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Oceanic dolphins are a widely distributed family of fully aquatic marine mammals. The oceanic dolphins comprises the family Delphinidae. There are 30 extant species of oceanic dolphins. Dolphins, alongside other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates, and their closest living relatives are the hippopotamuses, having diverged about 40 million years ago. Oceanic dolphins range in size from the long and Maui's dolphin to the and killer whale, the largest known dolphin. Several species exhibit sexual dimorphism, in that the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can travel at . Most delphinids primarily eat fish, along with a smaller number of squid and small crustaceans, but some species specialise in eating squid, or, in the case of the killer whale, also eat marine mammals and birds. All, however, are purely carnivorous. They typically have between 100 and 200 teeth, although a few species have considerably fewer. Delphinids travel in large pods, which may number a thousand individuals in some species. Each pod forages over a range of a few dozen to a few hundred square miles. Some pods have a loose social structure, with individuals frequently joining or leaving, but others seem to be more permanent, perhaps dominated by a male and a harem of females.〔 Individuals communicate by sound, producing low-frequency whistles, and also produce high-frequency broadband clicks of 80-220 kHz, which are primarily used for echolocation. Gestation lasts from 10 to 18 months, and results in the birth of a single calf. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water. Although oceanic dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Some have a global distribution, like the killer whale. Oceanic dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks and whistles. Oceanic dolphins are sometimes hunted in places like Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they also face threats from bycatch, habitat loss, and marine pollution. Dolphins have been depicted in various cultures worldwide. They occasionally feature in literature and film, as in the Warner Bros film Free Willy. Oceanic dolphins are kept in captivity and trained to perform tricks, but breeding success has been poor and the animals often die within a few months of capture. The most common dolphins kept are the killer whales and bottlenose dolphins. == Taxonomy == Delphinids, especially bottlenose dolphins, are able to hybridize with a wide variety of other delphinid species; wolphins are just one of many possible hybrids. There are six species, sometimes referred to as "blackfish", that are dolphins commonly misconceived as whales: the killer whale, the melon-headed whale, the pygmy killer whale, the false killer whale, and the two species of pilot whales, but they are classified under the family Delphinidae. * ORDER CETARTIODACTYLA * * Infraorder Cetacea * * * Suborder Odontoceti * * * * Superfamily Delphinoidea * * * * * Family Delphinidae * * * * * * Genus ''Peponocephala'' * * * * * * * Melon-headed whale, ''Peponocephala electra'' * * * * * * Genus ''Orcinus'' * * * * * * * Killer whale (orca), ''Orcinus orca'' * * * * * * * ''Orcinus citoniensis'' † * * * * * * Genus ''Feresa'' * * * * * * * Pygmy killer whale, ''Feresa attenuata'' * * * * * * Genus ''Pseudorca'' * * * * * * * False killer whale, ''Pseudorca crassidens'' * * * * * * Genus ''Globicephala'' * * * * * * * Long-finned pilot whale, ''Globicephala melas'' * * * * * * * Short-finned pilot whale, ''Globicephala macrorhynchus'' * * * * * * Genus ''Delphinus'' * * * * * * * Long-beaked common dolphin, ''Delphinus capensis'' * * * * * * * Short-beaked common dolphin, ''Delphinus delphis'' * * * * * * Genus ''Lissodelphis'' * * * * * * * Northern right whale dolphin, ''Lissodelphis borealis'' * * * * * * * Southern right whale dolphin, ''Lissodelphis peronii'' * * * * * * Genus ''Sotalia'' * * * * * * * Tucuxi, ''Sotalia fluviatilis'' * * * * * * * Costero, ''Sotalia guianensis'' * * * * * * Genus ''Sousa'' * * * * * * * Pacific humpback dolphin, ''Sousa chinensis'' * * * * * * * Indian humpback dolphin, ''Sousa plumbea'' * * * * * * * Atlantic humpback dolphin, ''Sousa teuszii'' * * * * * * Genus ''Stenella'' * * * * * * * Atlantic spotted dolphin, ''Stenella frontalis'' * * * * * * * Clymene dolphin, ''Stenella clymene'' * * * * * * * Pantropical spotted dolphin, ''Stenella attenuata'' * * * * * * * Spinner dolphin, ''Stenella longirostris'' * * * * * * * Striped dolphin, ''Stenella coeruleoalba'' * * * * * * Genus ''Steno'' * * * * * * * Rough-toothed dolphin, ''Steno bredanensis'' * * * * * * Genus ''Tursiops'' * * * * * * * Common bottlenose dolphin, ''Tursiops truncatus'' * * * * * * * Indo-Pacific bottlenose dolphin, ''Tursiops aduncus'' * * * * * * * Burrunan dolphin, ''Tursiops australis'' * * * * * * Genus ''Cephalorhynchus'' * * * * * * * Chilean dolphin, ''Cephalorhynchus eutropia'' * * * * * * * Commerson's dolphin, ''Cephalorhynchus commersonii'' * * * * * * * Heaviside's dolphin, ''Cephalorhynchus heavisidii'' * * * * * * * Hector's dolphin, ''Cephalorhynchus hectori'' * * * * * * Genus ''Grampus'' * * * * * * * Risso's dolphin, ''Grampus griseus'' * * * * * * Genus ''Lagenodelphis'' * * * * * * * Fraser's dolphin, ''Lagenodelphis hosei'' * * * * * * Genus ''Lagenorhynchus'' * * * * * * * Atlantic white-sided dolphin, ''Lagenorhynchus acutus'' * * * * * * * Dusky dolphin, ''Lagenorhynchus obscurus'' * * * * * * * Hourglass dolphin, ''Lagenorhynchus cruciger'' * * * * * * * Pacific white-sided dolphin, ''Lagenorhynchus obliquidens'' * * * * * * * Peale's dolphin, ''Lagenorhynchus australis'' * * * * * * * White-beaked dolphin, ''Lagenorhynchus albirostris'' * * * * * * Genus ''Orcaella'' * * * * * * * Irrawaddy dolphin, ''Orcaella brevirostris'' * * * * * * * Australian snubfin dolphin, ''Orcaella heinsohni'' * * * * * * Genus †''Australodelphis'' * * * * * * * †''Australodelphis mirus'' * * * * * * Genus †''Etruridelphis'' * * * * * * * †''Etruridelphis giulii'' 〔Bianucci, G., Vaiani, S. C. & Casati, S. (2009): A new delphinid record (Odontoceti, Cetacea) from the Early Pliocene of Tuscany (Central Italy): systematics and biostratigraphic considerations. N. Jb. Geol. Paläont. Abh., 254: 275–292.〕 Recent molecular analyses indicate that several delphinid genera (especially ''Stenella'' and ''Lagenorhynchus'') are not monophyletic as currently recognized. Thus, significant taxonomic revisions within the family are likely. 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「oceanic dolphin」の詳細全文を読む スポンサード リンク
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