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''Choloepus'' is a genus of mammals of Central and South America, within the family Megalonychidae consisting of two-toed sloths.〔(【引用サイトリンク】title=Choloepus )〕 The two species of ''Choloepus'' (which means "lame foot"〔(【引用サイトリンク】title=Sloth-World.org )〕), Linnaeus's two-toed sloth (''Choloepus didactylus'') and Hoffmann's two-toed sloth (''Choloepus hoffmanni''), are the only surviving members of the family Megalonychidae.〔 ==Relation to the three-toed sloth== Although similar to the somewhat smaller and generally slower-moving three-toed sloths (''Bradypus''), the relationship between the two genera is not close. Recent phylogenetic analyses support analysis of morphological data from the 1970s and 1980s, suggesting the two genera are not closely related and each adopted its arboreal lifestyle independently. It is unclear from which, if any, ground-dwelling sloth taxa the three-toed sloths evolved; 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. Though data has been collected on over 33 different species of sloths just by analyzing bone structures, many of the relationships between clades on a phylogenetic tree are unknown. Both types tend to occupy the same forests; in most areas, a particular species of three-toed sloth and a single species of the larger two-toed type will jointly predominate. Each genus of sloth has a common ancestor, but what that ancestor was, when it existed, and many of its traits remain virtually unknown. There is relatively little evidence to support the hypothesis of diphyly and only a small amount of data to study overall. In fact, most of the evidence to support the hypothesis of diphyly is still heavily based on the same trait that cause the hypothesis to be suggested; the structure of the inner ear.〔Pant et al., 2014〕 One of the largest problems that exists when attempting to identify clades of modern extant tree sloths is the issue of missing links between surviving, living species and their unidentified common ancestors. There are several families of extinct sloths, about which very little is known. This missing information causes large holes in phylogenetic trees and makes tracing paths of evolution a daunting task. As a result, there are many versions of the phylogenetic tree that would describe the evolution and relationship between sloths, most of which conclude that convergent evolution is the likely mechanism that resulted in today’s genera of tree sloths. Despite a couple of discrepancies in DNA sequencing, it is largely accepted that extant tree sloth species of the genera ''Choloepus'' and ''Bradypus'' do not share a recent common ancestor, making them diphyletic to one another and indicating similarities through convergent evolution. This means that the two extant genera evolved analogous traits, such as locomotion methods, size, habitat, and many other traits independently from one another as opposed to from their last common ancestor. If the theory of convergent evolution between the two species were accepted as true, that would make sloths “one of the most striking examples of convergent evolution known among mammals”.〔Gaudin et al., 2004〕 In order to further support this theory, there would need to be more information and data gathered about intermediate species between the extant species and the common ancestor, which is estimated to have gone extinct over 30 million years ago.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Two-toed sloth」の詳細全文を読む スポンサード リンク
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