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| synonyms = }} ''Allosaurus'' is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period (Kimmeridgian to early Tithonian〔Turner, C.E. and Peterson, F., (1999). "Biostratigraphy of dinosaurs in the Upper Jurassic Morrison Formation of the Western Interior, U.S.A." Pp. 77–114 in Gillette, D.D. (ed.), ''Vertebrate Paleontology in Utah''. Utah Geological Survey Miscellaneous Publication 99-1.〕). The name "''Allosaurus"'' means "different lizard". It is derived from the Greek /''allos'' ("different, other") and /''sauros'' ("lizard / generic reptile"). The first fossil remains that can definitely be ascribed to this genus were described in 1877 by paleontologist Othniel Charles Marsh, and it became known as ''Antrodemus''. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles. Indeed, it has been a top feature in several films and documentaries about prehistoric life. ''Allosaurus'' was a large bipedal predator. Its skull was large and equipped with dozens of sharp, serrated teeth. It averaged in length, though fragmentary remains suggest it could have reached over . Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long and heavily muscled tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is ''A. fragilis''. The bulk of ''Allosaurus'' remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as ''Antrodemus'', but study of the copious remains from the Cleveland-Lloyd Dinosaur Quarry brought the name "''Allosaurus"'' back to prominence, and established it as one of the best-known dinosaurs. As the most abundant large predator in the Morrison Formation, ''Allosaurus'' was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs and perhaps even other predators. Potential prey included ornithopods, stegosaurids, and sauropods. Some paleontologists interpret ''Allosaurus'' as having had cooperative social behavior, and hunting in packs, while others believe individuals may have been aggressive toward each other, and that congregations of this genus are the result of lone individuals feeding on the same carcasses. It may have attacked large prey by ambush, using its upper jaw like a hatchet. ==Description== ''Allosaurus'' was a typical large theropod, having a massive skull on a short neck, a long tail and reduced forelimbs. ''Allosaurus fragilis'', the best-known species, had an average length of , with the largest definitive ''Allosaurus'' specimen (AMNH 680) estimated at 9.7 meters long (32 ft), and an estimated weight of 2.3 metric tons (2.5 short tons).〔 In his 1976 monograph on ''Allosaurus'', James Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of . As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between , , and for modal adult weight (not maximum). John Foster, a specialist on the Morrison Formation, suggests that is reasonable for large adults of ''A. fragilis'', but that is a closer estimate for individuals represented by the average-sized thigh bones he has measured. Using the subadult specimen nicknamed "Big Al", researchers using computer modelling arrived at a best estimate of for the individual, but by varying parameters they found a range from approximately to approximately . Several gigantic specimens have been attributed to ''Allosaurus'', but may in fact belong to other genera. The closely related genus ''Saurophaganax'' (OMNH 1708) reached perhaps in length,〔 and its single species has sometimes been included in the genus ''Allosaurus'' as ''Allosaurus maximus'', though recent studies support it as a separate genus. Another potential specimen of ''Allosaurus'', once assigned to the genus ''Epanterias'' (AMNH 5767), may have measured 12.1 meters in length (40 ft).〔 A more recent discovery is a partial skeleton from the Peterson Quarry in Morrison rocks of New Mexico; this large allosaurid may be another individual of ''Saurophaganax''.〔Foster, John. 2007. ''Jurassic West: the Dinosaurs of the Morrison Formation and Their World.'' Bloomington, Indiana:Indiana University Press. p. 117.〕 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「allosaurus」の詳細全文を読む スポンサード リンク
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