a zoogeographic region of dry land that is considered by many zoogeographers to be a division of the Holarctic region. The Nearctic Region covers the continent of North America, including the Mexican Plateau, as well as the Aleutian Islands, the Canadian Arctic Archipelago, Greenland, and Newfoundland. The fauna in the northernmost parts is similar to that of the Palearctic division of the Holarctic region. This similarity may be explained by the repeated, prolonged unions of North America and Northeastern Asia in the region of what is now the Bering Sea, which made possible a broad exchange of species.
The Nearctic Region is divided into four subregions: the Arctic, Circumboreal, Western American, and Eastern American. The first two are common to the Palearctic; the last two are often united in the Sonoran subregion. The American portion of the Circumboreal subregion is sometimes regarded as the independent Canadian subregion.