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Hypacrosaurus
''Hypacrosaurus'' (meaning "near the highest lizard" (υπο-, ''hypo-'' = less + ακρος, ''akros'', high ), because it was almost but not quite as large as ''Tyrannosaurus'') was a genus of duckbill dinosaur similar in appearance to ''Corythosaurus''. Like ''Corythosaurus'', it had a tall, hollow rounded crest, although not as large and straight. It is known from the remains of two species that spanned 75 to 67 million years ago, in the Late Cretaceous of Alberta, Canada, and Montana, USA, and is the latest hollow-crested duckbill known from good remains in North America. It was an obscure genus until the discovery in the 1990s of nests, eggs, and hatchlings belonging to ''H. stebingeri'' .
==Description==
''Hypacrosaurus'' is most easily distinguished from other hollow-crested duckbills (lambeosaurines) by its tall neural spines and the form of its crest. The neural spines, which project from the top of the vertebrae, are 5 to 7 times the height of the body of their respective vertebrae in the back, which would have given it a tall back in profile. The skull's hollow crest is like that of ''Corythosaurus'', but is more pointed along its top, not as tall, wider side to side, and has a small bony point at the rear.〔 Unlike other lambeosaurines, the passages for the airways do not form an S-curve in the crest (at least not in ''H. altispinus''). The animal is estimated to have been around 9.1 meters long (30 feet),〔 and to have weighed up to 4.0 tonnes (4.4 tons).〔 As with most duckbills, its skeleton is otherwise not particularly remarkable, although some pelvic details are distinctive. Like other duckbills, it was a bipedal/quadrupedal herbivore. The two known species, ''H. altispinus'' and ''H. stebingeri'', are not differentiated in the typical method, of unique characteristics, as ''H. stebingeri'' was described as transitional between the earlier ''Lambeosaurus'' and later ''Hypacrosaurus''. Photographs of an adult ''H. stebingeri'' skull show an animal that looks very similar to ''H. altispinus''.
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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