 Eurasia and North America were many times connected by the Bering land bridge, and have very similar mammal and bird faunas, with many Eurasian species having moved into North America, and fewer North American species having moved into Eurasia (many zoologists consider the Palearctic and Nearctic to be a single Holarctic realm).See also List of extinct animals of Asia.The boreal and temperate European-Siberian region is the Palearctic's largest region, which transitions from tundra in the northern reaches of Russia and Scandinavia to the vast taiga, the boreal coniferous forests which run across the continent.