Perissodactyla is an order of placental mammals composed of odd-toed ungulates – hooved animals which bear weight on one or three of their five toes with the other toes either present, absent, vestigial, or pointing backwards. Members of this order are called perissodactyls, and include rhinoceroses, tapirs, and horses. They are primarily found in Africa, southern and southeastern Asia, and Central America, and are found in a variety of biomes, most typically grassland, savanna, inland wetlands, shrubland, and desert. Perissodactyls range in size from the 1.8 m (6 ft) long Baird's tapir to the 4 m (13 ft) long white rhinoceros. Over 50 million domesticated donkeys and 58 million horses are used in farming worldwide, while four species of perissodactyl have potentially fewer than 200 members remaining. Three subspecies of the black rhinoceros, the Syrian wild ass subspecies of the onager, and the tarpan subspecies of the wild horse have gone extinct in the last 200 years.
The eighteen extant species of Perissodactyla are divided into two suborders: Ceratomorpha, containing the families Rhinocerotidae and Tapiridae, and Hippomorpha, containing the family Equidae. Rhinocerotidae contains five species of rhinoceroses split into four genera, Tapiridae contains four species of tapir in a single genus, and Equidae contains nine species in a single genus, including horses, donkeys, and zebras. Over 75 extinct Perissodactyla species have been discovered, though due to ongoing research and discoveries the exact number and categorization is not fixed.[1]