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''Chasmosaurus'' ( ) is a genus of ceratopsid dinosaur from the Upper Cretaceous Period of North America. Its name means 'opening lizard', referring to the large openings (fenestrae) in its frill (Greek ''chasma'' meaning 'opening' or 'hollow' or 'gulf' and ''sauros'' meaning 'lizard'). With a length of and a weight of , ''Chasmosaurus'' was a ceratopsian of average size. Like all ceratopsians, it was purely herbivorous. It was initially to be called ''Protorosaurus'', but this name had been previously published for another animal. All specimens of ''Chasmosaurus'' were collected from the Dinosaur Park Formation of the Dinosaur Provincial Park of Alberta, Canada. ''C. russelli'' comes from the lower beds of the formation while ''C. belli'' comes from middle and upper beds. ==Discoveries and species== In 1898, Lawrence Morris Lambe of the Geological Survey of Canada made at the Berry Creek the first discovery of ''Chasmosaurus'' remains, holotype NMC 491, a parietal bone that was part of a neck frill.〔 Although recognizing that his find represented a new species, Lambe thought this could be placed in a previously-known short-frilled ceratopsian genus: ''Monoclonius''.〔 He erected the new species ''Monoclonius belli'' to describe his finding.〔 The specific name honoured collector Walter Bell.〔Lambe, L.M., 1902, "New genera and species from the Belly River Series (mid-Cretaceous)", ''Geological Survey of Canada Contributions to Canadian Palaeontology'' 3(2): 25-81〕 However, in 1913, Charles Hazelius Sternberg and his sons found several complete "M. belli" skulls in the middle Dinosaur Park Formation of Alberta, Canada.〔 In January 1914, Lambe named all these finds as a separate genus: ''Protorosaurus'', the name indicating an ancestry to ''Torosaurus''.〔Lambe, L.M., 1914, "On the forelimb of a carnivorous dinosaur from the Belly River Formation of Alberta, and a new genus of Ceratopsia from the same horizon, with remarks on the integument of some Cretaceous herbivorous dinosaurs", ''The Ottawa Naturalist'' 27(10): 129-135〕 However, this name quickly was shown to be preoccupied by a Permian reptile, ''Protorosaurus'', described by Meyer in 1836. Therefore Lambe created the replacement name ''Chasmosaurus'' in February 1914.〔 It is derived from Greek χάσμα, ''khasma'', "opening" or "divide" and refers to the very large parietal fenestrae in the skull frill. Lambe now also assigned a paratype, specimen NMC 2245 found by the Sternbergs in 1913 and consisting of a largely complete skeleton, including skin impressions.〔Lambe, L.M., 1914, "On ''Gryposaurus notabilis'', a new genus and species of trachodont dinosaur from the Belly River Formation of Alberta, with a description of the skull of ''Chasmosaurus belli''", ''The Ottawa Naturalist'' 27: 145-155〕 Since that date, more remains, including skulls, have been found that have been referred to ''Chasmosaurus'', and several additional species have been named within the genus.〔 Today some of these are considered to only reflect a morphological variation among the known sample of ''Chasmosaurus belli'' skulls;〔 others are seen as valid species of ''Chasmosaurus'' or as separate genera. In 1933 Barnum Brown named ''Chasmosaurus kaiseni'', honouring Peter Kaisen and based on skull AMNH 5401, differing from ''C. belli'' in having very long brow horns.〔Brown, B., 1933, "A new longhorned Belly River ceratopsian", ''American Museum Novitates'' 669: 1-3〕 This form is perhaps related to ''Chasmosaurus canadensis'' ('from Canada') named by Thomas M. Lehman in 1990.