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''Siamotyrannus'' (meaning "Siamese Tyrant") is a genus of carnivorous theropod dinosaur from the early Cretaceous of Thailand. In 1993, Somchai Traimwichanon found a partial skeleton of a large theropod at the Phu Wiang 9 site in Khon Kaen. In 1996, Eric Buffetaut, Varavudh Suteethorn and Haiyan Tong named and described the type species ''Siamotyrannus isanensis''. The generic name is derived from the old Thai kingdom of Siam, and a Latinised Greek ''tyrannus'', meaning "tyrant", in reference to a presumed membership of the Tyrannosauridae. The specific name is derived from Thai ''isan'', "northeastern part", referring to the provenance from northeast Thailand.〔 The holotype, PW9-1, was found in the Sao Khua Formation, dating from the Berriasian-Barremian. It includes the left half of the pelvis, five rear dorsal vertebrae, the sacrum with five sacrals, and thirteen front tail vertebrae.〔Buffetaut, E., Suteethorn, V. and Tong, H. 1996. "The earliest known tyrannosaur from the Lower Cretaceous of Thailand". ''Nature'' 381: 689-691〕 In 1998, a tibia and some individual teeth were referred to the species.〔Buffetaut, E. and Suteethorn, V., 1998, "Early Cretaceous dinosaurs from Thailand and their bearing on the early evolution and biogeographical history of some groups of Cretaceous dinosaurs", In: Lucas, Kirkland and Estep, (eds.). ''Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History Bulletin 14''. p. 205-210〕 ''Siamotyrannus'' is a large theropod. Buffetaut estimated its length at seven meters. In 2010, Gregory S. Paul estimated the length at six metres, the weight at half a ton.〔Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 91〕 A possible autapomorphy, unique derived trait, is the possession of two vertical ridges on the ilium. The second and third sacrals are strongly transversely flattened. As evidenced by its name, it was originally thought to be a tyrannosauroid and even a tyrannosaurid,〔 though due to lacking some of the primary tyrannosauroid synapomorphies that define the clade, its position here is not certain.〔Rauhut, Oliver W. M. Special Papers in Palaeontology: ''The Interrelationships and Evolution of Basal Theropod Dinosaurs'' (No. 69). The Palaeontological Association: 2003〕 Some analyses have categorized ''Siamotyrannus'' as a primitive carnosaur rather than a basal tyrannosauroid, and it has several features that may determine it to be an allosaurid or a sinraptorid.〔Holtz, Thomas R. et al. (2004). "Basal Tetanurae." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): ''The Dinosauria'', 2nd, Berkeley: University of California Press. p. 101 ISBN 0-520-24209-2〕 In 2012 Matthew Carrano e.a. found a position in the Metriacanthosaurinae.〔Carrano, M. T.; Benson, R.B.J.; Sampson, S.D., 2012, "The phylogeny of Tetanurae (Dinosauria: Theropoda)". ''Journal of Systematic Palaeontology'' 10(2): 211–300〕 ==References== 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「Siamotyrannus」の詳細全文を読む スポンサード リンク
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