The Holarctic is a term used by zoologists to define the ecozone covering much of Eurasia and North America, which have often been connected by the Bering land bridge. The two regions have very similar mammal and bird fauna, with many Eurasian species having moved into North America, and fewer North American species having moved into Eurasia. More commonly, this is defined as two separate areas, the Palearctic (Eurasia) and Nearctic (North America). Ecozone is a classification system of the world first proposed by Miklos Udvardy under the name biogeographical realms for conservation purposes. ... African-Eurasian aspect of Earth Eurasia is the landmass composed of the continents of Europe and Asia. ... World map showing location of North America A satellite composite image of North America North America is a continent in the northern hemisphere, bounded on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the south by the Caribbean Sea, and on the west... The Bering land bridge, also known as Beringia, was a land bridge roughly 1600 km (1000 miles) north to south at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the ice ages. ... The Palearctic or Palaearctic is one of the eight ecozones dividing the Earth surface (see map). ... The Nearctic is one of the eight terrestrial ecozones dividing the Earths land surface. ...