What are Odd-Toed Ungulates?

Michael Anissimov
Michael Anissimov

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.

Zebras are odd-toed ungulates.
Zebras are odd-toed ungulates.

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.

Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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