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Beaked whales are the members of the family Ziphiidae which consists of 22 species. These toothed whales are notable for their elongated beaks. Among air-breathing animals, beaked whales are some of the most extreme divers: Cuvier's beaked whales regularly dive for an hour at a depth over ,〔〕 and the longest and deepest foraging dive recorded is 137.5 minutes and . This is the greatest dive-depth known for a mammal. Beaked whales are one of the least known groups of mammals because of their deep-sea habitat, mysterious habits, and apparent low abundance.〔〕 Only three to four of the 22 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. ==Physical characteristics== Beaked whales are moderate in size, ranging from and weighing from . 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. However, aside from dentition and size, there are very few morphological differences between male and female beaked whales.〔〕 Individual species are very difficult to identify in the wild, since body form varies little from one species to another. The observer must rely on often subtle differences in size, color, forehead shape, and beak length. The blubber of these whales are almost entirely (94%) wax ester, a unique characteristic of this family.〔〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「beaked whale」の詳細全文を読む スポンサード リンク
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