What are Odd-Toed Ungulates?

Odd-toed ungulates consist of ungulates (hoofed animals) with an odd number of weight-bearing toes, either one or three. Odd-toed ungulates make up a mammalian order, Perissodactyla. Members include tapirs, rhinos, horses, zebras, and asses. Odd-toed ungulates are not nearly as important economically as even-toed ungulates like pigs and cattle, but they are admired by nature-lovers and equestrians. They have a worldwide range, from the South/Central American tapir to the African Zebra. Odd-toed ungulates are hindgut fermenters, meaning that they digest cellulose in their intestines rather than stomach.

Unlike their cousins, the even-toed ungulates, odd-toed ungulates have relatively simple one-chambered stomachs. They are often generalized as unusually large, and the smallest odd-toed ungulate (the tapir) has a weight larger than that of most men. The largest odd-toed ungulate is the White Rhinoceros, which is as long as 4.2 m (13.75 ft), about 1.85 m (6 ft) tall, and weighs as much as 4,500 kg (10,000 lbs), or four and a half tonnes. The White Rhinoceros is the largest land animal in the world after the elephants.

Like most other mammalian orders, odd-toed ungulates first evolved in the Early Eocene, about 50 million years ago, not long after the extinction of the dinosaurs. Very quickly, the odd-toed ungulates spread out across all the world's continents. Horses and tapirs originated in North America, while rhinos evolved in Eurasia from tapir-like ancestors and went on to colonize the entire world. Though there have historically been 15 families of rhinoceros, only 3 live today, and many of the species are endangered.

One of the most famous odd-toed ungulates is the extinct Indricotherium, also known as Paraceratherium, a huge rhinoceros-like animal with a long neck that is the largest land animal that ever lived. Dwarfing today's elephants, Indricotherium was about 5.5 m (18 ft) tall at the shoulder, over 8 m (26 ft) in length (without the tail), with a head height of no more than 7.5 m (25 ft), and a skull length of 1.35 m (4.5 ft). Grazing tall trees in Eurasia between about 30 and 20 million years ago, Indricotherium is often compared to a small sauropod because of its dimensions.