Megalonychidae is a group of sloths including the extinct Megalonyx and the living two toed sloths. Megalonychids first appeared in the early Oligocene, about 35 million years ago, in southern Argentina (Patagonia), and spread as far as the Antilles by the early Miocene. Megalonychids first reached North America by island-hopping, about 9 million years ago, prior to the formation of the Isthmus of Panama. Some lineages of megalonychids increased in size as time passed.