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''Gorgosaurus'' ( ; meaning "dreadful lizard") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana. Paleontologists recognize only the type species, ''G. libratus'', although other species have been erroneously referred to the genus. Like most known tyrannosaurids, ''Gorgosaurus'' was a bipedal predator weighing more than two metric tons as an adult; dozens of large, sharp teeth lined its jaws, while its two-fingered forelimbs were comparatively small. ''Gorgosaurus'' was most closely related to ''Albertosaurus'', and more distantly related to the larger ''Tyrannosaurus''. ''Gorgosaurus'' and ''Albertosaurus'' are extremely similar, distinguished mainly by subtle differences in the teeth and skull bones. Some experts consider ''G. libratus'' to be a species of ''Albertosaurus''; this would make ''Gorgosaurus'' a junior synonym of that genus. ''Gorgosaurus'' lived in a lush floodplain environment along the edge of an inland sea. It was an apex predator, preying upon abundant ceratopsids and hadrosaurs. In some areas, ''Gorgosaurus'' coexisted with another tyrannosaurid, ''Daspletosaurus''. Although these animals were roughly the same size, there is some evidence of niche differentiation between the two. ''Gorgosaurus'' is the best-represented tyrannosaurid in the fossil record, known from dozens of specimens. These plentiful remains have allowed scientists to investigate its ontogeny, life history and other aspects of its biology. ==Description== ''Gorgosaurus'' was smaller than ''Tyrannosaurus'' or ''Tarbosaurus'', closer in size to ''Albertosaurus'' and ''Daspletosaurus''. Adults reached from snout to tail. Paleontologists have estimated full-grown adults to weigh more than , perhaps approaching . The largest known skull measures long, just slightly smaller than that of ''Daspletosaurus''.〔 As in other tyrannosaurids, the skull was large compared to its body size, although chambers within the skull bones and large openings (fenestrae) between bones reduced its weight. ''Albertosaurus'' and ''Gorgosaurus'' share proportionally longer and lower skulls than ''Daspletosaurus'' and other tyrannosaurids. The end of the snout was blunt, and the nasal and parietal bones were fused along the midline of the skull, as in all other members of the family. The eye socket was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera. A tall crest rose from the lacrimal bone in front of each eye, similar to ''Albertosaurus'' and ''Daspletosaurus''.〔 Differences in the shape of bones surrounding the brain set ''Gorgosaurus'' apart from ''Albertosaurus''. ''Gorgosaurus'' teeth were typical of all known tyrannosaurids. The eight premaxillary teeth at the front of the snout were smaller than the rest, closely packed and ''D''-shaped in cross section. In ''Gorgosaurus'', the first tooth in the maxilla was also shaped like the premaxillary teeth. The rest of the teeth were oval in cross section, rather than blade-like as in most other theropods.〔 Along with the eight premaxillary teeth, ''Gorgosaurus'' had 26 to 30 maxillary teeth and 30 to 34 teeth in the dentary bones of the lower jaw. This number of teeth is similar to ''Albertosaurus'' and ''Daspletosaurus'' but is fewer than those of ''Tarbosaurus'' or ''Tyrannosaurus''. ''Gorgosaurus'' shared its general body plan with all other tyrannosaurids. Its massive head was perched on the end of an ''S''-shaped neck. In contrast to its large head, its forelimbs were very small. The forelimbs had only two digits, although a third metacarpal is known in some specimens, the vestigial remains of the third digit seen in other theropods. ''Gorgosaurus'' had four digits on each hindlimb, including a small first toe (hallux) which did not contact the ground. Tyrannosaurid hindlimbs were long relative to overall body size compared with other theropods.〔 The largest known ''Gorgosaurus'' femur measured long. In several smaller specimens of ''Gorgosaurus'', the tibia was longer than the femur, a proportion typical of fast-running animals.〔 The two bones were of equal length in the largest specimens. The long, heavy tail served as a counterweight to the head and torso and placed the center of gravity over the hips.〔 In 2001, paleontologist Phil Currie reported skin impressions from the holotype specimen of ''G. libratus''. He originally reported the skin as being smooth and lacking the scales found in other dinosaurs; similar to the secondarily featherless skin found in large modern birds.〔Currie, P. (2001). 2001 A. Watson Armour Symposium: The Paleobiology and Phylogenetics of Large Theropods. Field Museum of Natural History, Chicago.〕 However, this original interpretation was found to be an exaggeration based on the relatively fine scalation of the ''Gorgosaurus'' skin impression (approximately as fine as a Gila monster's).〔Holtz, T. 2001. Phil Currie celebration, tyrant skin, and other things. Dinosaur Mailing List post. http://dml.cmnh.org/2001Jul/msg00243.html. Accessed: 15 March 2014〕 In the ''Encyclopedia of Dinosaurs'' Kenneth Carpenter pointed out that traces of skin impressions from the tail of ''Gorgosaurus'' showed similar small rounded or hexagonal scales. 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「Gorgosaurus」の詳細全文を読む スポンサード リンク
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