The horses (_†Orohippus_) were very small and primitive creatures, no bigger than a fox, with four toes in the front foot and three in the hind. So completely different in appearance and proportions were these little animals from any of the modern horses, that it requires an effort of the imagination to think of them as belonging to the same family, and it is only by employing the family to designate a _genetic series_ that such a classification can be justified. The †hyracodonts, or cursorial rhinoceroses, were very abundantly represented by a number of small and medium-sized animals (_†Hyrachyus_) which had less specialized teeth, shorter neck and limbs than their upper Eocene and Oligocene successors, and four toes in the front foot; one genus (_†Colonoceras_) had a pair of nasal horns, but would seem to have died out without leaving descendants. In the upper part of the beds is found the Uinta genus _†Triplopus_, with three-toed fore foot; and in the same division occurs another Uinta genus, _†Amynodon_, the most ancient known species of the supposedly aquatic rhinoceroses. True rhinoceroses, that is animals which were directly ancestral to the modern members of the family, have not been identified and may not have been present in North America; that is still an open question. Tapirs, all of them quite small, were relatively common, but are still very incompletely known. The earliest known members of the clawed †chalicotheres were of Bridger date. It is worth remarking that, except a single genus in the upper and later portion of the stage (_†Triplopus_), all of the Bridger perissodactyls had four toes in the front foot and three in the hind, while in the White River beds above the lowest substage the number three in both fore and hind feet was almost equally universal. One of the most radical and striking differences between the Uinta and Bridger faunas was the rarity of Artiodactyla in the latter, which is in almost equally strong contrast with their abundance in the middle Eocene of Europe. Most significant of these rare Bridger artiodactyls were the little creatures (_†Homacodon_), hardly so large as a domestic cat, which may fairly be regarded as a very early stage, if not the actual beginning, of the great camel family, which was destined to play so conspicuous a part in the life of America, North and South. Small pig-like animals (_†Helohyus_) which were no doubt ancestral to the peccaries, were fairly common and there were, in addition, relatively large animals (_†Achænodon_) allied, but not ancestral, to the †giant-pigs of the Oligocene; some of these were considerably larger than a full-grown Wild Boar (_Sus scrofa_).