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Odd-toed ungulate

The meaning of «odd-toed ungulate»

Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (/pəˌrɪsoʊˈdæktɪlə/, 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 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.

The largest odd-toed ungulates are rhinoceroses, and the extinct Paraceratherium, a hornless rhino from the Oligocene, is considered one of the largest land mammals of all time.[2] At the other extreme, an early member of the order, the prehistoric horse Eohippus, had a withers height of only 30 to 60 cm (12 to 24 in).[3] Apart from dwarf varieties of the domestic horse and donkey, perissodactyls reach a body length of 180–420 cm (71–165 in) and a weight of 150 to 4,500 kg (330 to 9,920 lb).[4] While rhinos have only sparse hair and exhibit a thick epidermis, tapirs and horses have dense, short coats. Most species are grey or brown, although zebras and young tapirs are striped.

The main axes of both the front and rear feet pass through the third toe, which is always the largest. The remaining toes have been reduced in size to varying degrees. Tapirs, which are adapted to walking on soft ground, have four toes on their fore feet and three on their hind feet. Living rhinos have three toes on both the front and hind feet. Modern equines possess only a single toe; however, their feet are equipped with hooves, which almost completely cover the toe. Rhinos and tapirs, by contrast, have hooves covering only the leading edge of the toes, with the bottom being soft.

Ungulates have stances that require them to stand on the tips of their toes. Equine ungulates with only one digit or hoof have decreased mobility in their limb allows for faster running speeds and agility. Differences in limb structure and physiology between ungulates and other mammals can be seen in the shape of the humerus. For example, often shorter, thicker, bones belong to the largest and heaviest ungulates like the Rhinoceros.[5]

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