Temporal range: 35–0Ma Early Oligocene to Recent
|Linnaeus's two-toed sloth (Choloepus didactylus)|
Choloepus is a genus of mammals of Central and South America, within the family Megalonychidae consisting of two-toed sloths. There are only two species of Choloepus (which name means "lame foot"): Linnaeus's two-toed sloth (Choloepus didactylus) and Hoffmann's two-toed sloth (Choloepus hoffmanni). These two species are the only surviving 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. Recent phylogenetic analyses support analysis of morphological data from the 1970s and 1980s, suggesting that the two genera are not closely related and that each adopted their arboreal lifestyles independently. It is unclear what, if any, ground-dwelling sloth taxa the three-toed sloths evolved from; the two-toed sloths appear to nest phylogenetically within one of the divisions of Caribbean megalonychids, and thus probably either descended from them or are part of a clade that invaded the Caribbean multiple times. 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.
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.
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 upside down from trees. They cannot walk so they pull hand over hand to move around, which is at an extremely slow rate. Being predominately nocturnal, their fur, which grows a greenish algae to blend in, is their main source of protection. 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. Two-toed sloths also differ from three-toed in their climbing behaviors, preferring to descend head first.
They eat primarily leaves, but also shoots, fruits, nuts, berries, bark, some native flowers, and even some small rodents. In addition, when they cannot find food they have been known to eat the algae that grows on their fur for nutrients. 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. 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). They have a reduced, ever growing dentition, with no incisors or true canines, and which overall lacks homology with the dental formula of other mammals. Their first tooth is very canine-like in shape and is referred to as a caniniform. It is separated from the other teeth, or molariforms, by a diastema. The molariforms are used specifically for grinding and are mortar and pestel-like in appearance and function. Thus, they can grind food for easier digestability, which takes majority of their energy. The dental formula of two-toed sloths is:4 (unau)
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- 30% body weight
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- National Geographic: Two-toed sloth profile
- Bristol Zoo: Two-toed sloth
- National Zoo: Two-toed sloth
- America Zoo: Two-toed sloth
- Animal Diversity: Family Megalonychidae