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Giant sloth wallpaper3/20/2024 ![]() ![]() This small size also enabled them a degree of arboreality. ![]() Some West Indian island species were as small as a large cat their dwarf condition typified both tropical adaptation and their restricted island environment. The first species of these were small and may have been partly tree-dwelling, whereas the Pliocene (about 5 to 2 million years ago) species were already approximately half the size of the huge Late Pleistocene Megalonyx jeffersonii from the last ice age. Some lineages of megalonychids increased in size as time progressed. Megalonychids first reached North America by island-hopping, prior to the formation of the Isthmus of Panama. The megalonychid ground sloths first appeared in the Late Eocene, about 35 million years ago, in Patagonia. Paleontologists assign more than 80 genera of ground sloths to multiple families. 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. However, radiocarbon dating suggests an age of between 28 BCE for the last occurrence of Megalocnus in Cuba. The Caribbean ground sloths, the most recent survivors, lived in the Antilles, possibly until 1550 BCE. A number of kill sites are known where humans butchered ground sloths dating just prior to their extinction. Their extinction has been posited to be the result of hunting by recently arrived humans and/or climate change. Ground sloths abruptly became extinct on the American mainland as part of the Quaternary extinction event at the end of the Pleistocene, around 12,000 years ago along with most other large mammals in the Americas. One genus, Thalassocnus, even adapted for marine life along the Pacific coast of South America during the late Miocene and Pliocene epochs. 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. 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. ![]() At their earliest appearance in the fossil record, the ground sloths were already distinct at the family level. The early evolution of ground sloths took place during the late Paleogene and Neogene of South America, while the continent was isolated. Ground sloths are a paraphyletic group, as living tree sloths are thought to have evolved from ground sloth ancestors. Ground sloths varied widely in size, with the largest genera Megatherium and Eremotherium being around the size of elephants. Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. American Museum of Natural History mounts of (from left) Megalocnus rodens, Scelidotherium cuvieri, Megalonyx wheatleyi, Glossotherium robustus ![]()
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