Evolution
The ground sloths, as with all other xenarthrans, evolved in isolation in South America, while it was an island continent during the Paleogene. During the Pliocene, the Central American Isthmus formed, causing the Great American Interchange, and a mass extinction of much of the indigenous South American megafauna. Ground sloths were largely unaffected and continued to thrive in spite of competition from the northern immigrants. In fact ground sloths were among the various South American animal groups to migrate northwards into North America, where they remained and flourished until the late Pleistocene.
The rhinoceros-sized Promegatherium of the Miocene is suggested to be the ancestor of Megatherium. The oldest (and smallest) species of Megatherium is M. altiplanicum of Pliocene Bolivia. It was very similar to Promegatherium, and was also about the size of a rhinoceros. Species of Megatherium became larger and larger, with the largest species, M. americanum of the late Pleistocene, reaching the size of an African Elephant.
Read more about this topic: Megatherium
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