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Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines. There are seven species of sea turtles. They are the leatherback sea turtle, green sea turtle, loggerhead sea turtle, Kemp's ridley sea turtle, hawksbill sea turtle, flatback sea turtle and olive ridley sea turtle. Four of the species have been identified as "endangered" or "critically endangered" with another two being classed as "vulnerable". ==Taxonomy and evolution== The origin of Sea Turtles goes back to the Late Jurassic (150 Ma) with genera such as ''Plesiochelys'', from Europe. In Africa, the first marine turtle is ''Angolachelys'', from the Turonian of Angola. The difference between a sea turtle and other turtles is that their legs and arms cannot retract back into their shells.〔(【引用サイトリンク】url=http://www.defenders.org/sea-turtles/basic-facts )〕 Sea turtles, along with other turtles and tortoises, are part of the order Testudines. The seven living species of sea turtles are: leatherback sea turtle, green sea turtle, loggerhead sea turtle, Kemp's ridley sea turtle, hawksbill sea turtle, flatback sea turtle and olive ridley sea turtle.〔The East Pacific sub-population of the green turtle was previously classified as a separate species, the black sea turtle, but DNA evidence indicates that it is not evolutionarily distinct from the green sea turtle.〕 All species except the leatherback are in the family Cheloniidae. The leatherback belongs to the family Dermochelyidae and is its only extant member. The species are primarily distinguished by their anatomy: for instance, the prefrontal scales on the head, the number of and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron. The leatherback is the only sea turtle that does not have a hard shell; instead, it bears a mosaic of bony plates beneath its leathery skin. It is the largest sea turtle, measuring in length at maturity, and in width, weighing up to . Other species are smaller, being mostly and proportionally narrower.〔(【引用サイトリンク】url=http://www.turtlehospital.org/sea-turtle-species/ )〕 Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago. * Family Cheloniidae * * ''Chelonia mydas'', green sea turtle * * ''Caretta caretta'', loggerhead sea turtle * * ''Lepidochelys kempii'', Kemp's ridley sea turtle * * ''Eretmochelys imbricata'', hawksbill sea turtle * * ''Natator depressus'', flatback sea turtle * * ''Lepidochelys olivacea'', olive ridley sea turtle * Family Dermochelyidae * * ''Dermochelys coriacea'', leatherback sea turtle File:LeatherbackTurtle.jpg|Leatherback sea turtle (''Dermochelys coriacea'') File:Green turtle swimming over coral reefs in Kona.jpg|Green sea turtle (''Chelonia mydas'') File:Loggerhead sea turtle.jpg|Loggerhead sea turtle (''Caretta caretta'') File:Hawksbill Turtle.jpg|Hawksbill sea turtle (''Eretmochelys imbricata'') File:Natator depressus.jpg|Flatback sea turtle (''Natator depressus'') File:Padre Island National Seashore - Kemps Ridley Sea Turtle.jpg|Kemp's ridley sea turtle (''Lepidochelys kempii'') File:Lepidochelys olivacea.jpg|Olive ridley sea turtle (''Lepidochelys olivacea'') 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「Sea turtle」の詳細全文を読む スポンサード リンク
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