extinct genus of giant beavers found as fossils in Pleistocene deposits in North America (the Pleistocene Epoch began 1,600,000 years ago and ended 10,000 years ago). Castoroides attained a length of about 2.5 m (7.5 feet). The skull was large and the gnawing teeth strongly developed. In Europe, a similar form of giant beaver, Trogontherium, paralleled the development of Castoroides.