[3][5] The skull structure of the giant beaver suggests that it participated in extended underwater activity, thanks to the ability to take more oxygen into its lungs.

In Canada, fossils of this species are commonly found in the Old Crow Basin, Yukon, and single specimens are known from Toronto, Ontario and Indian Island, New Brunswick.

[1][14] Specimens from the southeastern U.S. have been placed in a separate species, Castoroides dilophidus, based on differences in premolar and molar features.

Stable isotopes suggest that Castoroides probably predominantly consumed submerged aquatic plants, rather than the woody diet of living beavers.

This roughly coincides with the arrival of the Clovis culture in the region—who rapidly colonized the area by 12,800 years ago—as well the beginning of an aridity trend.

It has been long debated if humans ("overkill hypothesis") or climate change had a bigger effect in the extinction event, but they took several thousands of years to completely die out.

Radiocarbon dates from Ohio and New York indicate that the lowlands south of the Great Lakes was home to the last isolated Castoroides populations when it disappeared from eastern North America shortly before the Pleistocene-Holocene transition event, bringing the complete extinction of the genus.

Differing scientific theories exist considering whether the extinction of Castoroides was caused by hunting by the early human arrivals in the Americas.

[29][30] In 1972, American ethnologist Jane Beck hypothesized C. ohioensis was the basis of an Algonquin myth where a gargantuan beaver created a dam so high on the Saint John River, the lake behind it almost reached the sea.

Glooscap chased the monster upstream, creating several islands in the river while attempting to strike the beaver through the ice.

[31] Several versions of an Anishinaabe story tell of "giant beavers" who "walked upright and stood as tall as the tallest man.

"[32] Many scholars believe that stories like these could be evidence from the oral tradition of North American First Nations people encountering C. ohioensis or, at the very least, their fossils.