3. Giant Beaver

Most commonly found in the Great Lakes region, the giant beaver was an enormous version of the water-dwelling rodent we know today. Scientifically known as Castoroides, the giant beaver lived in the Yukon and Alaska but migrated south when the weather got too cold. These large aquatic animals were the biggest beavers ever to exist on Earth.

Modern beavers weigh around 44 pounds, but Castoroides could weigh up to 276 pounds. On average, they measured between 6.2 and 7.2 feet long. Their hind legs were shorter than today’s beavers, and their hind feet were much larger. These beavers most likely spent a lot of time underwater based on their ability to take more oxygen into their lungs. Giant beavers had skulls that were much smaller than their modern counterparts, so they generally had behaviors and thoughts that were less complex.