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''Dimetrodon'' (; meaning "two measures of teeth") is an extinct genus of synapsid that lived during the Early Permian period, around 295–272 million years ago (Ma).〔(【引用サイトリンク】title=Dimetrodon )〕〔Huttenlocker, A. K., and E. Rega. 2012. The Paleobiology and Bone Microstructure of Pelycosauriangrade Synapsids. Pp. 90–119 in A. Chinsamy (ed.) Forerunners of Mammals: Radiation, Histology, Biology. Indiana University Press.〕 It is a member of the family Sphenacodontidae. The most prominent feature of ''Dimetrodon'' is the large sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the southwestern United States, the majority coming from a geological deposit called the Red Beds in Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first described in 1878. ''Dimetrodon'' is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it went extinct some 40 million years before the first appearance of dinosaurs. Reptile-like in appearance and physiology, ''Dimetrodon'' is nevertheless more closely related to mammals than to reptiles, though it is not a direct ancestor or descendant of mammals.〔 ''Dimetrodon'' is assigned to a group traditionally called "mammal-like reptiles"—more recently termed "stem-mammals" or "non-mammalian synapsids".〔 That is, many vertebrate paleontologists today group ''Dimetrodon'' together with mammals in an evolutionary group, or clade, called Synapsida, while they place dinosaurs with living reptiles and birds in a separate clade, Sauropsida. Temporal openings and other skull features distinguish ''Dimetrodon'' and mammals from most of the earliest sauropsids. ''Dimetrodon'' was probably one of the top predators in Early Permian ecosystems, feeding on fish and tetrapods, including reptiles as well as amphibians. Smaller ''Dimetrodon'' species may have had different ecological roles. The sail of ''Dimetrodon'' may have been used to stabilize its spine or to heat and cool its body as a form of thermoregulation. Some recent studies argue that the sail would have been ineffective at removing heat from the body, and was more likely used in sexual display. == Description == ''Dimetrodon'' was a quadrupedal, sail-backed synapsid. Most ''Dimetrodon'' species ranged in length from and are estimated to have weighed between . The largest known species of ''Dimetrodon'' is ''D. angelensis'' at and the smallest is ''D. teutonis'' at .〔(【引用サイトリンク】title=The Kungurian Age )〕 The larger species of ''Dimetrodon'' were among the largest predators of the Early Permian, although the closely related ''Tappenosaurus'', known from skeletal fragments in slightly younger rocks, may have been even larger at an estimated in total body length. 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「dimetrodon」の詳細全文を読む スポンサード リンク
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