The giant beaver (Castoroides ohioensis) was one of the largest rodents ever known. It reached a length of about 2.5 m and weighed up to an estimated 218 kg. Unlike modern beavers (Castor canadensis), giant beavers had ridged cutting teeth, deep skulls, and probably roundish, muskrat-like tails.
Fossils that are over 70,000 years old have been found in Toronto, Canada, and in the Old Crow basin of the Yukon. This animal died out with mammoths, mastodons, and ice-age horses about 10,000 years ago.