SUBORDER †TALIGRADA
None of the ungulate series considered in the foregoing chapters can be traced back to a time earlier than the Wasatch, and many of them not so far, but in the case of the †Amblypoda the line may be carried down through the Paleocene. In the upper stage of that epoch (Torrejon) the order was represented by †Pantolambda ([Fig. 143, p. 285]), a member of the third suborder, †Taligrada. The best-known species of the genus was an animal with head and body somewhat smaller than those of a sheep and much shorter legs. The teeth were present in unreduced number, 44 in all; the canines were tusk-like, but very much smaller proportionately than those of †Coryphodon; the premolars were smaller and simpler than the molars, which closely represent the common starting point, whence the curious tooth-patterns found in the subsequent genera of the various families were derived. The skull was long and narrow and had a prominent sagittal crest; the neck was of ordinary length, about equal to that of the head; the body was long and the tail very long, much as in the great cats. The hip-bones were narrow and slender and not bent outward, having no such breadth as in †Coryphodon. The limbs were short and relatively heavy, and the various bones were of such primitive character that, if found isolated and not in association with teeth or foot-bones, one would hardly venture to consider them as belonging to any hoofed animal; the humerus had a very prominent deltoid crest and an epicondylar foramen, and the femur had the third trochanter. The five-toed feet were very short, and the digits were arranged in a spreading manner and were relatively much more slender than in †Coryphodon. Each digit terminated in a flat, pointed, well-developed hoof; evidently there was no elastic pad to bear the weight, such as recurs in nearly all very heavy ungulates. The gait of the animal was probably semi-plantigrade, the hoofs being the principal points of support.
While †Pantolambda was an undoubted ungulate and a member of the †Amblypoda, there were many structural features in its skeleton which point to a relationship with the primitive flesh-eaters. In the lower stage of the Paleocene, the Puerco, the genus †Periptychus would seem to be the most ancient known member of the order, but it is still very imperfectly understood.
In the mode of evolution of the †Amblypoda, so far as that is recorded by the fossils, there is much to recall the development of the Proboscidea, though the story began and ended at far earlier dates and may be traced back to a much more primitive stage.
(1) There was a rapid increase of stature, especially of bulk, in the †coryphodonts, but decidedly more gradual in the †uintatheres, which eventually attained a far larger size.
(2) The upper incisors were suppressed and the canines grew into formidable tusks, at first straight, then the superior one, enlarging still farther, acquired a curved, scimitar-like shape, while the inferior one dwindled and became functionally one of the incisors.
(3) The grinding teeth remained low-crowned throughout, but acquired a more complex pattern, and the premolars became almost like the molars.
(4) The skull underwent a most remarkable transformation. Beginning with a form that might have belonged to almost any of the ancient mammals, hoofed or clawed, having very prominent sagittal and occipital crests, long cranium and short face, it became in †Coryphodon flat-roofed, with moderately elongated face, while in the †uintatheres the top of the cranium gradually took on a deeply concave basin-shape and, with equal gradualness, three pairs of horn-like protuberances; the lower jaw developed a great bony flange for the protection of the upper tusks. These peculiarities grew more and more exaggerated and were most striking in the terminal genus of the series, †Eobasileus.