二趾樹懶屬
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 霍氏樹懶 C. hoffmanni
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二趾樹懶屬（學名：Choloepus），是樹懶亞目下二趾樹懶科中的唯一一屬，僅包括兩個物種。分別是二趾樹懶（C. hoffmanni）及霍氏樹懶（C. didactylus）。
The two extant species of two-toed sloths are Linnaeus's (Choloepus didactylus) and Hoffmann's Two-toed Sloth (Choloepus hoffmanni). They are the only members of the genus Choloepus, which name means "lame foot" and are the only living members of the family Megalonychidae. Although similar to the somewhat smaller and generally slower moving three-toed sloths (Bradypus), there is not a close relationship between the two genera. Both types tend to occupy the same forests: in most areas, a particular single species of three-toed sloth and a single species of the larger two-toed type will jointly predominate.
Characteristics
As the name implies, they have only two toes on their forefeet, although, like other sloths, they have three toes on the hindfeet. They are also larger than three-toed sloths, having a body length of between 58 and 70 centimetres, and weighing 4-8 kilograms. Other distinguishing features include a more prominent snout, longer fur, and the absence of a tail.[1]
Two-toed sloths have a gestation period of between six months and a year, depending on the exact species. The mother gives birth to a single young, while hanging up-side down. The young are born with claws, and are weaned after about a month, although they will remain with the mother for several more months, and do not reach sexual maturity until the age of 3 years, in the case of females, or 4-5 years, in the case of males.
Two-toed sloths spend most of their life hanging from trees, and are generally nocturnal animals. They are somewhat more active than three-toed sloths. Their body temperature depends at least partially on the ambient temperature; they cannot shiver to keep warm, as other mammals do, because of their unusually low metabolic rates and reduced musculature.[1] Two-toed sloths also differ from three-toed in their climbing behaviors, preferring to descend head first.
They eat fruits, nuts, berries, bark, and occasionally small rodents. They have large stomachs, with multiple chambers, which help to ferment the large amount of plant matter that they eat. Food can take up to a month to digest due to their slow metabolism.[1] Depending on when in the excretion cycle a sloth is weighed, urine and feces may account for up to 30 percent of the animal’s body weight, which averages about 6 kilograms (about 13 pounds).[2] They have a reduced dentition, with no incisors or true canines, although their first premolars do have a canine-like shape, and are separated from the other teeth by a diastema. The dental formula of two-toed sloths is:
| 0.0.1-2.3 |
| 0.0.1.3 |
- ^ 1.0 1.1 1.2 Dickman, Christopher R. Macdonald, D. , 编. The Encyclopedia of Mammals. New York: Facts on File. 1984: 776–779. ISBN 0-87196-871-1.
- ^ 30% body weight