I. †Meniscotheriidæ.
†Meniscotherium, Wasatch and Wind River.
II. †Phenacodontidæ.
†Protogonodon, Puerco. †Euprotogonia, Torrejon. †Phenacodus, Wasatch and Wind River.
1. †Phenacodontidæ
The typical Wasatch genus †Phenacodus, which is very fully known from nearly complete skeletons, included species which varied in size from a fox to a small sheep; the same genus occurred in the Wind River, but not later. †Phenacodus had the unreduced dental formula: i 3/3, c 1/1, p 4/4, m 3/3, × 2 = 44.
Fig. 233.—Skeleton of the Wasatch †condylarth, †Phenacodus primævus. American Museum. For restoration, see [Fig. 141, p. 278].
The incisors were small and simple, the canines tusk-like, but of no very great size, the premolars smaller and simpler than the molars. The latter were of the quadrituberculate pattern, of four simple, conical cusps arranged in two pairs, a pattern which is common to the earlier and less specialized members of many ungulate groups. The skull was long, narrow and low, with long and well-defined sagittal crest. As in primitive skulls generally, the cranial region was long and the face short, the eyes being very far forward; this does not imply large brain-capacity, indeed, the brain was very small, but merely that the portion of the skull behind the eyes was relatively long. The jaws were short and shallow, in accordance with the small and low-crowned teeth which they carried. The neck was of medium length, but the body was elongate and the tail was very long and stout. The hip-bones were narrow and slender, as in primitive ungulates generally. The limbs were short and stout and retained many very primitive characteristics. The humerus had a prominent deltoid crest and an epicondylar foramen; the fore-arm bones were separate and the ulna quite unreduced, being almost as stout as the radius. The femur had the third trochanter and the leg-bones were distinct, though the fibula was slender. The feet, which were short, had five digits each, but the third toe was enlarged, while the first and fifth were shortened, as though preparing to disappear and thus give rise to a three-toed perissodactyl foot. The ankle-bone (astragalus) had a rounded, convex lower end, fitting into the navicular, so that it might readily be taken for that of a clawed mammal.