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

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]

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.

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

Fig. 69. Right
upper
dentition—
½ natural size.

Fig. 70. Lower
dentition
of male—
½ natural size.

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
3290
Male		Specimen
3291x
Female
Upper dentition,length from inc. 1 to m. 3227 mm.
Upper dentition,length from pm. 1 to m. 3180 mm.
Incisor 1,length12 mm.
Incisor 2,length25 mm.
Incisor 3,length11 mm.
Canine,length12 mm.
Premolar 1,length12 mm.
Premolar 1,width18 mm.
Premolar 2,length18 mm.
Premolar 2,width28 mm.
Premolar 3,length20 mm.
Premolar 3,width34 mm.
Premolar 4,length22 mm.20 mm.
Premolar 4,width38 mm.34 mm.
Molar 1,length28 mm.24 mm.
Molar 1,width40 mm.38 mm.
Molar 2,length36 mm.33 mm.
Molar 2,width48 mm.45 mm.
Molar 3,length46 mm.46 mm.
Molar 3,width48 mm.47 mm.
Lower dentition,height of mandible under m. 166 mm.56 mm.
Incisor 1,length8 mm.8 mm.
Incisor 2,length10 mm.10 mm.
Incisor 3,length23 mm.13 mm.
Canine,length8 mm.9 mm.
Premolar 1,length13 mm.8 mm.
Premolar 1,width12 mm.12 mm.
Premolar 2,length18 mm.16 mm.
Premolar 2,width17 mm.15 mm.
Premolar 3,length21 mm.18 mm.
Premolar 3,width19 mm.16 mm.
Premolar 4,length24 mm.21 mm.
Premolar 4,width19 mm.18 mm.
Molar 1,length33 mm.27 mm.
Molar 1,width20 mm.20 mm.
Molar 2,length40 mm.37 mm.
Molar 2,width20 mm.20 mm.
Molar 3,length57 mm.57 mm.
Molar 3,width20 mm.20 mm.

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.

Fig. 73. L. gaudryi, view of case of the skull,
female (L. oxyhynea)—¼ natural size;
Tympanic bullae broken open.

Specimen
3335
Male		 Specimen
3291x
Female
Skull,greatest length front to back 420 mm.392 mm.
Skull,greatest width252 mm.236 mm.
Skull,length of nasal bone115 mm.102 mm.
Skull,length of palate235 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 length86 mm.
Atlas,greatest width170 mm.
Axis,length of centrum and odontoid process 132 mm.
Axis,length of odontoid process34 mm.
Axis,width across anterior cotyles98 mm.
Cervical 3,length of centrum66 mm.
Cervical 3,width of posterior end of centrum55 mm.

Fig. 74. Atlas seen
from below—
¼ natural size.

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 length314 mm.
Humerus,diameter of head77 mm.
Humerus,transverse diameter of the shaft  43 mm.
Humerus,width of distal end116 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 all430 mm.
Ulna,transverse diameter of distal end  58 mm.
Radius,length over all310 mm.

Fig. 76. Right humerus
from the posterior
side—¼ natural size.

Fig. 77. Right ulna
from external
side—¼ natural size.

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. 3120 mm.
Lower dentition,length from pm. 1 to pm. 445 mm.
Lower dentition,length of pm. 415 mm.
Lower dentition,length of m. 339 mm.