LEONTINIDAE
This family was established to include a group of large, heavily built
ungulates, not unlike rhinoceroses in form, which have rooted teeth,
the molars being similar to those of _Rhinchippidae_, _i. e._, composed
of a wall and an anterior and posterior lobes, but with the cristae
either lacking or little developed; and with the second upper, and the
third lower incisors developed into tush-like caniniform teeth. Two
genera are especially abundant, _Leontinia_ of the Deseado beds, and
_Colpodon_ of the Colpodon beds, the former with the formula
3 1 4 3
-------,
3 1 4 3
the latter with
3 0 4 3
-------.
3 0 4 3
In many ways, the family suggests _Nesodontidae_, and undoubtedly
belongs to that series, if not directly ancestral. The lower molars are
distinctly of the same type as in all the other toxodonts, but show a
tendency to become hyposodont.
The following genera have been assigned by Ameghino to the family. Some
of them are based on very scant material and I have ventured to suggest
in each case what disposition I have felt to be the proper one.
=Leontinia=, the type genus, is described in detail on pages 109-115.
=Scaphops= is based on a mandibular symphysis, which is wider than
usual for _Leontinia_, and on a second upper incisor which is
compressed. The species in the genus _Leontinia_ show a marked degree
of variability, and I can see in this only individual variability, so
that I place _Scaphops_ under _Leontinia_ and _S. grypus_, as a synonym
of _L. gaudryi_.
=Steniogenium= is based on a mandibular symphysis with roots only of
the teeth. The incisors are proclivous and inc. 3 small. I consider
this also as _Leontinia_, and the species _S. sclerops_ as a synonym of
_L. oxyrhynca_, which I think is the female of _L. gaudryi_.
=Ancylocoelus= is a valid genus, differentiated by its dental formula
3 0 4 3
-------,
3 0 3 3
the loss of the upper canine and the lower canine and first premolar
distinguishing it from either _Leontinia_ or _Colpodon_.
=Rodiotherium= is based on a mandibular symphysis which would indicate
an animal with the same formula as the foregoing genus, differing only
in that lower incisor 3 is large. This, to my mind, does not make a
generic character, and at most the species, _R. armatum_, can only be
considered an independent species belonging to the genus _Ancylocoelus_.
=Loxocoelus= is a very questionable genus, based simply on an upper
molar, which “is similar to that of _Homalodontotherium_, but more
squared.” I feel that in regard to this genus it should stand as
unknown until more material is found.
In our collection, over twenty skulls and jaws belonging to this family
turned up, but all clearly belong to two types, the typical _Leontinia
gaudryi_, and some others in which the caniniform teeth are not so
well developed, which are either _L. oxyrhynca_ or, as I believe, the
females of _L. gaudryi_. It is this uniformity of the material which
leads me to doubt the validity of the considerable number of genera
which Ameghino has established, for I found on sectioning the teeth
that between the little worn crown and the much worn one there was
a marked difference in the appearance of the infoldings and in the
development of the pits.
=Leontinia= Ameghino
Leontinia Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 647.
Leontinia Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 469.
Scaphops Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 475.
Steniogenium Amegh., 1895, Inst. Geog. Argen., t. 15, p. 654.
Steniogenium Amegh., 1897, Inst. Geog. Argen., t. 18, p. 475.
Colpodon Gaudry, in part, 1906, Anal. Palaeontologie, t. 1, p. 30.
The formula is
3 1 4 3
-------;
3 1 4 3
type species _L. gaudryi_. Of all the animals in the Deseado, this
is the most abundant. Using this species as a basis, the following
are the characteristic features. The first upper incisor is a small
cropping tooth, with a well-developed cingulum high up on the inner
face, which, when the tooth is worn down to the proper level, unites
with the main part of the crown and incloses for a short time a small
pit. On the external face there is also a feeble cingulum near the base
of the enamel. The second incisor is greatly enlarged into a caniniform
tush. In the species _L. oxyrhynca_, this tooth is much smaller but
as this reduction of the tushes is the only difference, I consider
these forms as the female. The third incisor is again small, and has a
well-developed cingulum on both the front and inner faces. The canine
is similar to inc. 3.
