page_title: Ground sloth
section_title: Megatheriidae
hierarchical_section_title: Ground sloth / Families / Megatheriidae
caption_attribution_description: Ground Sloth (Eremotherium) fossil at the National Museum of Natural History, Washington, D.C.
context_page_description: 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 BC. However, radiocarbon dating suggests an age of between 2819 and 2660 BC for the last occurrence of Megalocnus in Cuba. Ground sloths had been extinct on the mainland of North and South America for 10,000 years or more. 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.
  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.
context_section_description: The megatheriid ground sloths are relatives of the megalonychids; these two families, along with the family Nothrotheriidae, form the infraorder Megatheria. Megatheriids appeared later in the Oligocene, some 30 million years ago, also in South America.  The group includes the heavily built Megatherium (given its name 'great beast' by Georges Cuvier) and Eremotherium. The skeletal structure of these ground sloths indicates that the animals were massive.  Their thick bones and even thicker joints (especially those on the hind legs) gave their appendages tremendous power that, combined with their size and fearsome claws, provided a formidable defense against predators.
  The earliest megatheriid in North America was Eremotherium eomigrans which arrived 2.2 million years ago, after crossing the recently formed Panamanian land bridge. With more than five tons in weight, 6 meters in length, and able to reach as high as 17 feet (5.2 m), it was larger than an African bush elephant bull. Unlike relatives, this species retained a plesiomorphic extra claw. While other species of Eremotherium had four fingers with only two or three claws, E. eomigrans had five fingers, four of them with claws up to nearly a foot long.
caption: Fossil Eremotherium skeleton, National Museum of Natural History, Washington, DC.
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