What order of mammals includes horses, rhinoceroses, and tapirs?

The order of mammals that includes horses, rhinoceroses, and tapirs is Perissodactyla.

Perissodactyla means “odd-toed” ungulates. Living members belong to three families: Equidae, which includes horses, asses, and zebras; Rhinocerotidae, the rhinoceroses; and Tapiridae, the tapirs. Their ancestors and extinct relatives were far more diverse than the modern group.

The name refers to foot structure. Most living perissodactyls carry their weight on one or three toes, unlike even-toed artiodactyls such as cattle, deer, pigs, and camels. Tapirs are a useful exception to simplistic hoof comparisons because they retain four toes on each forefoot and three on each hind foot.

A common mix-up is confusing this order with Artiodactyla. Both are hoofed mammal groups, but horses, rhinos, and tapirs are the classic odd-toed trio. Richard Owen introduced the name Perissodactyla in the nineteenth century as scientists worked to classify hoofed mammals by their anatomy.