The newly-identified species of beaver, Microtheriomys articulaquaticus, represents the oldest semi-aquatic rodent in North America and the oldest amphibious beaver in the world, pushing the advent of semi-aquatic ecology in beavers by 7 million years. An ancient giant beaver. Image credit: Luke Dickey. Microtheriomys articulaquaticus lived in what is now Montana, the United States, some 30 million years ago (Oligocene epoch). The oldest previously...
