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''Brachylophosaurus'' ( or ; meaning "short-crested lizard", Greek ''brachys'' = short + ''lophos'' = crest + ''sauros'' = lizard, referring to its small crest) was a mid-sized member of the hadrosaurid family of dinosaurs. It is known from several skeletons and bonebed material from the Judith River Formation of Montana and the Oldman Formation of Alberta, living about 78 million years ago.〔 ==Description== ''Brachylophosaurus'' is notable for its bony crest, which forms a horizontally flat, paddle-like plate over the top of the rear skull.〔"Brachylophosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. ''The Age of Dinosaurs''. Publications International, LTD. p. 134. ISBN 0-7853-0443-6.〕 Some individuals, depending on their age, had crests that covered nearly the entire skull roof, while others had shorter, narrower crests. Some researchers have suggested it was used for pushing contests, but it may not have been strong enough for this. Other notable features are the unusually long forelimbs and the beak of the upper jaw being wider than other contemporary hadrosaurs.〔 Apart from the above, ''Brachylophosaurus'' was a typical hadrosaur which reached an adult length of nine meters (30 ft).〔 Like other hadrosaurs, ''Brachylophosaurus'' possessed features like cheeks to keep fodder in the mouth and dental batteries consisting of hundreds of teeth.〔 These teeth could be used to chew efficiently,〔 a feature rare among reptiles, but common among some cerapodan ornithischian dinosaurs like ''Brachylophosaurus''. In 2015, Jack Horner established some distinguishing traits. Two of these are autapomorphies, unique derived characters. The crest formed by the nasal bones is flat and paddle-shaped in adult individuals and largely or totally overhangs the supratemporal fenestrae. The rear edge of the prefrontal bone overgrowths the frontal bone and more to the rear is oriented inwards and downwards to support the base of the crest and contribute to the edge of the supratemporal fenestra. Additionally, there is one trait that is not unique in itself but forms a unique combination with the two autapomorphies: the front branch of the lacrimal bone is extremely elongated and with its tip only touches the maxillary bone.〔(Fowler, Elizabeth A. Freedman, and John R. Horner. "A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana." ''PloS one'' 10.11 (2015): e0141304. )〕 The head is elongated. It is wide at the rear and very narrow along most of the length of the snout. The upper beak however, abruptly widens at its rear edge, forming a broad bone core for a horn sheath. The nostrils are extremely large and between them the nasal bones form a narrow tall bone wall on top of much of the snout. More to behind the nasal bones stretch out horizontally, creating a flat tongue-shaped skull crest that overgrowths and ultimately overhangs, most of the skull roof. The crest is not hollow but consists of massive bone. The crest has a low longitudinal ridge on the midline. The maxilla, the tooth-bearing upper jaw bone, is rather elongated in front. Its tooth positions increase during the lifetime of the animal, ranging from thirty-three in younger individuals to forty-eight in the holotype specimen. The teeth are stacked in a tooth battery, with up to three teeth per position. The battery forms a sharp cutting edge, bending inwards, with one or sometimes two teeth per position contributing to the attrition surface. More to behind, the lower jugal bones and quadrate bones flare out sidewards, so that the skull is much wider at its rear lower edges than at the top surface, resulting in a trapezium-shaped profile in posterior view. 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「Brachylophosaurus」の詳細全文を読む スポンサード リンク
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