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Cryptodira is a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira (side-neck turtles) in that they lower their necks and pull the heads straight back into the shells, instead of folding their necks sideways along the body under the shells' margins. They include among their species freshwater turtles, snapping turtles, tortoises, soft-shell turtles, and sea turtles. == Systematics and evolution == Cryptodires evolved during the Jurassic period, and by the end of the Jurassic had almost completely replaced pleurodires in the lakes and rivers, while beginning to develop land-based species. The Cryptodira suborder has three living superfamilies, the Chelonioidea (sea turtles), Testudinoidea (tortoises and pond turtles), and Trionychoidea (soft-shell turtles and relatives). The families within the Kinosternoidea are now recognized as a paraphyletic assemblage of mostly primitive Trionychoidea; they do not form a natural group.〔See references in Haaramo (2008)〕 Two circumscriptions of the Cryptodira are commonly found. One is used here; it includes a number of primitive extinct lineages known only from fossils, as well as the Eucryptodira. These are, in turn, made up from some very basal groups, and the Centrocryptodira contain the prehistoric relatives of the living cryptodires, as well as the latter, which are collectively called Polycryptodira.〔 The alternate concept restricts the use of the term "Cryptodira" to the crown clade (i.e. Polycryptodira). The Cryptodira as understood here are called Cryptodiramorpha in this view. Under this approach, the pleurodires and cryptodires are not sister taxa.〔 As per the system used here, the Cryptodira can be classified as: * †''Dracochelys'' * †''Emarginachelys'' * †''Hangaiemys'' * †''Judithemys'' * †''Mongolemys'' * †''Sinemys'' * †''Ordosemys'' * †Paracryptodira * * †''Dorsetochelys'' * * Family Baenidae * * Family Pleurosternidae * Family †"Plesiochelyidae" * Family †Xinjiangchelyidae * Clade Panchelonioidea * * Superfamily Chelonioidea (sea turtles) * * * Family †Protostegidae * * * Family †Thalassemydidae * * * Family †Toxochelyidae * * * Family Cheloniidae (green sea turtles and relatives) * * * Family Dermochelyidae (leatherback turtles) * Superfamily Testudinoidea * * Family †Haichemydidae * * Family †Lindholmemydidae * * Family †Sinochelyidae * * Family Platysternidae (big-headed turtle) * * Family Emydidae (pond, box and water turtles) * * Family Geoemydidae (Asian river turtles, Asian leaf turtles, Asian box turtles and roofed turtles) * * Family Testudinidae (tortoises) * Clade Panchelydridae * * Family Chelydridae (snapping turtles) * Superfamily Kinosternoidea * * Family Dermatemydidae (river turtles) * * Family Kinosternidae (mud turtles) * Clade Pantrionychia * * Genus †''Adocus'' * * Superfamily Trionychia * * * Family Carettochelyidae (pignose turtles) * * * Family Trionychidae (softshell turtles) 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「Cryptodira」の詳細全文を読む スポンサード リンク
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