The Grizzly Bear(Ursus arctos horribilis), also known as the North American brown bear or simply grizzly, is a population or subspecies of the brown bear (Ursus arctos) inhabiting North America. In addition to the mainland grizzly (Ursus arctos horribilis), other morphological forms of brown bear in North America are sometimes identified as grizzly bears. These include three living populations—the Kodiak bear (Ursus arctos middendorffi), the Kamchatka bear (Ursus arctos beringianus), and the peninsular grizzly (Ursus arctos gyas)—as well as the extinct California grizzly (Ursus arctos californicus†) and Mexican grizzly (formerly Ursus arctos nelsoni†). On average, grizzly bears near the coast tend to be larger while inland grizzlies tend to be smaller. The Ussuri brown bear (Ursus arctos lasiotus), inhabiting the Ussuri Krai, Sakhalin, the Amur Oblast, the Shantar Islands, Iturup Island, and Kunashir Island in Siberia, northeastern China, North Korea, and Hokkaidō in Japan,is sometimes referred to as the "black grizzly", although it is no more closely related to North American brown bears than other subspecies of the brown bear around the world.
Brown bears originated in Eurasia, and first migrated to North America between 177,000 YBP and 111,000 YBP. Most grizzly bears belong to this initial population of North American brown bear (clade 4), which continues to be the dominant mitochondrial grouping south of subarctic North America. Genetic divergences suggest brown bears first migrated south during MIS-5 (92,000 - 83,000 YBP) upon the opening of the ice-free corridor, with the first fossils being near Edmonton (26,000 YBP). Other mitochondrial lineages appear later- the Alexander and Haida Gwaii archipelagoes have an endemic lineage, which first appears around 20,000 YBP. After a local extinction in Beringia 33,000 YBP, two closely related lineages repopulated Alaska and northern Canada from Eurasia after the Last Glacial Maximum (25,000 YBP). In the 19th century, the grizzly was classified as 86 distinct species. By 1928 only seven grizzly species remained, and by 1953, only one species remained globally. However, modern genetic testing reveals the grizzly to be a subspecies of the brown bear (Ursus arctos). Biologist R.L. Rausch found that North America has but one species of grizzly. Therefore, everywhere it is the "brown bear"; in North America, it is the "grizzly", but these are all the same species, Ursus arctos