The first premolar is much reduced in size, with a weak cingulum on
the outer face, and probably another on the inner side (the tooth is
too much worn in my specimen to be sure). Beginning with premolar
2, the upper teeth are molariform. The premolars are rectangular in
outline, each being much wider than long, and each having a cingulum
on the outer side. On the inner side, along the anterior half of each
premolar, there is a high cingulum, which, though interrupted at
the anterior corner, continues around onto the anterior face of the
tooth. On a worn tooth this anterior cingulum unites with the grinding
surface, and leaves a small pit in the anterior internal corner, which
is very suggestive of _Rhynchippidae_. In the middle of the grinding
surface, there is an oblique pit, the remains of the basin in young
teeth. The molars continue to increase in size toward the rear. They
have a vestige of a cingulum on the external side, no cingulum on the
inner side, but on the anterior side for about one third the distance
there is a cingulum similar to that on the premolars. In the middle of
the grinding surface is an elongated oblique pit, similar to that in
the premolars, but a little more advanced, there being a trace of the
development of cristae.
In the lower dentition, the first two incisors are small cropping
teeth, with the anterior face flattened and having a trace of a
cingulum; while on the inner face the cingulum is well developed.
Incisor 3 is developed into a tush corresponding to inc. 2 in the upper
dentition. As in the upper teeth, there are two types, that of _L.
oxyrhynca_ with the tush only about twice the size of an incisor, and
that of _L. gaudryi_ with it much larger.
All the premolars are molariform and of the typical toxodont character,
consisting of two crescents with a pillar and septum in the posterior
crescent. The septum, however, does not appear until on pm. 3 and on
all succeeding teeth, and is usually indicated by a tiny pit. From the
front to the back, the premolars are progressively larger, each having
a cingulum on both the internal and external faces. The molars continue
to increase in size progressively, and have the same characters as
the premolars, except that the crescents are more elongated, and the
cingula are gradually becoming smaller toward the rear.
The skull is low and heavy, with a low sagittal crest, and with the
lambdoidal crests continuous with the upper margin of the zygomatic
arches. The nasal bones are short and wide, and are markedly raised
above the nasal chamber. On the outer margin of each is a low boss,
somewhat as on the nasals of the rhinoceros, _Diceratherium_, which
would indicate that this form had a small pair of nasal horns.[15]
[Footnote 15: Scott has restored the head of _Leontinia gaudryi_ with
a single median horn, but no specimen in my collection would indicate
anything but a pair of nasal horns. See Scott, Mammals of the Western
Hemisphere, fig. 138, 1912.]
The frontal bones are broad, projecting laterally in strong postorbital
processes, which, with those from the jugals, almost close the orbit
behind. The premaxillae are peculiar in having a median crest on the
upper surface, the top of the crest being rugose, as though in life
it had continued upward as a cartilage septum. The maxillae rise well
up on the sides of the skull, bounding the lower part of the orbit,
and having a short zygomatic process. The small lachrymal is but
little exposed on the exterior surface of the skull, the lachrymal
pit being well inside the orbit. The zygomatic arches are broad and
heavy, and composed mostly of the wide jugal bones. The palate is
highly arched and relatively narrow, the crowns of the premolars and
molars projecting inward over it, thus narrowing it still more. It
extends back well beyond the last molar. The large tympanic bullae are
hollow, and the cavity in the squamosum seems to be reduced in size, as
compared with _Rhynchippidae_ or _Nesodontidae_. The occipital condyles
are set well apart and are sessile; and the paroccipital processes are
long and slender.
