Ground sloth

Ground sloths Temporal range: 35–0.005 Ma PreꞒ Ꞓ O S D C P T J K Pg N Late Eocene – Holocene
American Museum of Natural History mounts of (from left) Megalocnus rodens, Scelidotherium cuvieri, Megalonyx wheatleyi, Glossotherium robustus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Pilosa
Suborder:	Folivora
Families
†Megalocnidae (in part) †Megalonychidae †Megatheriidae †Nothrotheriidae †Mylodontidae †Scelidotheriidae

Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. They varied widely in size with the largest, belonging to genera Lestodon, Eremotherium and Megatherium, being around the size of elephants. Ground sloths represent a paraphyletic group, as living tree sloths are thought to have evolved from ground sloth ancestors.

The early evolution of ground sloths took place during the late Paleogene and Neogene of South America, while the continent was isolated. At their earliest appearance in the fossil record, they were already distinct at the family level. Sloths dispersed into the Greater Antilles during the Oligocene, and the presence of intervening islands between the American continents in the Miocene allowed a dispersal of some species into North America. They were hardy as evidenced by their high species diversity and their presence in a wide variety of environments, extending from the far south of Patagonia (Cueva del Milodón Natural Monument) to Alaska.^[1][2][3] Sloths, and xenarthrans as a whole, represent one of the more successful South American groups during the Great American Interchange after the connection of North and South America during the late Pliocene with a number of ground sloth genera migrating northwards. One genus, Thalassocnus, even adapted for marine life along the Pacific coast of South America during the late Miocene and Pliocene epochs.

Ground sloths, which were represented by over 30 living species during the Late Pleistocene, abruptly became extinct on the American mainland as part of the end-Pleistocene extinction event around 12,000 years ago, simultaneously along with the majority of other large animals in the Americas. Their extinction has been posited to be the result of hunting by recently arrived humans and/or climate change.^[4][5] A number of kill sites are known where humans butchered ground sloths dating just prior to their extinction.

The Caribbean ground sloths, the most recent survivors, lived on Cuba and Hispaniola, possibly until 1550 BCE. However, radiocarbon dating suggests an age of between 2819 and 2660 BCE for the last occurrence of Megalocnus in Cuba.^[6] 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.^[7]