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''Diplodocus'' (, ,〔 or 〔) is an extinct genus of diplodocid sauropod dinosaurs whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a neo-Latin term derived from Greek (unicode:διπλός) (''diplos'') "double" and (unicode:δοκός) (dokos) "beam",〔〔(【引用サイトリンク】url=http://www.etymonline.com/index.php?term=diplodocus&allowed_in_frame=0 )〕 in reference to its double-beamed chevron bones located in the underside of the tail. Chevron bones of this particular form were initially believed to be unique to ''Diplodocus''; however, since then they have been discovered in other members of the diplodocid family as well as in nondiplodocid sauropods, such as ''Mamenchisaurus''. It is now common scientific opinion that ''Seismosaurus hallorum'' is a species of ''Diplodocus''. This genus of dinosaurs lived in what is now western North America at the end of the Jurassic period. ''Diplodocus'' is one of the more common dinosaur fossils found in the middle to upper Morrison Formation, between about 154 and 152 million years ago, during the late Kimmeridgian age.〔 The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such as ''Apatosaurus'', ''Barosaurus'', ''Brachiosaurus'', ''Brontosaurus'', and ''Camarasaurus''. ''Diplodocus'' is among the most easily identifiable dinosaurs, with its typical sauropod shape, long neck and tail, and four sturdy legs. For many years, it was the longest dinosaur known. Its great size may have been a deterrent to the predators ''Allosaurus'' and ''Ceratosaurus'': their remains have been found in the same strata, which suggests that they coexisted with ''Diplodocus''. ==Description== One of the best-known sauropods, ''Diplodocus'' was a very large, long-necked, quadrupedal animal, with a long, whip-like tail. Its fore limbs were slightly shorter than its hind limbs, resulting in a largely horizontal posture. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge. In fact, ''Diplodocus'' is the longest dinosaur known from a complete skeleton.〔 The partial remains of ''D. hallorum'' have increased the estimated length, though not as much as previously thought; when first described in 1991, discoverer David Gillette calculated it may have been up to 54 m (177 ft) long,〔 making it the longest known dinosaur (excluding those known from exceedingly poor remains, such as ''Amphicoelias''). Some weight estimates ranged as high as 113 tons (125 US short tons). The estimated length was later revised downward to 〔Carpenter, K. (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod ''Amphicoelias fragillimus''." In Foster, J.R. and Lucas, S.G., eds., 2006, ''Paleontology and Geology of the Upper Jurassic Morrison Formation.'' New Mexico Museum of Natural History and Science Bulletin 36: 131–138.〕 based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. The nearly complete ''Diplodocus'' skeleton at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, on which estimates of ''Seismosaurus'' are based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing size estimates for ''Seismosaurus'' further off. While dinosaurs such as ''Supersaurus'' were probably longer, fossil remains of these animals are only fragmentary.〔Wedel, M.J. and Cifelli, R.L. ''Sauroposeidon'': Oklahoma's Native Giant. 2005. Oklahoma Geology Notes 65:2.〕 Modern mass estimates for ''Diplodocus'' (exclusive of ''D. hallorum'') have tended to be in the 10- to 16-tonne (11– to 17.6-ton) range: 10 tonnes (11 tons); 11.5 tonnes (12.7 tons);〔Paul, G.S. (1994). Big sauropods – really, really big sauropods. ''The Dinosaur Report, The Dinosaur Society'' Fall:12–13.〕 12.7 tonnes (14 tons);〔Foster, J.R. (2003). Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. New Mexico Museum of Natural History and Science:Albuquerque, New Mexico. Bulletin 23.〕 and 16 tonnes (17.6 tons). ''Diplodocus'' had an extremely long tail, composed of about 80 caudal vertebrae, which are almost double the number some of the earlier sauropods had in their tails (such as ''Shunosaurus'' with 43), and far more than contemporaneous macronarians had (such as ''Camarasaurus'' with 53). Some speculation exists as to whether it may have had a defensive〔 〕 or noisemaking (by cracking it like a coachwhip) function. The tail may have served as a counterbalance for the neck. The middle part of the tail had 'double beams' (oddly shaped chevron bones on the underside, which gave ''Diplodocus'' its name). They may have provided support for the vertebrae, or perhaps prevented the blood vessels from being crushed if the animal's heavy tail pressed against the ground. These 'double beams' are also seen in some related dinosaurs. No skull has ever been found that can be confidently said to belong to ''Diplodocus'', though skulls of other diplodocids closely related to ''Diplodocus'' (such as ''Galeamopus'') are well known. The skulls of diplodocids were very small compared with the size of these animals. ''Diplodocus'' had small, 'peg'-like teeth that pointed forward and were only present in the anterior sections of the jaws.〔 Its braincase was small. The neck was composed of at least 15 vertebrae and may have been held parallel to the ground and unable to be elevated much past horizontal. Like other sauropods, the manus (front "feet") of ''Diplodocus'' were highly modified, with the finger and hand bones arranged into a vertical column, horseshoe-shaped in cross section. ''Diplodocus'' lacked claws on all but one digit of the front limb, and this claw was unusually large relative to other sauropods, flattened from side to side, and detached from the bones of the hand. The function of this unusually specialized claw is unknown. Recent discoveries have suggested that ''Diplodocus'' and other diplodocids may have had narrow, pointed keratinous spines lining their back, much like those on an iguana.〔Czerkas, S. A. (1993). "Discovery of dermal spines reveals a new look for sauropod dinosaurs." Geology 20, 1068–1070〕〔Czerkas, S. A. (1994). "The history and interpretation of sauropod skin impressions." In ''Aspects of Sauropod Paleobiology'' (M. G. Lockley, V. F. dos Santos, C. A. Meyer, and A. P. Hunt, Eds.), ''Gaia'' No. 10. (Lisbon, Portugal).〕 This radically different look has been incorporated into recent reconstructions, notably ''Walking with Dinosaurs''. How many diplodocids had this trait is unknown exactly.〔Haines, T., James, J. ''(Time of the Titans )''. ABC Online.〕 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「Diplodocus」の詳細全文を読む スポンサード リンク
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