The giant beaver that lived in North America until roughly 10,000 years ago was the giant beaver, a member of the extinct genus Castoroides.
Castoroides was a Pleistocene rodent that occupied wetlands across much of North America. It was far larger than a living beaver: typical estimates put its length near 1.9 meters, with the largest individuals reaching roughly 2.2 meters in some modern summaries. Its bear-sized body could weigh around 90 to 125 kilograms.
Despite its familiar name, the giant beaver was not simply an oversized version of today’s beavers. It belonged to a separate extinct lineage, and its anatomy suggests a different lifestyle. Stable-isotope evidence indicates that it probably ate submerged aquatic plants rather than relying heavily on tree bark. There is also no strong evidence that it built dams or lodges like modern beavers.
The genus survived into the closing stages of the Ice Age. Young specimens from New York overlap in age with Paleo-Indian populations, but no clear evidence shows that humans hunted or butchered giant beavers. Climate change, wetland shifts, and ecological competition may all have contributed to their disappearance.