Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. The term is used as a reference for all extinct sloths because of the large size of the earliest forms discovered, as opposed to existing tree sloths. The Caribbean ground sloths, the most recent survivors, lived in the Antilles, possibly until 1550 BCE. However, radiocarbon dating suggests an age of between 2819 and 2660 BCE for the last occurrence of Megalonyx in Cuba.[1] Ground sloths had been extinct on the mainland of North and South America for 10,000 years or more.[2] They survived 5,000–6,000 years longer in the Caribbean than on the American mainland, which correlates with the later colonization of this area by humans.[3]
Much ground sloth evolution took place during the late Paleogene and Neogene of South America, while the continent was isolated. At their earliest appearance in the fossil record, the ground sloths were already distinct at the family level. The presence of intervening islands between the American continents in the Miocene allowed a dispersal of forms into North America. A number of mid- to small-sized forms are believed to have previously dispersed to the Antilles. They were hardy as evidenced by their diverse numbers and dispersals into remote areas given the finding of their remains in Patagonia (Cueva del Milodón Natural Monument)[4] and parts of Alaska.
Sloths, and xenarthrans as a whole, represent one of the more successful South American groups during the Great American Interchange. During the interchange, many more taxa moved from North America into South America than in the other direction. At least five genera of ground sloths have been identified in North American fossils; these are examples of successful immigration to the north.
