Perissodactyla (cohort Ferungulata, superorder Mesaxonia) An order that comprises those ungulates in which the number of functional toes is reduced to three or one, and a fourth, if present, is reduced, the weight of the animal being borne by the central digit. The order includes the three suborders Ceratomorpha (tapirs, rhinoceroses, and their extinct relatives), Ancylopoda (extinct forms), and Hippomorpha (horse-like forms). They appeared in the Eocene, derived from the Condylarthra, and reached their zenith in the mid-Tertiary, when they were the most numerous of ungulates. So many fossil remains of them have been found that their evolutionary history is known in greater detail than that of any other mammalian group. Since then the order has declined dramatically, having been displaced by the Artiodactyla, and the group as a whole is moving towards extinction.

Perissodactyla (cohort Ferungulata) Odd-toed ungulates. Order that comprises those ungulates in which the number of functional toes is reduced to three or one, and a fourth, if present, is reduced, the weight of the animal being borne by the central digit. The order includes the three suborders Ceratomorpha (tapirs, rhinoceroses, and their extinct relatives); Ancylopoda (or Chalicotheres), which are extinct forms with claw-like extremities in place of hoofs, e.g. Moropus; and Hippomorpha (horse-like forms). They appeared in the Eocene, derived from the condylarths, and reached their zenith in the mid-Tertiary, when they were the most numerous of ungulates. So many fossil remains of them have been found that their evolutionary history is known in greater detail than that of any other mammalian group. Since then the order has declined dramatically, having been displaced by the artiodactyls, and the group as a whole is moving towards extinction.

Perissodactyla An order of mammals having hoofed feet with an odd number of toes. They are all herbivores and include the tapirs, rhinoceros, and horse. The teeth are large and specialized for grinding. Cellulose digestion occurs in the caecum and large intestine. Fossils of the Eocene epoch, 60 million years ago, show that these animals were at that time already distinct from the cloven-hoofed Artiodactyla.