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''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been named, modern paleontologists recognize only one, ''T. bataar'', as valid. Some experts see this species as an Asian representative of the North American genus ''Tyrannosaurus''; this would make the genus ''Tarbosaurus'' redundant. ''Tarbosaurus'' and ''Tyrannosaurus'', if not synonymous, are considered to be at least closely related genera. ''Alioramus'', also from Mongolia, is thought by some authorities to be the closest relative of ''Tarbosaurus''. Like most known tyrannosaurids, ''Tarbosaurus'' was a large bipedal predator, weighing up to five tonnes and equipped with about sixty large teeth. It had a unique locking mechanism in its lower jaw and the smallest forelimbs relative to body size of all tyrannosaurids, renowned for their disproportionately tiny, two-fingered forelimbs. ''Tarbosaurus'' lived in a humid floodplain criss-crossed by river channels. In this environment, it was an apex predator at the top of the food chain, probably preying on other large dinosaurs like the hadrosaur ''Saurolophus'' or the sauropod ''Nemegtosaurus''. ''Tarbosaurus'' is represented by dozens of fossil specimens, including several complete skulls and skeletons. These remains have allowed scientific studies focusing on its phylogeny, skull mechanics, and brain structure. ==Description== Although smaller than ''Tyrannosaurus'', ''Tarbosaurus'' was one of the largest tyrannosaurids. The largest known individuals were between long. The mass of a fully grown individual is considered comparable to or slightly smaller than ''Tyrannosaurus'', often estimated to be around 4–5 metric tons.〔Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press.〕 The largest known ''Tarbosaurus'' skull is more than long, larger than all other tyrannosaurids except ''Tyrannosaurus''.〔 The skull was tall, like that of ''Tyrannosaurus'', but not as wide, especially towards the rear. The unexpanded rear of the skull meant that ''Tarbosaurus'' eyes did not face directly forwards, suggesting that it lacked the binocular vision of ''Tyrannosaurus''. Large fenestrae (openings) in the skull reduced its weight. Between 58 and 64 teeth lined its jaws, slightly more than in ''Tyrannosaurus'' but fewer than in smaller tyrannosaurids like ''Gorgosaurus'' and ''Alioramus''. Most of its teeth were oval in cross section, although the teeth of the premaxilla at the tip of the upper jaw had a ''D''-shaped cross section. This heterodonty is characteristic of the family. The longest teeth were in the maxilla (upper jaw bone), with crowns up to 85 millimeters (3.3 in) long. In the lower jaw, a ridge on the outer surface of the angular bone articulated with the rear of the dentary bone, creating a locking mechanism unique to ''Tarbosaurus'' and ''Alioramus''. Other tyrannosaurids lacked this ridge and had more flexibility in the lower jaw. Tyrannosaurids varied little in body form, and ''Tarbosaurus'' was no exception. The head was supported by an ''S''-shaped neck, while the rest of the vertebral column, including the long tail, was held horizontally. ''Tarbosaurus'' had tiny forelimbs, proportionably to body size the smallest of all members of the family. The hands had two clawed digits each, with an additional unclawed third metacarpal found in some specimens, similar to closely related genera. Holtz has suggested that ''Tarbosaurus'' also has a theropod reduction of fingers IV-I "developed further" than in other tyrannosaurids,〔Carpenter K, Tanke D.H. & Skrepnick M.W. (2001), ''Mesozoic Vertebrate Life'' (Indiana University Press, ISBN 0-253-33907-3), p. 71.〕 as the second metacarpal in the ''Tarbosaurus'' specimens he studied is less than twice the length of the first metacarpal (other tyrannosaurids have a second metacarpal about twice the length of the first metacarpal). Also, the third metacarpal in ''Tarbosaurus'' is proportionally shorter than in other tyrannosaurids; in other tyrannosaurids (like ''Albertosaurus'' and ''Daspletosaurus''), the third metacarpal is often longer than the first metacarpal, while in the ''Tarbosaurus'' specimens studied by Holtz, the third metacarpal is shorter than the first. In contrast to the forelimbs, the three-toed hindlimbs were long and thick, supporting the body in a bipedal posture. The long, heavy tail served as a counterweight to the head and torso and placed the center of gravity over the hips.〔〔 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「Tarbosaurus」の詳細全文を読む スポンサード リンク
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