The atlas, axis and cervical 3 are associated with the skulls. The
atlas is short, heavy, and has the anterior cotyles broad, deeply
excavated and wide apart; while the posterior cotyles are nearly flat,
and high as well as wide. The transverse processes are only moderately
wide, but are very heavy, especially along the posterior margin. The
centrum of the axis is flattened, the neural canal, wider than high,
and the neural spine of moderate height. The anterior cotyles are broad
and moderately convex, and the odontoid process is a stout peg-like
process, somewhat higher than wide. Slender transverse processes
project sharply from the centrum, and have at their bases a large canal
for the vertebral artery. Cervical 3 is shorter than the axis, has a
less depressed centrum, a small neural spine, and short wide transverse
processes.
Though I have skulls and jaws to represent some twenty-five
individuals, no limb material was found in direct association with
any of them. However we did find a humerus, radius and ulna on the
same level and about fifteen feet from one of the skulls, and as it
corresponds in size, and as humeri of this type are the most abundant
skeletal bones found (as is also the case with the skulls), I have
considered it proper to associate these fore limb bones with these
skulls. The humerus is a stout bone, of medium length, with a large
sessile, and but little rounded head. The external tuberosity is
wide, thick and projects a little above the head, while the internal
tuberosity is so small as to be almost negligible. The shaft is
flattened laterally at the upper end, but distally is compressed in the
antero-posterior direction. The supratrochlear fossa is shallow, the
anconeal deep, but there is no foramen connecting them. The external
condyle is small, the internal much larger. The trochlea is narrow,
with a swollen articular area for the radius, and a wider saddle-like
one for the ulna. The ulna is a stout, nearly straight bone, slightly
longer than the humerus. The olecranon process, though large, is not
excessive. The sigmoid notch makes a deep semicircular cavity, with the
articular facets expanding on either side. It was closely fitted to
the radius so as to allow little or no rotary motion of the forearm.
The facet for the radius is a narrow band-like area just below the
sigmoid notch. The shaft is almost rectangular in section. Distally
the ulna contracts sharply into a heavy styloid process, on the end of
which is a large convex facet for the pyramidal, which merges without
interruption into the facet for the pisiform. The radius is a slenderer
bone, with a relatively small proximal head, but distally expanded into
a much larger articular end. My specimen is considerably weathered, but
shows a wide shallow articular facet for the humerus, and a band-like
facet for the ulna, but otherwise it gives little more than the length.
Of the hind limb, Gaudry[16] figures the astragulus and the calcaneum,
the former short and with a low trochlea, the latter also short and
with a broad facet for the fibula. Gaudry also states that the foot was
tridactyl and plantigrade, but I am doubtful of the plantigrade feature.
[Footnote 16: Annales Palaeontologie, 1906, t. 1, p. 28.]
Ameghino has made six species of this genus, _L. gaudryi_, _L.
fissicola_, _L. lapidosa_, _L. oxyrhynca_, _L. stenognatha_, and _L.
garzoni_. All of the first five are described as of the same size as
_L. gaudryi_. _L. garzoni_ is a smaller, about 60 per cent. of the
size of the others. Of the first five listed, the first three have the
large incisor and I consider them all _L. gaudryi_. _L. oxyrhynca_ and
_L. stenognatha_ are described as having small canines and I believe
that this is a sexual difference only, so have considered these two
species as also belonging to _L. gaudryi_, but females. I have made a
careful comparison of _L. gaudryi_ and _L. oxyrhynca_ and find them
identical in all the features except in the region of the canines where
the latter is weaker, and can see no more than sexual differences.
Usually with this weakness of the canine goes a smaller or lighter
build of the lower jaw which is what would be expected. The points by
which the various species were differentiated were, beside the size
of the canine, the presence or absence of pit 3, and the variation in
the foldings on the outer sides of the lower molars, which I find on
sectioning a tooth appear deeper or shallower according to whether the
tooth was more or less worn.
=Leontinia gaudryi= Ameghino
L. gaudryi Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 648.
L. gaudryi Amegh., 1897, Bol. Geog. Argen., t. 18, p. 472.
Scaphops grypus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 629.
Scaphops grypus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 475.
Steniogenium sclerops Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p.
654.
Steniogenium sclerops Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p.
475.
Leontinia fissicola Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p.
474.
L. (Senodon) lapidosa Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p.
649.
