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''Colymbosaurus'' is a genus of cryptoclidid plesiosaur from the Late Jurassic (Kimmeridgian-Tithonian) of the UK and Svalbard, Norway. There are two currently recognized species, ''C. megadeirus'' and ''C. svalbardensis''. ==Taxonomy== The first remains attributate to ''Colymbosaurus'' were described as a new species of ''Plesiosaurus'', ''P. trochantericus''.〔R. Owen. 1840. Report on British fossil reptiles. Report of the Ninth Meeting of the British Association for the Advancement of Science, Reports on the State of Science 43-126〕 The holotype of the species, NHMUK 31787, a humerus (upper arm bone), comes from the Kimmeridgian Kimmeridge Clay Formation of Shotover, Oxfordshire, England. Richard Owen, however, misidentified the bone as a femur, an identification corrected in an 1871 publication on the geology of Oxfordshire.〔J. Phillips. 1871. Geology of Oxford and the Valley of the Thames. Clarendon Press, Oxford 1-523〕 In the meantime, other plesiosauroid remains were being described from the Kimmeridge Clay by independent workers. The species ''Plesiosaurus megadeirus'' was coined for two partial postcranial specimens in a publication cataloging Mesozoic tetrapod specimens in the collections of the Sedgwick Museum of Earth Sciences at the University of Cambridge.〔H. G. Seeley. 1869. Index to the Fossil Remains of Aves, Ornithosauria, and Reptilia, from the Secondary System of Strata, Arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell, and Co, Cambridge 1-143〕 The name ''Pliosaurus portlandicus'' was coined for a partial hindlimb from Dorset,〔R. Owen. 1869. Monographs on the British Fossil Reptilia from the Kimmeridge Clay III: contains Pliosaurus grandis, Pliosaurus trochanterius, and Pliosaurus portlandicus. Palaeontographical Society Monographs 22(98):1-12〕 while John Whitaker Hulke erected the species ''Plesiosaurus manselii'' for an incomplete postcranial skeleton (NHMUK 40106) from Kimmeridge, Dorset.〔R. Owen. 1869. Monographs on the British Fossil Reptilia from the Kimmeridge Clay III: contains Pliosaurus grandis, Pliosaurus trochanterius, and Pliosaurus portlandicus. Palaeontographical Society Monographs 22(98):1-12〕 Harry Govier Seeley came to recognize ''Plesiosaurus megadeirus'' as generically distinct, and coined the name ''Colymbosaurus'' for the species.〔H. G. Seeley. 1874. Note on some generic modifications of the plesiosaurian pectoral arch. Quarterly Journal of the Geological Society of London 30:436-449〕 He later referred ''Pliosaurus portlandicus'' and ''Plesiosaurus manselii'' to ''Colymbosaurus'' and considered them distinct from ''C. megadeirus'' based on the morphology of the epipodials.〔H. G. Seeley. 1892. The Nature of the Shoulder Girdle and Clavicular Arch in Sauropterygia. Proceedings of the Royal Society of London 51:119-151〕 A review of all nominal species of plesiosauroids from the Late Jurassic of England resulted in the recognition of one species of ''Colymbosaurus'', ''C. trochantericus''. ''P. megadeirus'', ''P. portlandicus'', and ''P. manselii'' were synonymized with ''C. trochantericus''. Because no skull remains were known, ''Colymbosaurus'' was considered possibly a senior synonym of ''Kimmerosaurus'' based on comparisons with referred material of ''Kimmerosaurus''.〔D. S. Brown, A. C. Milner, and M. A. Taylor. 1986. New material of the plesiosaur Kimmerosaurus langhami Brown from the Kimmeridge Clay of Dorset. Bulletin of the British Museum of Natural History 40(5):225-234〕 The distribution of ''Colymbosaurus'' was extended beyond the UK when the Norwegian ''"Tricleidus" svalbardensis'' was recognized as a valid species of ''Colymbosaurus'', ''C. svalbardensis''.〔E. M. Knutsen, P. S. Druckenmiller, and J. Hurum. 2012. Redescription and taxonomic clarification of ‘Tricleidus’ svalbardensis based on new material from the Agardhfjellet Formation (Middle Volgian). Norwegian Journal of Geology 92:175-186〕 This assignment, along with the discovery of new plesiosauroids from Svalbard, prompted a new revision of Kimmeridge Clay cryptoclidids. ''Plesiosaurus trochantericus'' was declared a ''nomen dubium'', being referable to ''Colymbosaurus'' but indeterminate at the species level, while ''Kimmerosaurus'' and ''Plesiosaurus manselii'' were recognized as distinct. Because of this revision, ''megadeirus'' was resurrected as the epithet of the type species of ''Colymbosaurus''.〔Benson RBJ, Bowdler T. 2014. Anatomy of Colymbosaurus (Reptilia, Plesiosauria) from the Kimmeridge Clay Formation of the U.K., and high diversity among Late Jurassic plesiosauroids. Journal of Vertebrate Paleontology 34(5), 1053-1071.〕 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「Colymbosaurus」の詳細全文を読む スポンサード リンク
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