Odd-toed ungulate (Perissodactyla)
Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (from Ancient Greek περισσός, perissós 'odd', and δάκτυλος, dáktylos 'finger, toe'), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using 4 toes on the front legs) or even one (horses, third toe) of the five original toes. The non-weight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, the even-toed ungulates bear most of their weight equally on 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.
The order includes about 17 species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs).
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 name.