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 inhabiting North America. In addition to the mainland grizzly (Ursus arctos horribilis), other forms of brown bear are sometimes identified as grizzly bears. These include three living populations—the Kodiak bear (U. a. middendorffi), the Kamchatka bear (U. a. beringianus), and the peninsular grizzly (U. a. gyas)—as well as the extinct California grizzly (U. a. californicus†) and Mexican grizzly (formerly U. a. nelsoni†). The Ussuri brown bear (U. a. lasiotus), inhabiting parts of northeast Asia, 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.
Classification
Meaning of "grizzly" Meriwether Lewis and William Clark first described it as grisley, which could be interpreted as either "grizzly" (i.e., "grizzled"—that is, with grey-tipped hair) or "grisly" ("fear-inspiring", now usually "gruesome"). The modern spelling supposes the former meaning; even so, naturalist George Ord formally classified it in 1815 as U. horribilis for its character.
Evolution and genetics
Phylogenetics Several studies have been conducted on the genetic history of the grizzly bear. Classification has been revised along genetic lines. There are two morphological forms of Ursus arctos: the grizzly and the coastal brown bears, but these morphological forms do not have distinct mtDNA lineages. The genome of the grizzly bear was sequenced in 2018 and found to be 2,328.64Mb (megabase pairs) in length and contain 30,387 genes.
Ursus arctos Brown bears originated in Eurasia, and first migrated to North America between 177,000 BP ~ 111,000 BP. 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 BP) upon the opening of the ice-free corridor, with the first fossils being near Edmonton (26,000 BP). Other mitochondrial lineages appear later- the Alexander and Haida Gwaii archipelagoes have an endemic lineage, which first appears around 20,000 BP. After a local extinction in Beringia ~33,000 BP, two closely related lineages repopulated Alaska and northern Canada from Eurasia after the Last Glacial Maximum (>25,000 BP). 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.
Subspecies in North America In 1963, Rausch reduced the number of North American subspecies to one, Ursus arctos middendorffi. Further testing of Y-chromosomes is required to yield an accurate new taxonomy with different subspecies. Coastal grizzlies, often referred to by the popular but geographically redundant synonym of "brown bear" or "Alaskan brown bear," are larger and darker than inland grizzlies, which is why they, too, were considered a different species from grizzlies. Kodiak grizzly bears were also at one time considered distinct. Therefore, at one time the thought was that there were five different "species" of brown bear, including three in North America. It remains an open question how many subspecies of Ursus arctos are present in North America. Traditionally, the following have been recognized alongside U. a. horribilis proper: Alaskan brown bear (U. a. alascensis), California grizzly bear (U. a. californicus), Dall Island brown bear (U. a. dalli), the Alaska Peninsula brown bear (U. a. gyas), Kodiak bear (U. a. middendorffi), Mexican grizzly bear (U. a. nelsoni), ABC Islands bear (U. a. sitkensis), and Stickeen brown bear (U. a. stikeenensis). One study based on mitochondrial DNA recovered no distinct genetic groupings of North American brown bears, implying that previous grizzly bear subspecies designations are unwarranted and these bears should all be considered populations of U. a. horribilis. The only genetically anomalous grouping was the ABC Islands bear, which bears genetic introgression from the polar bear. A formal taxonomic revision was not performed, however, and the implied synonymy has not been accepted by taxonomic authorities. Furthermore, a handful of studies have suggested that certain Alaskan brown bears, including the Kodiak and Alaskan Peninsula grizzly bears, are members of a Eurasian brown bear lineage, more closely related to Siberian brown bear populations than to other North American brown bears. Until the systematics of North American brown bears is studied in more depth, other North American subspecies have been provisionally considered separate from U. a. horribilis.
Appearance
Size
Grizzly bears are some of the largest subspecies of brown bear, only being beaten by the Kamchatka brown bears and the Kodiak bears. Grizzly bears vary in size depending on timing and populations. The largest populations are the coastal grizzlies in the Alaskan peninsula, with males weighing 389 kilograms (858 lb) and females weighing 207 kilograms (456 lb). The populations in northern interior Canada are much smaller, with males weighing 139 kilograms (306 lb) and females weighing 95 kilograms (209 lb). This is actually similar to the American black bear population of the area. Average total length in this subspecies is between 198 cm (78 in) and 240 cm (94 in), with an average shoulder height of 102 cm (40 in) and hindfoot length of 28 cm (11 in). Newborn bears may weigh less than 500 g (18 oz).
Characteristics
Although variable in color from blond to nearly black, grizzly bear fur is typically brown with darker legs and commonly white or blond-tipped fur on the flank and back. Grizzly bears overlap with Black Bears in range, but numerous factors can differentiate the two:
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