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Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (from the Ancient Greek περισσός perissós, "uneven"; and δάκτυλος dáktylos, "finger, toe"), are hoofed animalsungulates—which bear most of their weight on one (an odd number) of the five toes: the third toe. 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 the even-toed ungulates 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.

Phylogenetic tree


  Isectolophidae (†)


  Lophiodontidae (†)


  Chalicotheriidae (†)


  Helaletidae (†)




  Amynodontidae (†)


  Hyracodontidae (†)




  Palaeotheriidae (†)




  Lambdotheriidae (†)


  Brontotheriidae (†)


Cladogram below is for existing Perissodactyla


  Equus ferus


  Equus asinus


  Equus kiang


  Equus hemionus


  Equus zebra


  Equus quagga


  Equus grevyi


  Tapirus indicus


  Tapirus bairdii


  Tapirus kabomani


  Tapirus pinchaque


  Tapirus terrestris


  Rhinoceros unicornis


  Rhinoceros sondaicus


  Dicerorhinus sumatrensis


  Ceratotherium simum


  Diceros bicornis



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