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Stygimoloch
''Stygimoloch'' (meaning "demon from the Styx") is a genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 66 million years ago. It is currently known from the Hell Creek Formation, Ferris Formation, and Lance Formation of the Western Interior (United States), where it lived alongside ''Tyrannosaurus'' and ''Triceratops''. The type species, ''S. spinifer'' (meaning "thorny devil from the Styx (river of death)"), was described by British vertebrate paleontologist Peter Galton and German paleontologist Hans-Dieter Sues of the National Museum of Natural History in 1983.〔Galton, P. M. and H. D. Sues (1983). "New data on pachycephalosaurid dinosaurs (Reptilia: Ornithischia) from North America." Canadian Journal of Earth Sciences 20: 462-472.〕 ''Stygimoloch'' is characterized by clusters of spikes on the back of the skull, in which a long central horn is surrounded by 2-3 smaller hornlets, and a tall, narrow dome.〔Goodwin, M. B., E. A. Buchholtz, et al. (1998). "Cranial anatomy and diagnosis of Stygimoloch spinifer." Journal of Vertebrate Paleontology 18(2): 363-375.〕 ''Dracorex'' has similar but shorter hornlets and lacks a dome, and has been interpreted as either a distinct species, or a juvenile or female of ''Pachycephalosaurus'' or ''Stygimoloch''. It has also been proposed that ''Stygimoloch'' represents partially grown individuals of ''Pachycephalosaurus''.
==Description==
It is a relatively large pachycephalosaur, with the skull being about 46 centimeters long (18 in).〔(【引用サイトリンク】title=Quién es el Stygimoloch? )〕 Among North American pachycephalosaurs, only ''Pachycephalosaurus'' is larger. Unlike other pachycephalosaurs, the domed skull is relatively small, slightly flattened from side to side, and pear-shaped; even when isolated this unusual dome can easily be distinguished from the broader, larger domes of ''Pachycephalosaurus''.
While the dome is reduced in size, the ornamentation over the skull is more elaborate than in any other pachycephalosaur. Short, conical hornlets covered the nose, and the back corners of the skull bore an enormous pair of massive, backward-pointing spikes, up to 5 centimeters in diameter (2 in) and 15 centimeters long (6 in); these are surrounded by two or three smaller spikes. The function of this unusual ornamentation is unknown. Even if other pachycephalosaurs did butt heads (which is a subject of continuing debate), the small dome of ''Stygimoloch'' suggests that this behavior was not as important. Instead, the skull ornament might have functioned for display, may have been used for self-defense, or perhaps were locked together and used in shoving matches, like the horns of deer. Another possibility is that the squamosal horns were used to inflict pain during flank-butting.
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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