Beaked whale

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Beaked whales are 21 species of toothed whales, members of the family Ziphiidae that are notable for their elongated snouts. They are the only marine mammals whose evolution is believed to have been shaped by a secondary sexual characteristic (the male's teeth). Beaked whales are the world's most extreme divers. They can dive for long periods—20 to 30 minutes is common, and 85 minute dives have been recorded—and to great depths: 1,899 metres (1,038 fathoms) and possibly more.[1] To avoid getting decompression sickness—the potentially fatal build-up of nitrogen bubbles in body tissues—they must surface slowly.[2]

Beaked whales are one of the least known groups of mammals because of their deep-sea habitat, mysterious habits, and apparent low abundance. [3] Several species have yet to be formally described or named; others are known only from remains and have never been sighted alive. Only 3–4 of the 20-odd species are reasonably well-known. Baird's and Cuvier's Beaked Whales were subject to commercial exploitation, off the coast of Japan, while the Northern Bottlenose Whale was extensively hunted in the northern part of the North Atlantic late in the 19th and early in the 20th centuries.

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Physical characteristics

Beaked whales are moderate in size, ranging from 4 to 13 metres (13 to 43 ft) and weighing from 1 to 15 tonnes (0.98 to 15 LT; 1.1 to 17 ST). Their key distinguishing feature is the presence of a 'beak', somewhat similar to many dolphins. Other distinctive features include a pair of converging grooves under the throat, and the absence of a notch in the tail fluke. Although Shepherd's Beaked Whale is an exception, most species have only one or two pairs of teeth, and even these do not erupt in females. Beaked whale species are often sexually dimorphic—one or the other sex is significantly larger. The adult males often possess a dramatically bulging forehead.[4] However, aside from dentition and size, there are very few morphological differences between male and female beaked whales. [5]

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