The genus "Castor" likely originated in Eurasia, the oldest fossil remains appear to be "C. neglectus" of Germany and dated 12–10 mya. The ancestors of the North American beaver would have entered North America across the Bering Land Bridge in the late Miocene. Mitochondrial DNA studies place the common ancestor of the two living species at around 8 mya. "Castor" may have competed with members of Castoroidinae, which led to niche differentiation. The Eurasian beaver may have descended from "C. praefiber". "C. californicus" from the Early Pleistocene of North America was similar to but larger than the extant North American beaver.