Pliometanastes
Pliometanastes is an extinct genus of giant ground sloths of the family Megalonychidae endemic to North America during the Late Miocene epoch through very early Pliocene epoch (Hemphillian in the NALMA classification). Its fossils have been found in Costa Rica and across the southern United States from California to Florida. Description. "Pliometanastes" and "Thinobadistes" were the first of the giant sloths to appear in North America, the former around 9 million years ago. 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 "Pliometanastes" island-hopped across the Central American Seaway from South America, where ground sloths arose. "Pliometanastes" gave rise to "Megalonyx". Their closest extant relatives, based on molecular results (which clash with earlier conclusions derived from morphology) are the extant arboreal three-toed sloths ("Bradypus"). 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). Fossil distribution. Sites and ages of specimens (not complete list):