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Amphicoelias
''Amphicoelias'' (, meaning "biconcave", from the Greek αμφι, ''amphi'': "on both sides", and κοιλος, ''koilos'': "hollow, concave") is a genus of herbivorous sauropod dinosaur that is probably synonymous with the genus ''Diplodocus''. It includes what has sometimes been estimated to be the largest dinosaur specimen ever discovered, originally named "''A. fragillimus''". Based on surviving descriptions of a single fossil bone, scientists had over the years estimated ''A. fragillimus'' to have been the longest known animal at in length, with potentially a mass of up to 122.4 tonnes (135 short tons). However, because the only fossil remains were lost at some point after being studied and described in the 1870s, evidence survived only in drawings and field notes. More recent analysis of the surviving evidence, and the biological plausibility of such a large land animal, has suggested that the enormous size of this animal were over-estimates due partly to typographical errors in the original 1878 description.
==Description==
The type species of ''Amphicoelias'', ''A. altus'', was named by paleontologist Edward Drinker Cope in December 1877 (though not published until 1878) for an incomplete skeleton consisting of two vertebrae, a pubis (hip bone), and a femur (upper leg bone).〔Cope, E.D. (1878a). "On the Vertebrata of the Dakota Epoch of Colorado." ''Proceedings of the American Philosophical Society'', 17: 233–247.〕 Cope also named a second species, ''A. fragillimus'', in the same paper. However, all subsequent researchers have considered ''A. fragillimus'' to be a synonym of ''A. altus''.〔 Even by 1881 however, it was recognized that ''A. altus'' could not be distinguished from other genera, as the features described by Cope were misinterpreted and are widespread. In 1921, Osborn and Mook assigned additional bones to ''A. altus''—a scapula (shoulder blade), a coracoid (shoulder bone), an ulna (lower arm bone), and a tooth. Henry Fairfield Osborn and Charles Craig Mook noted the overall close similarity between ''Amphicoelias'' and ''Diplodocus'', as well as a few key differences, such as proportionally longer forelimbs in ''Amphicoelias'' than in ''Diplodocus''. The dentition of ''Amphicoelias'' is homodont. Its teeth are shaped like long slender cylindrical rods, are spaced apart and project forward towards the front of the mouth. The femur of ''Amphicoelias'' is unusually long, slender, and round in cross section; while this roundness was once thought to be another distinguishing characteristic of ''Amphicoelias'', it has since been found in some specimens of ''Diplodocus'' as well.〔 ''A. altus'' was also similar in size to ''Diplodocus'', estimated to be about long and height.〔 While most scientists have used these details to distinguish ''Amphicoelias'' and ''Diplodocus'' as separate genera, at least one has suggested that ''Amphicoelias'' is probably the senior synonym of ''Diplodocus''.〔Foster, J. (2007). ''Jurassic West: The Dinosaurs of the Morrison Formation and Their World''. Indiana University Press.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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