〔T.M. Lehman, 1990, "The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics", In: K. Carpenter and P. J. Currie (eds.), ''Dinosaur Systematics: Perspectives and Approaches'', Cambridge University Press, Cambridge, pp. 211-229〕 The latter species, originally'' Monoclonius canadensis'' Lambe 1902, had been described as ''Eoceratops canadensis'' by Lambe in 1915. ''Eoceratops'' and the long-horned ''Chasmosaurus kaiseni'' are now provisionally thought to be exemplars of ''Mojoceratops''. Richard Swann Lull in 1933 named an unusual, short-muzzled skull, specimen ROM 839 (earlier ROM 5436) collected in 1926, as ''Chasmosaurus brevirostris'', "with a short snout".〔Lull, R.S., 1933, ''A revision of the Ceratopsia or horned dinosaurs''. Memoirs of the Peabody Museum of Natural History 3(3): 1-175〕 This has been seen as a junior synonym of ''C. belli''.〔 Charles Mortram Sternberg added ''Chasmosaurus russelli'' in 1940, based on specimen NMC 8800 from southwestern Alberta (lower Dinosaur Park Formation). The specific name honours Loris Shano Russell.〔〔Sternberg, C.M., 1940, "Ceratopsidae from Alberta", ''Journal of Paleontology'' 14(5): 468-480〕 Thomas Lehman described ''Chasmosaurus mariscalensis'' in 1989 from Texas,〔Lehman, T.M., 1989, "''Chasmosaurus mariscalensis'', sp. nov., a new ceratopsian dinosaur from Texas", ''Journal of Vertebrate Paleontology'', 9(2): 137-162〕 which has now been renamed ''Agujaceratops''. The most recently described species is ''Chasmosaurus irvinensis'' named in 2001,〔R.B. Holmes, C.A. Forster, M.J. Ryan and K.M. Shepherd, 2001, "A new species of ''Chasmosaurus'' (Dinosauria: Ceratopsia) from the Dinosaur Park Formation of southern Alberta", ''Canadian Journal of Earth Sciences'' 38: 1423–1438〕 which stems from the uppermost beds of the Dinosaur Park Formation. This species was given its own genus, ''Vagaceratops'', in 2010. In 1987, Gregory S. Paul renamed ''Pentaceratops sternbergii'' into ''Chasmosaurus sternbergi'',〔Paul, G.S., 1987, "The science and art of reconstructing the life appearance of dinosaurs and their relatives: a rigorous how-to guide", pp 4-49 in: ''Dinosaurs Past and Present Volume II'', Natural History Museum of Los Angeles County〕 but this has found no acceptance. In 2000, George Olshevsky renamed ''Monoclonius recurvicornis'' Cope 1889 into ''Chasmosaurus recurvicornis'' as its fossil material is likely chasmosaurine;〔Olshevsky, G. 2000. ''An Annotated Checklist of Dinosaur Species by Continent''. George Olshevsky, Publications Requiring Research, San Diego, 157 pp〕 this is a ''nomen dubium''. Today, only two species are seen as valid: ''C. belli'' and ''C. russelli''. They show small differences in morphology and a difference in stratigraphy, as ''C. russelli'' is found in the older lower Dinosaur Park Formation and ''C. belli'' in the middle Dinosaur Park Formation of the Campanian,〔Maidment, S.C.R., and Barrett, P.M., 2011, "A new specimen of ''Chasmosaurus belli'' (Ornithischia: Ceratopsidae), a revision of the genus, and the utility of postcrania in the taxonomy and systematics of ceratopsid dinosaur", ''Zootaxa'', 2963: 1-47〕 together spanning a time period of 76.5 to 75.5 million years ago. Apart from the holotype and paratype several additional specimens of ''C. belli'' are known. These include AMNH 5422, AMNH 5402, ROM 843 (earlier ROM 5499) and NHMUK R4948, all (partial) skeletons with skull; and YPM 2016, a skull. Apart from its holotype ''C. russelli'' is known from its paratype CMN 8803, a skull frill; CMN 41933, a rear skull frill; RTMP 81.19.175, the right side of a skull and CMN 2280, a partial skeleton with skull found by the Sternbergs in 1914. 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「Chasmosaurus」の詳細全文を読む スポンサード リンク
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