Giant Beaver | The Canadian Encyclopedia


Giant Beaver

The giant beaver (Castoroides ohioensis) is an extinct rodent that lived in North America between 1.4 million and 10,000 years ago. It was a distant cousin to modern beavers, but in many ways may have been more similar to modern capybaras. The giant beaver was one of the largest rodents ever to roam the Earth, and one of approximately 30 extinct genera of beavers. Only two beaver species survive today: the North American beaver and the Eurasian beaver. The giant beaver received its scientific name after remains were found in 1837 in Ohio. In Canada, giant beaver fossils have been found on Indian Island, New Brunswick; in Toronto and near Highgate, Ontario; and in Old Crow Basin, Yukon. They live on in the oral history of many Indigenous peoples, including the Innu, Seneca, eastern Cree, Chippewa and Vuntut Gwitchin.


In addition to C. ohioensis, another similar species lived during same period: C. dilophidus. The former mostly lived from southern Canada to the southern United States, but sometimes as far northwest as Yukon and Alaska. The latter was confined to the southeastern United States. Despite what their name suggests, giant beavers are not closely related to modern beavers. The last ancestor they had in common lived about 20 million years ago.

Physical Description

Giant beavers could grow to more than 2 m long, not including their tail, and could weigh in excess of 100 kg. Their tail could reach 65 cm long, but was proportionally narrower than a modern beaver’s. With large hind feet but short limbs overall, they were more adapted to aquatic life than movement on land. Their front teeth had blunt tips, prominent ridges along their outer surface, and could grow up to 15 cm long. Studies also show that giant beaver brains were proportionally smaller and smoother than those of modern beavers. This suggests they may not have been as capable of complex tasks.

Giant Beaver
Giant beavers (Castoroides ohioensis) grew to more than 2 m long, not including their tail. For comparison, modern beavers grow as long as 1.3 m, tail included. 

Geographic Distribution and Habitat

Giant beavers lived in places throughout Canada and the United States. However, during the last ice age they were concentrated just south of the Great Lakes, in Illinois and Indiana. It is likely that during warmer, interglacial periods giant beavers migrated north seeking the cooler temperatures they were accustomed to. The retreating ice sheets also left behind lakes and wetlands and giant beavers took advantage of these new habitats. Researchers have found fossils as far north as Old Crow Basin, Yukon, and Porcupine River, Alaska. Most remains are found in ancient swamps, lakes or ponds. It is likely that these aquatic places were the giant beaver’s favourite habitats.


Scans have revealed a cavity in the giant beaver’s skull that may have been used to produce sounds. While modern beavers also make noises, they do not have the same skeletal cavity. Little is known about other giant beaver behaviours, such as social and mating habits.

Diet and Dams

Researchers are still uncertain about the giant beaver’s diet and lifestyle. Some think it ate aquatic plants almost exclusively and did not build dams or lodges. Others believe it ate mostly terrestrial plants and did build such structures. Although the location of fossils shows the giant beaver preferred aquatic habitats, there is little evidence to suggest engineering behaviour similar to modern beavers. For example, the angle of the giant beaver’s front teeth does not seem adapted to tree cutting. Similarly, while branches have been found near giant beaver fossils before, there is disagreement as to whether their extremities match the shape of the giant beaver’s front teeth. Chemical and isotopic analyses of fossils have shown no sign of wood in the giant beaver’s diet. However, these analyses do not exclude dam-building entirely. Despite inconclusive evidence, tree harvesting has occurred in certain branches of the Castoridae family since the Miocene epoch (23 million–5.3 million years ago), and a lodge that may have been built by giant beavers was found in Ohio in 1912. Whether giant beavers were builders or not remains an open question.


The most recent fossils found show that giant beavers went extinct towards the end of the Pleistocene epoch, about 10,000 years ago. While scientists aren’t sure what caused their extinction, it is almost certainly related to changing climate conditions in that period, when many megafauna species went extinct. The wetlands in which giant beavers lived began to dry up, starting in the southern part of their range. Because they may not have been able to modify their environment like a modern beaver would, they were forced to move north. However, their bodies were poorly adapted to land travel, and many struggled to relocate.

Other studies suggest the mix of causes leading to the giant beaver’s extinction were different. For example, the changing climate also shifted the timing of precipitation, which may have hampered the growth of the plants giant beavers ate. Other factors, such as increased competition for food with other semi-aquatic rodents, may have also played a role.

Did you know?
In an eastern Cree creation story, the Trickster Wisagatcak built a dam to trap the Giant Beaver. As Wisagatcak readied his spear, Muskrat bit him, causing the spear to miss. The next day Wisagatcak decided to break the dam. Though water flowed out of the broken dam, the level of the creek didn’t fall. The giant beavers had worked their magic. Wisagatcak built a raft, gathering the animals swimming in the water around him. The water continued to rise until there was no land left. Then, Wisagatcak made his own magic. He called on Wolf, who ran around the raft with a ball of moss in his mouth. As he ran, the ball grew and gathered earth. Eventually, Wolf put the ball down and they danced around it. As they danced the earth continued to grow, eventually forming the whole world.

Relationship with Humans

Very little evidence has been found to suggest that humans hunted giant beavers, although it is possible they did. For example, researchers found human artifacts alongside giant beaver remains in Sheriden Cave, Ohio. Some Indigenous peoples may have used giant beaver teeth as woodworking chisels, and references to giant beavers are found in the oral history of various First Nations. An eastern Cree creation tale features a giant beaver, for example, and the animal makes an appearance in the Innu Tale of Tshakapesh. It can also be found in stories from the Vuntut Gwitchin of Old Crow, the Chippewa and the Seneca.

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