Females
L. oxyrhynca Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 472.
L. stenognatha Amegh., 1897, Bol. Inst. Geog. Argen., t. 15, p. 474.
Colpodon gaudryi Gaudry, 1906, Anal. Palaeontologie, t. 1, p. 30.
[Illustration: Fig. 69. Right upper dentition—½ natural size.]
[Illustration: Fig. 70. Lower dentition of male—½ natural size.]
[Illustration: Fig. 71. Lower dentition of female—½ natural size.]
This species is represented in the Amherst Collection by five more or
less complete skulls, and over twenty jaws, being by far the commonest
fossil of the Deseado beds on the Chico del Chubut River, west of
Puerto Visser. As mentioned above, there are two types, the first, with
larger canines and heavier mandibles, designated by Ameghino as _L.
gaudryi_, which I consider males; second, those with smaller canines,
and lighter mandibles, slightly smaller in size, which Ameghino
designated _L. oxyrhynca_ and I consider females. Practically all of
the other species are based on mandibular symphyses varying in details
from the above, but in no case sufficiently for me to see a specific
variation.
The general features have been discussed under the generic description.
Incisor 1 has a long crown and a long root, and is greatly crowded by
the tushes. Incisor 3 and pm. 1 have the same crowded appearance. In
giving the measurements I have used a skull which is typically _L.
gaudryi_, a male, and parallel to it have put another skull, which is
typically _L. oxyrhynca_, the female. By comparing the two sets of
figures, the shortening, of which Ameghino speaks, will be seen to be
all in the region of the tushes.
SPECIMEN SPECIMEN
3290 3291X
MALE FEMALE
Upper dentition, length from inc. 1 to m. 3 227 mm.
Upper dentition, length from pm. 1 to m. 3 180 mm.
Incisor 1, length 12 mm.
Incisor 2, length 25 mm.
Incisor 3, length 11 mm.
Canine, length 12 mm.
Premolar 1, length 12 mm.
Premolar 1, width 18 mm.
Premolar 2, length 18 mm.
Premolar 2, width 28 mm.
Premolar 3, length 20 mm.
Premolar 3, width 34 mm.
Premolar 4, length 22 mm. 20 mm.
Premolar 4, width 38 mm. 34 mm.
Molar 1, length 28 mm. 24 mm.
Molar 1, width 40 mm. 38 mm.
Molar 2, length 36 mm. 33 mm.
Molar 2, width 48 mm. 45 mm.
Molar 3, length 46 mm. 46 mm.
Molar 3, width 48 mm. 47 mm.
Lower dentition, height of mandible under m. 1 66 mm. 56 mm.
Incisor 1, length 8 mm. 8 mm.
Incisor 2, length 10 mm. 10 mm.
Incisor 3, length 23 mm. 13 mm.
Canine, length 8 mm. 9 mm.
Premolar 1, length 13 mm. 8 mm.
Premolar 1, width 12 mm. 12 mm.
Premolar 2, length 18 mm. 16 mm.
Premolar 2, width 17 mm. 15 mm.
Premolar 3, length 21 mm. 18 mm.
Premolar 3, width 19 mm. 16 mm.
Premolar 4, length 24 mm. 21 mm.
Premolar 4, width 19 mm. 18 mm.
Molar 1, length 33 mm. 27 mm.
Molar 1, width 20 mm. 20 mm.
Molar 2, length 40 mm. 37 mm.
Molar 2, width 20 mm. 20 mm.
Molar 3, length 57 mm. 57 mm.
Molar 3, width 20 mm. 20 mm.
[Illustration: Fig. 72. Top view of skull of L. gaudryi (female)—¼
natural size.]
In the skulls there is considerable variation in size in the different
individuals, but the proportions remain very much the same throughout.
In the female the snout is relatively a little shorter, and in general
the female skulls are from 5 to 10 per cent. smaller throughout. The
following two sets of figures illustrate the comparative sizes of the
two sexes.
[Illustration: Fig. 73. L. gaudryi, view of case of the skull, female
(L. oxyhynea)—¼ natural size; Tympanic bullae broken open.]
