The Tagay vertebrate fauna (Olkhon Island, Lake Baikal, Russia) dated to the late Early Miocene yielded a diverse association of sciurine rodents, including flying squirrel Hylopetes sp., tree squirrels Sciurus cf. lii, Sciurus sp., and Blackia cf. miocaenica, and a numerically dominant small marmotine Miospermophilus debruijni. The presence of flying and tree squirrels indicates the presence of wooded biotopes. The record of Blackia is remarkably distant (more than 4000 km) from the nearest synchronous records in western Asia (Anatolia) and Eastern Europe thus implying a continuous distribution range of this genus stretching through the middle latitudes of the Holarctic and likely marking the continental belt of temperate forests in late Early Miocene. Marmotines of North American origin document direct faunal communication between temperate faunas of the Old and New Worlds at that time.