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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Acristavus ： ウィキペディア英語版 Acristavus ''Acristavus'' is a genus of saurolophine dinosaur. Fossils have been found from the Campanian Two Medicine Formation in Montana and Wahweap Formation in Utah, United States. The type species ''A. gagslarsoni'' was named in 2011. Unlike nearly all hadrosaurids except ''Edmontosaurus'', ''Acristavus'' lacked ornamentation on its skull. The discovery of ''Acristavus'' is paleontologically significant because it supports the position that the ancestor of all hadrosaurids did not possess cranial ornamentation, and that ornamentation was an adaptation that later arose interdependently in the subfamilies Saurolophinae and Lambeosaurinae. It is closely related to ''Brachylophosaurus'' and ''Maiasaura'', and was assigned to a new clade called Brachylophosaurini. ==Discovery and occurrence== The holotype specimen of ''Acristavus'', MOR 1155, was recovered at the Two Medicine Formation, in Teton County, Montana. The specimen was collected in 1999 by C. Riley Nelson in well-indurated tan colored calcareous sandstone that was deposited during the Campanian stage of the Cretaceous period, approximately 79 million years ago.〔Jinnah, Z.A., Roberts, E.M., Deino, A.L., Larsen, J.S., Link, P.K. and Fanning, C.M. (2009). New 40Ar-39Ar and detrital zircon U-Pb ages for the Upper Cretaceous Wahweap and Kaiparowits formations on the Kaiparowits Plateau, Utah: implications for regional correlation, provenance and biostratigraphy. Cretaceous Research 30, 287-299.〕 MOR 1155 consists of an almost complete skull with associated postcrania including eleven cervical vertebrae, three incomplete dorsal vertebrae, a proximal caudal vertebra, several dorsal ribs, the left humerus, the left ulna, the right sternal, the left pubis, the left femur, the left tibia, two left metatarsals, five left pedal phalanges and one right pedal phalanx. A second specimen UMNHVP 16607 assigned to ''Acristavus'' in 2011, was excavated from the Smokey Mountain Road locality in Middle Mudstone Member of the Wahweap Formation in Utah. It was collected by C. R. Nelson in 2000, in lithified, yellow sandstone believed to be from the same time period as the type specimen. UMNHVP 16607 consists of a partial articulated skull, including both lacrimals, a complete braincase, and a cervical vertebra. 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「Acristavus」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.