SPECIMEN SPECIMEN
3335 3291X
MALE FEMALE
Skull, greatest length front to back 420 mm. 392 mm.
Skull, greatest width 252 mm. 236 mm.
Skull, length of nasal bone 115 mm. 102 mm.
Skull, length of palate 235 mm. 230 mm.
The atlas associated with skull No. 3335 is a decidedly heavy bone in
all its proportions. The axis and the third cervical were associated
with skull No. 3291x, and are likewise heavy bones. The following are
typical measurements:
Atlas, greatest length 86 mm.
Atlas, greatest width 170 mm.
Axis, length of centrum and odontoid process 132 mm.
Axis, length of odontoid process 34 mm.
Axis, width across anterior cotyles 98 mm.
Cervical 3, length of centrum 66 mm.
Cervical 3, width of posterior end of centrum 55 mm.
[Illustration: Fig. 74. Atlas seen from below—¼ natural size.]
[Illustration: Fig. 75. Axis and cervical vertebra, No. 3—¼ natural
size.]
While there are other vertebrae in the collection, which probably
belong to this species, I have not cared to make the association
without some evidence of a definite character. However, in the case
of a fore limb, which was found fairly near one of the skulls, is of
proper size, and because this humerus occurs with something like the
frequency of the skulls, I have been convinced that it belonged to this
species, and so described it under the genus. This specimen consists of
the two humeri, the radius and the ulna, No. 3328.
Humerus, greatest length 314 mm.
Humerus, diameter of head 77 mm.
Humerus, transverse diameter of the shaft 43 mm.
Humerus, width of distal end 116 mm.
The ulna lacks some 60 mm. in the middle of the shaft, but when fitted
to the radius its length can readily be obtained. The radius is
considerably weathered so that measurements of the distal end are only
approximate.
Ulna, length over all 430 mm.
Ulna, transverse diameter of distal end 58 mm.
Radius, length over all 310 mm.
[Illustration: Fig. 76. Right humerus from the posterior side—¼ natural
size.]
[Illustration: Fig. 77. Right ulna from external side—¼ natural size.]
[Illustration: Fig. 78. Proximal end of right radius—¼ natural size.]
=Leontinia garzoni= Ameghino
L. garzoni, Amegh., 1896, Bol. Inst. Geog. Argen., t. 15, p. 650.
L. garzoni, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 474.
We were not fortunate enough to find this species, but as described by
Ameghino it is about 60 per cent. of the size of _L. gaudryi_. The type
is a lower jaw, for which the following figures are given:
Lower dentition, length from pm. 1 to m. 3 120 mm.
Lower dentition, length from pm. 1 to pm. 4 45 mm.
Lower dentition, length of pm. 4 15 mm.
Lower dentition, length of m. 3 39 mm.
=Ancylocoelus= Ameghino
Ancylocoelus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 652.
Ancylocoelus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 475.
Rodiotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 653.
Rodiotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 476.
This genus differs from _Leontinia_ in its formula,
3 0 4 3
-------
3 0 3 3
but, except for the loss of these canines and the lower premolars, is
very similar. In this it seems to approach the line which gave rise to
_Colopdon_. The premolars and molars are also narrower in proportion
than in _Leontinia_. I have placed _Rodiotherium_ also under this genus
as I can not see a generic difference in the descriptions. However we
were not fortunate enough to find these forms. Ameghino has described
four species as follows:
=A. frequens=, 1895, Bol. Inst. Geog. Argen., t. 15, p. 475.
Upper dentition, pm. 1 to m. 3 150 mm.
Lower dentition, pm. 2 to m. 3 150 mm.
Upper molar 3, length 39 mm.
=A. lentus=, 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 407.
Upper molar 3, length 48 mm.
=A. minor=, 1901, loc. cit.
Upper molar 3 34 mm.
=A. (Rodiotherium) armatum=, see cit. above.
Based on an imperfect mandibular symphysis, in which incisor 3 is very
large.