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Diplodocids, or members of the family Diplodocidae ("double beams"), are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the Earth, including ''Diplodocus'', ''Supersaurus'', and now, ''Brontosaurus'', all of which may have reached lengths of up to .〔Tschopp, E., Mateus O., & Benson R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ. 3, e857., 4〕 ==Description== While still massive, when compared to the titanosaurids and brachiosaurs, the diplodocids were relatively slender but extremely long. They had short legs, making them the "dachshund" of giant dinosaurs; and their rear legs were longer than front legs, giving their back a distinctive downward slope towards the neck. In 1992, a fragmentary diplodocid specimen was described with associated keratinous (horny, not bony) spines. Their arrangement suggests that in life the spines formed a continuous line down the diplodocid's back. Since dermal tissue is rarely preserved in the fossil record it is not known how widespread the feature is, but spines may have been a common feature among diplodocids or among sauropods as a whole.〔Czerkas, S. A. (1992). Discovery of dermal spines reveals a new look for sauropod dinosaurs. Geology, 20(12), 1068-1070.〕 Their necks were also extremely long, and according to recent computer simulations they may not have been able to lift their necks like other sauropods. However these simulations do not take vertebral cartilage into account, which would likely allow a greater range of motion. Instead of reaching up into trees, they may have used their necks to graze over a broad area. They may also have used their necks to reach into dense stands of conifers, or over marshy ground. Their heads, like those of other sauropods, were tiny with the nasal openings on the top of the head (though in life the nostrils themselves would have been close to the tip of the snout). Their teeth were only present in the front of the mouth, and looked like pencils or pegs. They probably used their teeth to crop off food, without chewing, and relied on gastroliths (gizzard stones) to break down tough plant fibers (similar to modern birds). The heads of diplodocids have been widely depicted with the nostrils on top due to the position of the nasal openings at the apex of the skull. There has been speculation over whether such a configuration meant that diplodocids may have had a trunk.〔Bakker, Robert T. (1986) The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and their Extinction. New York: Morrow.〕 A 2006 study surmised there was no paleoneuroanatomical evidence for a trunk. It noted that the facial nerve in an animal with a trunk, such as an elephant, is large as it innervates the trunk. The evidence suggests that the facial nerve is very small in diplodocids. Studies by Lawrence Witmer (2001) indicated that, while the nasal openings were high on the head, the actual, fleshy nostrils were situated much lower down on the snout. Diplodocids also had long, whip-like tails, which were thick at the base and tapered off to be very thin at the end. Computer simulations have shown that the diplodocids could have easily snapped their tails, like a bullwhip. This could generate a sonic boom in excess of 200 decibels, and may have been used in mating displays, or to drive off predators. There is some circumstantial evidence supporting this as well: A number of diplodocids have been found with fused or damaged tail vertebrae, which may be a symptom of cracking their tails. 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「diplodocid」の詳細全文を読む スポンサード リンク
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