How did mammals migrate from Eurasia to North America during the Miocene?

During the Miocene Epoch, mammals migrated from Eurasia to North America primarily by crossing the Bering Land Bridge, a connection that linked Siberia and Alaska.12

While the Thulean Land Bridge—which had previously connected North America and Europe—was severed during the Eocene, the connection between Asia and Alaska remained intact, facilitating repeated migrations throughout the Oligocene and Miocene epochs. This route allowed for significant faunal exchanges; for instance, the early Miocene saw a wave of immigration into North America that included bear-dogs, European rhinoceroses, weasels, and various deerlike mammals. By the middle of the Miocene, mastodons also reached North America via these northern connections.1

These migrations were part of broader evolutionary shifts driven by changing climatic conditions, including cooling and drying trends that expanded grassland ecosystems and spurred the diversification of grazing mammals.1