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An eared seal or otariid or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera (another species became extinct in the 1950s) and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans and the southern Indian and Atlantic Oceans. They are conspicuously absent in the north Atlantic. The words 'otariid' and 'otary' come from the Greek ''otarion'' meaning "little ear",〔"Otary, n., etymology of" The Oxford English Dictionary. 2nd ed. 1989. OED Online. Oxford University Press. http://dictionary.oed.com/ Accessed November 2007〕 referring to the small but visible external ear flaps (pinnae), which distinguishes them from the phocids. ==Evolution and taxonomy== |2= }} |2= |3= }} |2= |2=Steller sea lion }} }} |2=northern fur seal }} |label2=Odobenidae |2= walrus }} }} }} |caption=Cladogram showing the eared seals, Otariidae, and their relationships with other pinnipeds, combining several phylogenetic analyses.〔 〕 }} Along with the Phocidae and Odobenidae, the two other members of Pinnipedia, Otаriidae are descended from a common ancestor most closely related to modern bears. Debate remains as to whether the phocids diverged from the otariids before or after the walrus. Otariids arose in the Miocene (15-17 million years ago) in the North Pacific, diversifying rapidly into the Southern Hemisphere, where most species now live. The earliest known fossil osariid is ''Eotaria crypta'' from southern California, while the genus ''Callorhinus'' (northern fur seal) has the oldest fossil record of any living otariid, extending to the middle Pliocene. It probably arose from the extinct fur seal genus ''Thalassoleon''. Traditionally, otariids had been subdivided into the fur seal (Arctocephalinae) and sea lion (Otariinae) subfamilies, with the major distinction between them being the presence of a thick underfur layer in the former. Under this categorization, the fur seals comprised two genera: ''Callorhinus'' in the North Pacific with a single representative, the northern fur seal (''C. ursinus''), and eight species in the Southern Hemisphere under the genus ''Arctocephalus''; while the sea lions comprise five species under five genera. Recent analyses of the genetic evidence suggests that ''Callorhinus ursinus'' is in fact more closely related to several sea lion species. Furthermore, many of the Otariinae appear to be more phylogenetically distinct than previously assumed; for example, the Japanese sea lion (''Zalophus japonicus'') is now considered a separate species, rather than a subspecies of the California sea lion (''Zalophus californius''). In light of this evidence, the subfamily separation has been removed entirely and the Otariidae family has been organized into seven genera with 16 species and two subspecies. Nonetheless, because of morphological and behavioral similarities among the "fur seals" and "sea lions", these remain useful categories when discussing differences between groups of species. Compared to sea lions, fur seals are generally smaller, exhibit greater sexual dimorphism, eat smaller prey and go on longer foraging trips; and, of course, there is the contrast between the coarse short sea lion hair and the fur seal's fur. 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「eared seal」の詳細全文を読む スポンサード リンク
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