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The polar bear or White bear (Ursus maritimus, formerly Thalarctos maritimus) is a species of Mammal Carnivore of the family of bears (Ursidae).[2] Rivals with his relative, the Kodiak bear (Ursus arctos middendorffi), by the title of Earth's largest terrestrial Carnivore . He lives in the polar medium and freezing areas of the Northern hemisphere. It is the only superdepredador of the Arctic.Index[hide]
1 Name and etymology
2 Taxonomy and evolution
3 Description
4 Playback
5 Populations
6 Power supply
7 Threats
8 See also
9 References
10 Bibliography
11 External links


[Edit] Name and etymologyConstantine John Phipps was the first scientist who describes the polar bear as a distinct species. He prefers the scientific name Ursus maritimus, from the latin "maritimebear" due to the native habitat of this animal. The inuit regard this animal as nanook (transliterated like nanuq in the Inupiaq language).

[Edit] Taxonomy and evolution
Polar bears used the plates of ice as a platform to hunt seals. Members thick, short and sharp claws and long are adapted for this purpose.It is believed that the family, Ursidae, separated from other carnivoresapproximately 38 million years ago. The Ursinae subfamily originated approximately 4.2 million years ago. According to the evidence fossil and DNAanalyses, only 150,000 years ago took place the divergence of the species and the brown bear (Ursus arctos )).[3] The fossil of oldest polar bear that is known, dates from about 130,000 to 110,000 years ago and was found in the Island Prince Charles-Forlandin2004.[3] Fossils show that it makes between 10,000 and 20,000 years, the molars of polar bear differed significantly with respect to the brown bear. It is possible that the species has originated from a population isolated from grizzly bears, subjected to a strong genetic pressure during the glaciations of the Pleistocene.[4]

Genetic studies subsequently show that even some populations of brownbears are more related to the polar bear, who with others of the same species;[5] This implies that the polar bear does not meet some of the definitions of species.[6] In addition, the two species can reproduce and fertile hybrids (Grolares),[4] [7] indicating his recent divergence and their genetic similarity.[8] However, are considered separate species because none of the two species can survivelong term in the ecological niche of the other, they have different morphological and phenotypic; metabolism, behavior and other social behavior.[8]

When the species was described two subspecieswere identified: Ursus maritimus maritimus (Constantine J. Phipps in 1774) and Ursus maritimus marinus (Peter Simon Pallas in 1776).[9] These subspecies are not currently valid.

It is registration ofa fossil subspecies, Ursus maritimus tyrannus, who was a descendant of Ursus arctos and became extinct during the Pleistocene. This subspecies was rather larger than the existing species.[4]

[Edit] DescriptionIt presents a profile more elongated than other bears and more developed legs, both for walking and swimming long distances. The ears and tail are very small, to better maintain bodyheat, like in many other Arctic mammals. A thick layer of subcutaneous fat and dense fur, which in reality is not white, but translucent, formed by thousands of hollow hairs (which when filled with air, are a good thermal insulator) also collaborate in this. Under the coat is the skin, which is black to better attract the solar radiation and thus increase body heat. Ordinary light is reflected onthe fur, normally generating the false sense of whiteness. However, at certain times and places may be yellowish or even Brown clear. The loss of body heat is very reduced, both by the coat and the color of the dermis and the thick adipose panniculus that is located under the skin and slimming only on the head, especially in the nose. During the summer these bears thin and to possess very densely...