Castoridae

Castoridae is a family of rodents that includes two living species of beavers and their fossil relatives. Currently, only the genus Castor survives; extinct genera like Castoroides and Trogontherium were giant beavers that lived during the Late Pleistocene.

Castorids are medium-sized, semiaquatic mammals with webbed hind feet and flattened, scaly tails, allowing them to swim effectively. They live in small family groups around lodges and dams made of sticks and mud. As herbivores, they feed on leaves and grasses in summer and woody plants in winter.

The earliest castorids, such as Agnotocastor from the late Eocene and Oligocene, established behaviors that later evolved in species like Palaeocastor from the Miocene. Palaeocastor dug deep corkscrew-shaped burrows. In the Pleistocene, larger forms like Trogontherium in Europe and Castoroides in North America emerged, with Castoroides being comparable in size to a black bear but with a relatively small brain.