Castor californicus

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Castor californicus was an extinct beaver that lived in western North America from the late Miocene to the early Pleistocene. It was first found in the Kettleman Hills of California and was larger than the modern North American beaver (Castor canadensis). A distinctive feature is that it had three folds in the inner enamel epithelium of its teeth, a trait not seen in other Castor species. It is the earliest known Castor to appear in North America. It had short nasal passages and a wide back of the skull, with a more spread-out coronoid process. Its pterygoid and neck muscles were relatively large, giving it extra strength. Fossils show some variation between individuals. Castor californicus had short thigh bones and long hind feet, helping it swim, and broad metatarsals that aided both swimming and digging. These traits would have helped it move well in water compared with other beavers.