Odd-toed Ungulate - Characteristics

Characteristics

The living perissodactyls are a diverse group. At one extreme are the lithe and graceful horses; on another, the huge, tank-like rhinoceroses; and in the middle, the vaguely pig-like tapirs. All extant perissodactyls are large, from the 180-kg mountain tapir to the 2,300-kg white rhinoceros.

Extinct perissodactyls possessed a far more diverse range of forms, including the tiny, vaguely tapir-like paleotheres, the monstrous brontotheres, the knuckle-walking chalicotheres, and the gigantic rhinoceros Indricotherium, which dwarfed even elephants.

However, all perissodactyls, extinct and extant, have a mesaxonic foot structure. In other words, the symmetry of the foot passes through the third digit, which holds the animal's weight. In equines, the mesaxonic foot has been modified so the nonweight bearing digits have atrophied away, while the third toe has enlarged, so modern equines only have one toe. Also, all perissodactyls are hindgut fermenters. Hindgut fermenters, in contrast to the ruminants, store digested food which has left the stomach in a pouch-like extension of the large intestine called the cecum (literally "cave"), where the food is digested by bacteria. No gallbladder is present.