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''Dracorex'' is a dinosaur genus of the family Pachycephalosauridae, from the Late Cretaceous of North America. The type (and only known) species is ''Dracorex hogwartsia'', meaning "dragon king of Hogwarts". It is known from one nearly complete skull (the holotype TCMI 2004.17.1), as well as four cervical vertebrae: the atlas, third, eighth and ninth. These were discovered in the Hell Creek Formation in South Dakota by three amateur paleontologists from Sioux City, Iowa. The skull was subsequently donated to the Children's Museum of Indianapolis for study in 2004, and was formally described by Bob Bakker and Robert Sullivan in 2006.〔Bakker, R. T., Sullivan, R. M., Porter, V., Larson, P. and Saulsbury, S.J. (2006). "''Dracorex hogwartsia'', n. gen., n. sp., a spiked, flat-headed pachycephalosaurid dinosaur from the Upper Cretaceous Hell Creek Formation of South Dakota." in Lucas, S. G. and Sullivan, R. M., eds., Late Cretaceous vertebrates from the Western Interior. ''New Mexico Museum of Natural History and Science Bulletin'' 35, pp. 331–345. ()〕 However, Jack Horner ''et al.'' suspect that it is a juvenile ''Pachycephalosaurus'' and an analysis of pachycephalosaur fossils by a joint team from the University of California, Berkeley and the Museum of the Rockies has questioned the validity of two named genera of pachycephalosaur, ''Dracorex'' and ''Stygimoloch''. According to the team, specimens of ''Dracorex'' and ''Stygimoloch'' might actually represent earlier growth stages of ''Pachycephalosaurus''. As this article on the UC Berkeley website says, "The confusion is traced to their bizarre head ornaments, ranging from shields and domes to horns and spikes, which changed dramatically with age and sexual maturity, making the heads of youngsters look very different from those of adults." ==Description== ''Dracorex'', an herbivore, had a skull with spiky horns, bumps, and a long muzzle. The species also sports well-developed supratemporal fenestrae and a heavily armored flat skull—lacking the characteristic pachycephalosaurid dome. Coupled with these two features is the excessive number of osteoderms in the form of irregular osteodermal crust: a number of nodes, larger hornlets, and spikes. Disregarding this, ''Dracorex'' is physically comparable to ''Stygimoloch''. In the Pachycephalosauridae, the Asian taxa include a number of (somewhat) flat-headed pachycephalosaurs (''Homalocephale calathocercos'', ''Goyocephale lattimorei'', and ''Wannanosaurus yansiensis''). However, prior to the discovery of ''Dracorex'', the only semi-flat-headed pachycephalosaur from North America was ''Stegoceras validum'' (inclusive of ''Ornatotholus browni''). Even then, the semi-flat-headed trait was only present in juveniles of the species. Aside from having a flat, nodal skull, the most prominent feature of ''Dracorex'' is the pair of huge and unrestricted superior temporal openings. The supratemporal fenestrae are much larger front-to-back and side-to-side than in ''Homalocephale'', and larger than in ''Goyocephale''. Only a fragmentary ''Wannanosaurus'' skull shows fenestrae as large as those of ''Dracorex''. This fenestral architecture has been seen in ancient archosaurs, but not in other pachycephalosaurs. Consequently, if unreduced superior fenestrae are morphologically primitive, then ''Dracorex'' is more primitive in the temporal region than any other known pachycephalosaur. However, Sullivan (2003, 2006) demonstrated that the oldest known pachycephalosaurs were, in fact, fully domed, and that the flat-headed morphology appeared later in the fossil record. This suggests that doming may be primitive for pachycephalosaurs and that a reversion to the non-domed, flat-headed state is a secondary (derived) character reversion, coupled with the re-opening of the supratemporal fenestrae. Indeed, while ''Stegoceras'' has been considered to be transitional between domed and flat-headed taxa, it may indicate the beginning of a character reversion to suppression of doming and opening of the supratemporal fenestrae in some taxa. The excavated specimen was most likely a young adult. However, based on the beginning of ossification of the mid-cervical arch with the centrum, it was near maturity.〔 The animal was approximately 3 m (10 feet) long. 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「Dracorex」の詳細全文を読む スポンサード リンク
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