The First Reported Pleistocene Beaver, Castor fiber (Castoridae, Rodentia), from the Gobi Altai Region of Mongolia

Here, we report a fragmentary Castor fiber (Linnaeus, 1758) proximal left ulna from Tsagaan Agui Cave (Gobi Altai Mountains, southern Mongolia). This constitutes the first fossil evidence of this rodent from Mongolia. The Eurasian beaver is considered extinct in the Gobi Desert but fossilized remains recovered from cave deposits provide evidence that adequate habitat conditions for C. fiber existed in the Gobi Desert during some periods of the Pleistocene. Fossil C. fiber remains are relatively rare in neighboring regions including Siberia and the Russian Far East. Here, we also review the geographical distribution of fossil C. fiber in Central Asia, southern and eastern Siberia, and the Russian Far East.