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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

 Perissodactyla 
 Tapiromorpha 
 

  Isectolophidae (†)

 
 
 Ancylopoda 
 

  Lophiodontidae (†)

 
 

  Chalicotheriidae (†)

 
 
 Ceratomorpha 
 Tapiroidea 
 

  Helaletidae (†)

 
 

  Tapiridae

 
 
 Rhinocerotoidea 
 

  Amynodontidae (†)

 
 
 

  Hyracodontidae (†)

 
 

  Rhinocerotidae

 
 
 
 
 
 
 Hippomorpha 
 Equoidea 
 

  Palaeotheriidae (†)

 
 

  Equidae

 
 
 Brontotherioidea 
 

  Lambdotheriidae (†)

 
 

  Brontotheriidae (†)

 
 
 
 


Cladogram below is for existing Perissodactyla

 Perissodactyla 
 
 Equidae
 

  Equus ferus

 
 
 

  Equus asinus

 
 
 
 

  Equus kiang

 
 

  Equus hemionus

 
 
 
 

  Equus zebra

 
 
 

  Equus quagga

 
 

  Equus grevyi

 
 
 
 
 
 
 
 Tapiridae
 

  Tapirus indicus

 
 
 

  Tapirus bairdii

 
 
 

  Tapirus kabomani

 
 
 

  Tapirus pinchaque

 
 

  Tapirus terrestris

 
 
 
 
 
 Rhinocerotidae
 
 
 

  Rhinoceros unicornis

 
 

  Rhinoceros sondaicus

 
 
 

  Dicerorhinus sumatrensis

 
 
 
 

  Ceratotherium simum

 
 

  Diceros bicornis

 
 
 
 
 
 

References

This page uses content that though originally imported from the Wikipedia article Odd-toed ungulate might have been very heavily modified, perhaps even to the point of disagreeing completely with the original wikipedia article.
The list of authors can be seen in the page history. The text of Wikipedia is available under the Creative Commons Licence.
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