I may say, however, that
these opinions were not very confidently held, for they never seemed to ex-
plain satisfactorily the manifold peculiarities and the isolated position of these
families and genera. It may be that the views here expressed are destined to
have no longer life, but they do offer a much more satisfactory solution of the
problem, and they are at least founded upon a much wider range of evidence
than has been available hitherto.

TRANSACTIONS OF WAGNER
UINTA SELENODONTS

The subjoined table exhibits the relationships of the various genera as

conjectured in the preceding pages.

3
‘ZS 5
=
Protoceras Beds. o 38 8
2
“4 ~
fH A a
3 E
; 4 = S
3 f > OS
= B ia
WHITE RIVER. 4 Oreodon Beds. 8 5 2 aS, g 4
oO cS gS iS) a i) 2
ro) fo} a} = Om Q ro)
nest Oo Te] [ov Q, oy O
H a Nn o a cal i)
oy o) oo 4 ea} q Ay
Titanotherium Beds.
|
|
|
2 Z l
AH mp Ra ES}
g gS Tee as S
vE Ome o fF bn
UINTA. 9 3 & 3 8 Z Bs E
‘o Sn ES One fa es =
ly O HH ev So Me 5 Qi
el 8) pe pam ~ = o Per] [o}
3 fe) / SoS O a, rs
cS S| per od Pe >
° oC my fs lS ® £
oo i | & a m 4 i
me ) | (S) oe) ao fay
| | a ie, Wa
\ | | /
Ni] /
\/
\/ /
2 75 = .
BRIDGER. ? Homacodontide.

WASATCH. ? Trigonolestes.

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121
UINTA SELENODONTS

GOPE, VED eeaess:

“ce “ea "89.
LEIDY; us 109:
MARSH O23. G5) 27,72

ss a "94.
Osporn, H. F., '95.
RUTIMEYER, L., 83.

SCHLOSSER, M., '87.

Scott, W. B. . ’89.

‘ "gle
oe ae 94.
oe ‘ 95a

Ee = hte

WoRTMAN, J. L., 98.

952.

PIPE WAT URE

The Artiodactyla. Part I. American Naturalist, vol, xxii.

The same. Part II. J0zd., vol. xxiii.

The Extinct Mammalian Fauna of Dakota and Nebraska, Phila-
delphia, 1869.

The Introduction and Succession of Vertebrate Life in America.
American Journal of Science and Arts, Third Series, vol. xiv.

A Horned Artiodactyle from the Miocene. Zézd., vol. xli.

Description of Tertiary Artiodactyles. /ézd¢., vol. xlviii.

Fossil Mammals of the Uinta Basin. Budletin American Museum
of Natural History, vol. vii.

Beitrage zu einer natiirlichen Geschichte der Hirsche. Abth. iii.
Abhandlungen d. schwetscr. paleontol, Gesellsch., Bd. x.
Beitrage zur Stammesgeschichte der Hufthiere. AZorphologisches

Jahrbuch, Ba. xii.
The Mammalia of the Uinta Formation. Part Il. 7yransactions

American Philosophical Soctety, New Series, vol. xvi.

. Beitrage z. Kenntniss d. Oreodontidee. Alorphologtsches Jahrbuch,

Bd. xvi.

. The Osteology of Poebrotherium. Journal of Morphology, vol. v.

. The Osteology of Mesohippus and Leptomeryx. /ézd., vol. v.

The Mammalia of the Deep River Beds. Zyvansactions American
Philosophical Society, New Series, vol. xvii.

. The Structure and Relationships of Ancodus. Journal Academy

Natural Sciences, vol. ix., part iv.

The Osteology and Relations of Protoceras. /ournalof Morphology,
vol. xi.

Preliminary Note on the Selenodont Artiodactyls of the Uinta
Formation. Proceedings American Philosophical Society, vol.
XXXVIl.

The Extinct Camelidzee of North America and some Associated
Forms. Bulletin American Museum of Natural History,

vol. x.

EXPEANATION, OF Wie rie Ades

PAVE Ie

Lepltomeryx evanst. Skull, from the left side. C., lower canine.

Leptomeryx evanst. Distal end of posterior cannon-bone.

fy pertragulus calcaratus. Skull, from the right side. (Drawn from specimens
in the American Museum of Natural History.)

tly pertragulus calcaratus. Skull, top view.

(All figures of natural size.)

qq

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VOL NI. . Pl

Lith. Werner & Winter, Frankfort 9M.

(ay JO

Gaels
elds

On

PLATE Il.

Protylopus petersoni, Skull, from the right side.

Protylopus petersont. Upper molars and premolars of right side, crown view.

Protylopus petersont, Lower molars and premolars of right side, crown view.

Protylopus petersoni. Left pes, front view.

Protylopus petersoni. Left manus, front view. JZ, magnum; U., unciform.

Leptoreodon gracilis. Skull, from right side. / z, first premolar ; ~ 2, second
premolar.

Leptoreodon gracilis, Upper dentition of right side.

Leptoreodon gracilis. Lower dentition of right side. C., canine; 7 3, lateral
incisor ; # Z, caniniform first premolar.

Leptoreodon gracilis, Right manus. Sc., scaphoid; #., radius.

Leptoreodon gracilis. Left pes, front view.

(Ad figures of natural size.)

ecu TRANS. WAGNER FREE INSTITUTE OF SCIENCE:
MI. Pl

Lith. Werner & Winter, Frankfort “M

sedis
ig. 16.

iS)

eo

PLATE Ill.

Camelomeryx longiceps. Skull, from left side.

Camelomeryx longiceps. Right upper dentition. C., canine; # 4, fourth pre-

molar.

? Camelomeryx longiceps. Left manus. Sc., scaphoid; P., pyramidal. Collec-
tion of American Museum of Natural History. (No. 2070.)

? Camelomeryx longiceps. Left pes. Collection of American Museum of Natural
History. (No. 2070.)

Protoreodon parvus. Skull, from right side.

Protoreodon parvus. Left upper dentition, crown view.

Protoreodon parvus. Right carpus. Sc., scaphoid; /., pyramidal; U., unci-
form.

Protoreodon sp. Left pes. Collection American Museum Natural History.

Protoreodon minor, Left upper dentition, crown view.

(All figures of natural size.)

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PLATE IV.

Fig. 24. Protoreodon paradoxicus. Skull, from left side. (Depressed by crushing.)
Fig. 25. Protoreodon paradoxicus. Left upper dentition.

Fig. 26. Protagriocherus annectens. Right upper dentition, side view.

Fig. 27. Protagriocherus annectens. Right upper dentition, crown view.

Fig. 28. Protagriocharus annectens. Left tarsus. V., navicular; Cé., cuboid.

Figures 26, 27, 28 are of the same individual, belonging to the American Museum of

Natural History. (No. 1818.)

(All figures of natural size.)

TRANS. WAGNER FREE INSTITUTE OF SCIENCE.

Lith. Werner & Winter, Frankfort YM.

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