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Turtles are reptiles of the order Testudines (or Chelonii) characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield. "Turtle" may refer to the order as a whole (American English) or to fresh-water and sea-dwelling testudines (British English). The order Testudines includes both extant (living) and extinct species. The earliest known members of this group date from , making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians. Of the 327 known species alive today, some are highly endangered.〔〔(Herpetology: An Introductory Biology of Amphibians and Reptiles )〕 Turtles are ectotherms—their internal temperature varies according to the ambient environment, commonly called cold-blooded. However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water. Turtles are classified as amniotes, along with other reptiles, birds, and mammals. Like other amniotes, turtles breathe air and do not lay eggs underwater, although many species live in or around water. ==Turtle, tortoise, or terrapin== The word ''chelonian'' is popular among veterinarians, scientists, and conservationists working with these animals as a catch-all name for any member of the superorder Chelonia, which includes all turtles living and extinct, as well as their immediate ancestors. ''Chelonia'' is based on the Greek word ''chelone'' "tortoise", "turtle" (another relevant word is ''chelys'' "tortoise"),〔, .〕 also denoting armor or interlocking shields; ''testudines'' on the other hand, is based on the Latin word ''testudo'' "tortoise". "Turtle" may either refer to the order as a whole, or to particular turtles that make up a form taxon that is not monophyletic. The meaning of the word ''turtle'' differs from region to region. In North America, all chelonians are commonly called turtles, including terrapins and tortoises. In Great Britain, the word ''turtle'' is used for sea-dwelling species, but not for tortoises. The term ''tortoise'' usually refers to any land-dwelling, non-swimming chelonian.〔 Most land-dwelling chelonians are in the Testudinidae family, only one of the 14 extant turtle families. ''Terrapin'' is used to describe several species of small, edible, hard-shell turtles, typically those found in brackish waters, and is an Algonquian word for turtle.〔 Some languages do not have this distinction, as all of these are referred to by the same name. For example, in Spanish, the word ''tortuga'' is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is ''tortuga marina'', a freshwater species ''tortuga de río'', and a tortoise ''tortuga terrestre''.〔''()'', Diccionario de la Real Academia Española〕 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「turtle」の詳細全文を読む スポンサード リンク
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