Castoroides
Castoroides, or giant beaver, is an extinct genus of enormous, bear-sized beavers that lived in North America during the Pleistocene. Two species are currently recognized, C. dilophidus in the Southeastern US and C. ohioensis in the rest of its range. C. leiseyorum was previously described from the Irvingtonian of Florida, but is now regarded as an invalid name. All specimens previously described as C. leiseyorum are considered to belong to C. dilophidus.
Species of Castoroides were much larger than modern beavers. Their average length was approximately 1.9 m (6.2 ft), and they could grow as large as 2.2 m (7.2 ft). The weight of the giant beaver could vary from 90 kg (198 lb) to 125 kg (276 lb). This makes it the largest known rodent in North America during the Pleistocene and the largest known beaver.[2] Recent analyses suggest that they weighed less, closer to 77 kg (170 lb), but this is disputable.[3]
The hind feet of the giant beaver were much larger than in modern beavers, while the hind legs were shorter. The tail was longer and may not have been paddle-shaped as in modern beavers.[1] It can only be assumed that its feet were webbed as in modern species.[2][4] 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.[4]
One of the defining characteristics of the giant beaver was their incisors, which differed in size and shape from those of modern beavers. Modern beavers have incisor teeth with smooth enamel, while the teeth of the giant beaver had a striated, textured enamel surface.[5] Their teeth were also much larger, up to 15 cm (6 in) long.[5]
One other major difference between the giant beaver and the modern beaver is that the size of its brain was proportionally smaller. As a result, the giant beaver may have had inferior interactions in its environment, as well as less complex patterns of thoughts and behavior.[6][failed verification]
These two species of giant beaver (genus Castoroides) are not close relatives to modern beavers (genus Castor).[4]
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