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''Tyrannosaurus'' ( or ("tyrant lizard", from the Ancient Greek ''tyrannos'' (τύραννος), "tyrant", and ''sauros'' (σαῦρος), "lizard"〔(【引用サイトリンク】publisher=Online Etymology Dictionary )〕)) is a genus of coelurosaurian theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), commonly abbreviated to ''T. rex'', is one of the most well-represented of the large theropods. ''Tyrannosaurus'' lived throughout what is now western North America, on what was then an island continent known as Laramidia. ''Tyrannosaurus'' had a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 68 to 66 million years ago. It was the last known member of the tyrannosaurids, and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event. Like other tyrannosaurids, ''Tyrannosaurus'' was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, ''Tyrannosaurus'' fore limbs were short but unusually powerful for their size and had two clawed digits. The most complete specimen measures up to in length,〔 up to tall at the hips, and up to in weight. Although other theropods rivaled or exceeded ''Tyrannosaurus rex'' in size, it is still among the largest known land predators and may have exerted one of the largest biting forces among all animals, given its skull structure.〔〔 By far the largest carnivore in its environment, ''Tyrannosaurus rex'' may have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods, although some experts have suggested the dinosaur was primarily a scavenger. The question of whether ''Tyrannosaurus'' was an apex predator or a pure scavenger was among the longest ongoing debates in paleontology; however, a majority of scientists now agree that ''Tyrannosaurus rex'' was most likely an opportunistic carnivore, acting as both a predator and a scavenger when appropriate. More than 50 specimens of ''Tyrannosaurus rex'' have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including its life history and biomechanics. The feeding habits, physiology and potential speed of ''Tyrannosaurus rex'' are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider ''Tarbosaurus bataar'' from Asia to be a second ''Tyrannosaurus'' species while others maintain ''Tarbosaurus'' is a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with ''Tyrannosaurus''. ==Description== ''Tyrannosaurus rex'' was one of the largest land carnivores of all time; the largest complete specimen, located at the Field Museum of Natural History under the name FMNH PR2081 and nicknamed Sue, measured long, and was tall at the hips.〔 Mass estimates have varied widely over the years, from more than , to less than , with most modern estimates ranging between and .〔 One study in 2011 found that the maximum weight of Sue, the largest ''Tyrannosaurus'', was between , though the authors stated that their upper and lower estimates were based on models with wide error bars and that they "consider () to be too skinny, too fat, or too disproportionate".〔 Packard ''et al.'' (2009) tested dinosaur mass estimation procedures on elephants and concluded that those of dinosaurs are flawed and produce over-estimations; thus, the weight of ''Tyrannosaurus'' could have been much less than previously thought. Other estimations have concluded that the largest known ''Tyrannosaurus'' specimens had masses approaching or exceeding 9 tonnes.〔〔http://dinoweb.ucoz.ru/_fr/4/My_theropod_is_.pdf〕 The neck of ''Tyrannosaurus rex'' formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs had only two clawed fingers,〔 along with an additional small metacarpal representing the remnant of a third digit. In contrast the hind limbs were among the longest in proportion to body size of any theropod. The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the massive head and torso. To compensate for the immense bulk of the animal, many bones throughout the skeleton were hollow, reducing its weight without significant loss of strength.〔 The largest known ''Tyrannosaurus rex'' skulls measure up to in length. Large fenestrae (openings) in the skull reduced weight and provided areas for muscle attachment, as in all carnivorous theropods. But in other respects ''Tyrannosaurus'' The teeth of ''Tyrannosaurus rex'' displayed marked heterodonty (differences in shape). The premaxillary teeth at the front of the upper jaw were closely packed, ''D''-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards. The ''D''-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when ''Tyrannosaurus'' bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers, more widely spaced and also had reinforcing ridges. Those in the upper jaw were larger than those in all but the rear of the lower jaw. The largest found so far is estimated to have been long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found.〔 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「Tyrannosaurus」の詳細全文を読む スポンサード リンク
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