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Perissodactyla
literally means "odd-toed." This order is
comprised of the horses, rhinos, and tapirs. The name
originates from the fact that most species have three
toes on the hindfoot and three or four on the forelimbs.
Some species only possess a single toe. The middle toe
is generally larger than its counterparts. About 60
million years ago, this dominant group was represented
by 14 scientific families. That diverse group of animals
has now been reduced to only 3 remaining families and
18 recognized species. Several members of this order
are highly endangered and face many environmental challenges.
Their overall decline appears to be related to the rise
of the even-toed ungulates. Modern species are native
to Africa, south and central Asia, southern North America,
and northern South America.
A
few species possess horns, but these are derived from
the epidermis. Perissodactyls differ from artiodactyls
in the fact that their horns are not supported by bone
tissue. Artiodactyls also possess paired horns. Perissodactyls
have a simple stomach, while their even-toed counterparts
tend to feature a chambered stomach. These animals have
up to 44 large cheek teeth that are specially designed
to process their highly herbivorous diet. An enlarged
cecum may contribute to the effective digestion of plant
material.
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