Polar bear

The polar bear (Ursus maritimus) is a bear native to the Arctic Ocean and its surrounding seas. It is the world's largest carnivore species found on land. It's also the largest bear, together with the omnivore Kodiak bear which is approximately the same size, but which is a subspecies of the brown bear that is normally smaller than the polar bear. An adult male weighs around 400–680 kg (880–1,500 lb), while an adult female is about half that size. Although it is closely related to the brown bear, it has evolved to occupy a narrow ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet. Although most polar bears are born on land, it spends most of its time at sea, hence its name meaning "maritime bear", and can hunt consistently only from sea ice, spending much of the year on the frozen sea.

The polar bear is classified as a vulnerable species, with 5 of the 19 polar bear subpopulations in decline. For decades, unrestricted hunting raised international concern for the future of the species; populations have rebounded after controls and quotas began to take effect. For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and the hunting of polar bears remains important in their cultures.

The IUCN now lists global warming as the most significant threat to the polar bear, primarily because the melting of its sea ice habitat reduces its ability to find sufficient food. The IUCN states, "If climatic trends continue polar bears may become extirpated from most of their range within 100 years." On May 14, 2008, the United States Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act.

Naming and etymology

Constantine John Phipps was the first to describe the polar bear as a distinct species. He chose the scientific name Ursus maritimus, the Latin for 'maritime bear', due to the animal's native habitat. The Inuit refer to the animal as nanook, (transliterated as nanuuq in the Inupiat language, and nanuuk in Siberian Yupik.) The bear is umka in the Chukchi language. In Russian, it is usually called Белый Медведь (Bely Medved, the White Bear), though an older word still in use is Ошкуй (Oshkuy, which comes from the Komi Oski, "bear"). In Quebec French, the polar bear is referred to as Ours polaire. The polar bear was previously considered to be in its own genus, Thalarctos. However, evidence of hybrids between polar bears and brown bears, and of the relatively recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed.

Taxonomy and evolution

Polar bears depend on sea ice as a platform for hunting seals. Large feet and short, stocky claws are adaptations to this environment.

The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. The Ursinae subfamily originated approximately 4.2 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear, Ursus arctos, roughly 200,000 years ago. The oldest known polar bear fossil is less than 100,000 years old. Fossils show that between ten to twenty thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene.

More recent genetic studies have shown that some clades of brown bear are more closely related to polar bears than to other brown bears, meaning that the polar bear is not a true species according to some species concepts. In addition, polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids, indicating that they have only recently diverged and are genetically similar. However, as neither species can survive long in the other's ecological niche, and with distinctly different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.

When the polar bear was originally documented, two subspecies were identified: Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter Simon Pallas in 1776. This distinction has since been invalidated.

One fossil subspecies has been identified. Ursus maritimus tyrannus—descended from Ursus arctos—became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.

Polar bears investigate the submarine USS Honolulu 280 miles (450 km) from the North Pole.