Pliometanastes and Thinobadistes were the first of the giant sloths to appear in North America, the former around 9 million years ago.[2] Both were in North America before the
Panamanian Land Bridge formed around 2.7 million years ago, which led to the main pulse of the
Great American Interchange. It is then reasonable to presume that the ancestors of Pliometanastesisland-hopped across the
Central American Seaway from
South America, where ground sloths arose.[3]
Pliometanastes gave rise to Megalonyx. Their closest extant relatives, based on molecular results (which clash with earlier conclusions derived from morphology) are the extant
arborealthree-toed sloths (Bradypus).[4][5]
P. protistus has been estimated to weigh 851 kg.[6]
Taxonomy
Pliometanastes was named by Hirschfeld and Webb (1968). Its type is Pliometanastes protistus. It was assigned to Megalonychidae by Hirschfeld and Webb (1968) and Carroll (1988).[7][8]