Ground sloths are a diverse group belonging to superorder Xenarthra, which also includes extinct pampatheres and glyptodonts, as well as living tree sloths, anteaters, and armadillos. One of the four major eutherian radiations, this superorder evolved in isolation in South America while it was an island continent during the Paleogene and Neogene. The family to which "Megatherium" belongs, Megatheriidae, is related within superfamily Megatheroidea to the extinct families Nothrotheriidae and Megalonychidae, and to living three-toed sloths of family Bradypodidae, as deduced recently from collagen and mitochondrial DNA sequences obtained from subfossil bones.