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''Utahraptor'' (meaning "Utah's plunderer"〔) is a genus of theropod dinosaurs. It contains a single species, ''Utahraptor ostrommaysorum'', which is the largest known member of the family Dromaeosauridae. Fossil specimens date to the upper Barremian stage of the early Cretaceous period (in rock strata dated to 126 ± 2.5 million years ago).〔Kirkland, J.I. and Madsen, S.K. (2007). "The Lower Cretaceous Cedar Mountain Formation, eastern Utah: the view up an always interesting learning curve." ''Fieldtrip Guidebook, Geological Society of America, Rocky Mountain Section''. 1-108 p.〕 ==Description== The holotype specimen of ''Utahraptor'' is fragmentary, consisting of skull fragments, a tibia, claws and some caudal (tail) vertebrae. These few elements suggest an animal about twice the length of ''Deinonychus''.〔 Like other dromaeosaurids, ''Utahraptor'' had large curved claws on their second toes. One claw specimen is preserved at in length and is thought to reach restored. The largest described ''U. ostrommaysorum'' specimens are estimated to have reached up to long and somewhat less than in weight, comparable to a polar bear in size.〔〔Holtz, Thomas R. Jr. (2008) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages'' (Supplementary Information )〕 It is thought that ''Utahraptor'' may be closely related to the smaller ''Dromaeosaurus'' and the giant Mongolian dromaeosaurid genus ''Achillobator''.〔 Although feathers have never been found in association with ''Utahraptor'' specimens, there is strong phylogenetic evidence suggesting that all dromaeosaurids possessed them. This evidence comes from phylogenetic bracketing, which allows paleontologists to infer traits that exist in a clade based on the existence of that trait in a more basal form. The genus ''Microraptor'' is one of the oldest known dromaeosaurids, and is phylogenetically more primitive than ''Utahraptor''. Since ''Microraptor'' and other dromaeosaurids possessed feathers, it is reasonable to assume that this trait was present in all of Dromaeosauridae. Feathers were very unlikely to have evolved more than once, so assuming that any given dromaeosaurid, such as ''Utahraptor'', lacked feathers would require positive evidence that they did not have them. So far, there is nothing to suggest that feathers were lost in larger, more derived species of dromaeosaurs. In a 2001 study conducted by Bruce Rothschild and other paleontologists, two foot bones referred to ''Utahraptor'' were examined for signs of stress fracture, but none were found.〔Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.〕 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「Utahraptor」の詳細全文を読む スポンサード リンク
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