Perissodactyla
Perissodactyla (/pəˌrɪsoʊˈdæktɪlə/, from Ancient Greek περισσός, perissós 'odd', and δάκτυλος, dáktylos 'finger, toe') is an order of ungulates. The order includes about 17 living species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They typically have reduced the weight-bearing toes to three or one of the five original toes, though tapirs retain four toes on their front feet. The nonweight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, artiodactyls (even-toed ungulates) bear most of their weight equally on four or two (an even number) of the five toes: their third and fourth toes. Another difference between the two is that odd-toed ungulates digest plant cellulose in their intestines, rather than in one or more stomach chambers as even-toed ungulates, with the exception of Suina, do.
| Perissodactyla Temporal range: Latest Paleocene–present | |
|---|---|
| Clockwise from left: plains zebra (Equus quagga), Indian rhinoceros (Rhinoceros unicornis) and Brazilian tapir (Tapirus terrestris) | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Clade: | Perissodactylamorpha |
| Order: | Perissodactyla Owen, 1848 |
| Families | |
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The order was considerably more diverse in the past, with notable extinct groups include the brontotheres, palaeotheres, chalicotheres, and the paraceratheres, with the paraceratheres including the largest known land mammals to have ever existed.
Despite their very different appearances, they were recognized as related families in the 19th century by the zoologist Richard Owen, who also coined the order's name.