|
The cetacean family Monodontidae comprises two unusual whale species, the narwhal, in which the male has a long tusk, and the dorsal fin-lacking, pure white beluga whale. They are native to coastal regions and pack ice around the Arctic Sea. Belugas can be found in the far north of the Atlantic and Pacific Oceans; the distribution of narwhals is restricted to the Arctic and Atlantic Oceans. Both species are medium-sized whales, between three and five metres in length, with a forehead melon, and a short or absent snout. They do not have a true dorsal fin, but do have a narrow ridge running along the back, which is much more pronounced in the narwhal. They are highly vocal animals, communicating with a wide range of sounds. Like other whales, they also use echolocation to navigate. Monodontids have a wide-ranging carnivorous diet, feeding on fish, molluscs, and small crustaceans. They have reduced teeth, with the beluga having numerous simple teeth, and the narwhal having only two teeth, one of which forms the tusks in males. Gestation lasts 14-15 months in both species, and almost always results in a single calf. The young are not weaned for a full two years, and do not reach sexual maturity until they are five to eight years of age. Family groups travel as part of herds, or 'pods', which may contain several hundred individuals.〔 ==Taxonomy== The monodontids, dolphins (Delphinidae) and porpoises (Phocoenidae) together comprise the Delphinoidea superfamily. Genetic evidence suggests the porpoises are more closely related to the white whales, and these two families constitute a separate clade which diverged from the Delphinoidea within the past 11 million years. Suborder Odontoceti *Superfamily Delphinoidea * *Family Monodontidae * * *Subfamily Delphinapterinae * * * *Genus ''Delphinapterus'' * * * * *''Delphinapterus leucas'', beluga * * * *Genus † ''Denebola'' * * * * *''Denebola brachycephala'' * * *Subfamily Monodontinae * * * *Genus ''Monodon'' * * * * *''Monodon monoceros'', narwhal 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「Monodontidae」の詳細全文を読む スポンサード リンク
|