The whole Eocene of North America had a series of pig-like animals, called the †achænodonts or †short-faced pigs, which seem to have been related to the †entelodonts. They ended their career in the Uinta just before the appearance of the †entelodonts, and it would be natural to suppose that the latter were descended from them. If, however, the principle that an organ or structure once lost can never be regained, is valid, then there can be no relation of ancestor and descendant between the two groups, for of the †achænodonts, even their most ancient representatives had lost the first premolar, giving the formula p 3/3, while in the †entelodonts it is constantly p 4/4. The †achænodonts, which are much less fully known than the †entelodonts, had teeth very similar in form to those of the latter; and their most conspicuous feature was the shortness of the face and jaws, as contrasted with the extreme elongation of these parts in the †entelodonts, nor did they have the bony flaps under the eyes or the knobs on the lower jaw which gave such a fantastic appearance to the †entelodont skull. Little is known of the skeleton except that there were four functional digits in the manus. The Uinta and Bridger genus (†Achænodon) was larger than the Wasatch form (†Parahyus), which was an immigrant, probably from the same region as afterwards sent out the †entelodonts to America and Europe; this would account for the similarity and probable relationship of the two subfamilies.

Suborder Artiodactyla †Primitiva. †Primitive Artiodactyls

No doubt, this suborder is an artificial assemblage of unrelated families, a sort of waste-basket, into which are thrown the groups of which no other disposition can be made in the present state of knowledge. As information becomes more complete, the various families will be redistributed among the groups with which they had a genuine relationship.

3. †Anthracotheriidæ. †Anthracotheres

This family was abundantly represented in Europe from the middle Eocene through the Oligocene, in Asia persisting even into the Pliocene, and were abundant in the Oligocene of Egypt. Migrants from the Old World reached America in White River times, but speedily died out, as they did not survive into the upper Oligocene. The most fully known of these animals is an American species of a European genus †Bothriodon. Almost complete skeletons of this genus have been obtained in the channel sandstones of the upper White River substage. In size and proportions, †Bothriodon was not unlike a domestic pig, but had a very long head with slender, pointed snout; it had also a short neck, long body, short limbs and feet. The primitive character of this genus is made clear by many features of its structure; the molar teeth were extremely low-crowned and their cusps were so imperfectly crescentic in form as to be called buno-selenodont, as indicating their transitional nature, and the upper molars had five cusps instead of four, a very primitive feature. Another very significant character was the five-toed manus; the first digit, or pollex, was much smaller than the others.

Fig. 196.—†Bothriodon brachyrhynchus, upper White River stage. Restored from a skeleton in the museum of Princeton University.

The second genus of the family which had American representatives was †Anthracotherium, which was much like †Bothriodon, but even more archaic in character; the molars could hardly be called selenodont at all.

4. †Oreodontidæ. †Oreodonts