Two-toed sloth

Two-toed sloths[1] Temporal range: 35–0 Ma PreЄ Є O S D C P T J K Pg N Early Oligocene to Recent
Linnaeus's Two-toed Sloth (Choloepus didactylus)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Superorder:	Xenarthra
Order:	Pilosa
Suborder:	Folivora
Family:	Megalonychidae
Genus:	Choloepus Linnaeus, 1758
Species
Choloepus didactylus Choloepus hoffmanni

Choloepus is a genus of mammals of Central and South America, within the family Megalonychidae consisting of two-toed sloths.^[2] There are only two species of Choloepus (which name means "lame foot"^[3]): Linnaeus's Two-toed Sloth (Choloepus didactylus) and Hoffmann's Two-toed Sloth (Choloepus hoffmanni). These two species are the only members of the family Megalonychidae.^[4]

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^[5] support the morphological data from the 1970s and 1980s 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,^[6] 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.

Characteristics

Display of two toes on front foot and three toes on rear foot.

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.^[7]

Young C. hoffmanni being raised in a wildlife rescue center in the Osa Peninsula, Costa Rica.

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.^{[citation needed]} 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.^[7] 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, and occasionally small rodents.^[4] 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.^[7] 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).^[8] 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 dental formula of two-toed sloths is:$Upper: 4, lower: 5$ (unau)

References

1. ^ Gardner, Alfred L. (16 November 2005). "Order Pilosa (pp. 100-103)". In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). pp. 101–102. ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=11800017. 
2. ^ http://www.thefreedictionary.com/Choloepus
3. ^ http://www.sloth-world.org/Chloepus.html
4. ^ ^{a b} Myers, Phil (2001). "Family Megalonychidae: two-toed sloths". Animal Diversity Web. University of Michigan. http://animaldiversity.ummz.umich.edu/site/accounts/information/Megalonychidae.html. Retrieved 2009-09-14. 
5. ^ Hoss, Matthias; Dilling, Amrei; Currant, Andrew; Paabo, Svante (9 Jan 1996). "Molecular phylogeny of the extinct ground sloth Mylodon darwinii". Proceedings of the National Academy of Sciences 93 (1): 181–185. doi:10.1006/mpev.2000.0860. PMID 11161746. http://www.pnas.org/content/93/1/181.abstract. Retrieved 2009-12-28. 
6. ^ White, J. L.; MacPhee, R. D. E. (2001). "The sloths of the West Indies: a systematic and phylogenetic review". In Woods, C. A.; Sergile, F. E.. Biogeography of the West Indies: Patterns and Perspectives. CRC Press. pp. 201–235. ISBN 9780849320019. http://books.google.com/books?id=kDchYICxSDsC&pg=PA201&lpg=PA201&dq=The+sloths+of+the+West+Indies:+A+systematic+and+phylogenetic+review&source=bl&ots=nE1h0uppfJ&sig=4-pNcNeA5p17LC33-Zq38BeB0iY&hl=en&ei=OgwbS625CYLOsQOy27yRBw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAoQ6AEwAA#v=onepage&q=The_sloths_of_the_West_Indies%3A_A_systematic_and_phylogenetic_review 
7. ^ ^{a b c} Dickman, Christopher R. (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 776–779. ISBN 0-87196-871-1. 
8. ^ 30% body weight

Linnaeus (1758): Systema naturae perregna tria naturae, secundum classes, ordines, genera, species cum characteribus, differentiis, syonymis, locis. Laurentii :) Salvi, 824pp.

External links

• 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