ABSTRACT
The castorid dental material described in this paper derives from Miocene, fossiliferous deposits of the Baikal rift valley, exposed at Tagay Bay on Olkhon Island in the Lake Baikal, in eastern Siberia. It consists of maxillary fragments and isolated upper and lower teeth of the small trogontheriine beaver Euroxenomys minutus (von Meyer, 1838). It is the first record of the species in Asia and at the same time the northernmost occurrence of Eurasian Miocene beavers. The magnetostratigraphic correlation of the Tagay -1 section, indicates a late Burdigalian, Early/early Middle Miocene age of ~16.5 to ~16.3 Ma that corresponds to the Mammalian Neogene zone MN4/5. The presence of E. minutus in Tagay is an indicator for an Orleanian European-Siberian bioprovince during the Mid-Miocene Climate Optimum, and for a continuous belt of humid, warm-temperate to subtropical forests, stretching from Europe to Siberia, and probably further to East and South-Eastern Asia. In Eurasia, beaver remains are an indicator of permanent water bodies, which is in agreement with the palaeoenvironment of the Tagay locality.