Although palaeotheres resemble tapirs in general appearance, they differ in having only three toes on the fore as well as on the hind foot.
In the tapirs and many extinct forms the fifth toe also remains on the fore-limb, but its presence does not interfere with the symmetrical arrangement of the remainder of the foot on each side of the median line of the third or middle digit.
The Perissodactyla may be divided into the four following sections, namely the extinct Titanotheroidea, the Hippoidea, represented by the horse tribe and their ancestors, the Tapiroidea, typified by the tapirs, and the Rhinocerotoidea, which includes the modern rhinoceroses and their forerunners.
In North America the earliest representative of the group is Systemodon of the Lower Eocene, in which all the upper premolars are quite simple; while the molars are of a type which would readily develop into that of the modern tapirs, both outer columns being conical and of equal size.
In Anoplotherium, some of the species of which were larger than tapirs, there were either two or three toes, the latter number being almost unique among the Artiodactyla.