The ground sloth Megalonyx from Pleistocene deposits of the Old Crow Basin, Yukon, Canada

The bear-sized ground sloth Megalonyx, endemic to North America, was widespread during the Pleistocene, reaching as far north as Alaska, Yukon, and Northwest Territories. Twenty-two specimens collected from 10 localities in the Old Crow Basin, northern Yukon, include several bones that can be referred to Jefferson's ground sloth (Megalonyx jeffersonii) on the basis of the distinctive morphology of the upper and lower caniniform teeth. All of the Yukon specimens are relatively small, suggesting a geological age earlier than Wisconsinan-probably Sangamonian. The Alaskan, Yukon, and Northwest Territories records imply that the species occupied a broad east-west range in northwestern North America during a warm phase of the late Pleistocene.