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Size has been one of the most interesting aspects of dinosaur science to the general public and to scientists. Dinosaurs show some of the most extreme variations in size of any land animal group, ranging from the tiny hummingbirds, which can weigh as little as three grams, to the extinct titanosaurs, which could weigh as much as 70 tonnes. Scientists will probably never be certain of the largest and smallest dinosaurs to have ever existed. This is because only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork. Weight estimates for dinosaurs are much more variable than length estimates, because estimating length for extinct animals is much more easily done from a skeleton than estimating weight. Estimating weight is most easily done with the laser scan skeleton technique that puts a "virtual" skin over it, but even this is only an estimate.〔Strauss, Bob."Why Were Dinosaurs So Big? The Facts and Theories Behind Dinosaur Gigantism". About Education. http://dinosaurs.about.com/od/dinosaurevolution/a/bigdinos.htm〕 Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods. Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the 100 to 1000 kilogram (220 to 2200 lb) category when sorted by estimated weight into categories based on order of magnitude, whereas recent predatory carnivoran mammals peak in the 10 to 100 kilogram (22 to 220 lb) category. The mode of Mesozoic dinosaur body masses is between one and ten metric tonnes. This contrasts sharply with the size of Cenozoic mammals, estimated by the National Museum of Natural History as about 2 to 5 kilograms (5 to 10 lb).〔(【引用サイトリンク】title=Anatomy and evolution )〕 ==Record sizes== The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as ''Paraceratherium'' (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales surpass them in size. There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.〔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.〕 One of the tallest and heaviest dinosaurs known from good skeletons is ''Giraffatitan brancai'' (previously classified as a species of ''Brachiosaurus''). Its remains were discovered in Tanzania between 1907 and 1912. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the Museum für Naturkunde Berlin;〔〕 this mount is tall and long, and would have belonged to an animal that weighed between and kilograms ( and lb). One of the longest complete dinosaurs is the 27-meter (89 ft) long ''Diplodocus'', which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Natural History Museum in 1907. There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were discovered in the 1970s or later, and include the massive titanosaur ''Argentinosaurus huinculensis'', which is the largest dinosaur known from uncontroversial evidence, estimated to have been over 〔 and long.〔 Some of the longest sauropods were those with exceptionally long, whip-like tails, such as the long ''Diplodocus hallorum''〔 (formerly ''Seismosaurus'') and the long ''Supersaurus'';〔 The tallest was the tall ''Sauroposeidon''. ''Tyrannosaurus'' was for many decades the largest theropod and best-known to the general public. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including ''Spinosaurus'', ''Carcharodontosaurus'', and ''Giganotosaurus''. The original ''Spinosaurus'' specimens (as well as newer fossils described in 2006) support the idea that ''Spinosaurus'' is larger than ''Tyrannosaurus'', showing that ''Spinosaurus'' was possibly 6 meters longer and at least 1 metric ton heavier than ''Tyrannosaurus''. ''Therizinosaurus'' and ''Deinocheirus'' were among the tallest of the theropods. There is still no clear explanation for exactly why these animals grew so much larger than the land predators that came before and after them. The largest extant theropod is the common ostrich, up to 2.74 m (9 ft) tall and weighs between 63.5 and 145.15 kg (140 - 320 lb).〔http://www.awf.org/wildlife-conservation/ostrich〕 The smallest non-avialan theropod known from adult specimens may be ''Anchiornis huxleyi'', at 110 grams in weight and 34 centimeters (1 ft) in length.〔Xu, X., Zhao, Q., Norell, M., Sullivan, C., Hone, D., Erickson, G., Wang, X., Han, F. and Guo, Y. (2009). "A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin." ''Chinese Science Bulletin'', 6 pages, accepted November 15, 2008.〕 However, some studies suggest that ''Anchiornis'' was actually an avialan. The smallest dinosaur known from adult specimens which is definitely not an avialan is ''Parvicursor remotus'', at and measuring long.〔(Which was the smallest dinosaur? ) Royal Tyrrell Museum. Last accessed 2008-05-23.〕 When modern birds are included, the bee hummingbird ''Mellisuga helenae'' is smallest at 1.9 g and 5.5 cm (2.2 in) long.〔Conservation International (Content Partner); Mark McGinley (Topic Editor). 2008. "Biological diversity in the Caribbean Islands." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). (published in the Encyclopedia of Earth May 3, 2007; Last revised August 22, 2008; Retrieved November 9, 2009 ). Recent theories propose that theropod body size shrank continuously over the past 50 million years, from an average of down to , eventually evolving into modern birds. This was based on evidence that theropods were the only dinosaurs to get continuously smaller, and that their skeletons changed four times faster than those of other dinosaur species.〔 〕 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「dinosaur size」の詳細全文を読む スポンサード リンク
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