Megatherium's ancestors lived in South America and eventually began to migrate North once sea level dropped and land appeared between North and South America, forming a passage. It is part of the Xenarthrans group which contains Armadillos, Sloths, and Anteaters. The Xenarthrans originated in the Cretaceous on the Southern continent of Gondwanaland. The name 'Xenarthra' refers to extra articulations between the vertebrates which all the animals in this group share. These articulations give the back of the animal greater strength but they are less able to twist and turn.