Megalonychidae

Temporal Range:  35 Mya - 0 Mya

OVERVIEW

                      Megalonychidae is a group of sloth that includes the extinct ground sloth and the living two toed sloth. Megalonychidae first appeared in the early Oligocene, about 35 million years ago, in Southern Argentina (Patagonia), and 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.
                        Megalonychid ground sloths went extinct in North and South America around the end of the Pleistocene and in the Antilles apparently by about 5000 BP, living two-toed sloths of genus Choloepus as the only surviving member of the family.

EVOLUTION

                        Megalonyx means giant claws. Megalonyx is widespread North American genus that lived past in the close of the last Ice Glaciation. Remains of Megalonyx have been found as far north as Alaska to the Yukon. Ongoing excavations at Tarkio Valley in southwest Iowa may reveal something of the familial life of Megalonyx. An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations.
                          The earliest known North American megalonychid, Pliometanastes protistus, lived in Florida and the southern U.S. about 9 million years ago, and is believed to have been the predecessor of Megalonyx. Several species of Megalonyx have been named; actually most of the good specimen described as different species. A broader perspective on the group, accounting for age, sex, individual and geographic differences, indicates that only three species are valid (M. leptostomus, M. wheatleyi, and M. jeffersonii) in the late Pliocene and Pleistocene of North America. Although work by McDonald lists five species.