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:''For other meanings see irritation and wikt:irritate.'' ''Irritator'' is a genus of spinosaurid dinosaur that lived in the early Cretaceous Period (Albian stage), around 110 million years ago. Current estimations indicate a length of 8 meters (26 feet).〔Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'' (Winter 2010 Appendix. )〕 In 2010, Gregory S. Paul gave lower estimations of 7.5 metres and one tonne.〔Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 87〕 It was found in Brazil. ''Irritator'' was a theropod with an unusually shaped crest at the rear of its head, and most likely consumed fish. So far the only fossil that has been found was an 80 centimeter long fossil skull in the Romualdo Member, a layer member of the Brazilian Santana formation. This skull strongly resembles the skulls of ''Suchomimus'' and ''Spinosaurus''. The genus is often regarded today as identical (synonymous) with ''Angaturama'', which lived in the same time and the same place as ''Irritator''. ==Discovery== ''Irritator'' was first scientifically described in 1996 by paleontologists Martill, Cruikshank, Frey, Small and Clarke.〔 Its only known fossil, an 80 cm skull discovered in eastern Brazil, was badly obscured by plaster which was added by the commercial fossil-collecting fossil-poachers who illegally sold it (the trade of fossils is prohibited by law in Brazil), in hopes of making the fossil look more complete and valuable. For example, "the posterior portion of the saggital () crest... () fabricated by fossil dealers."〔 The buyers were not aware of the modifications to the illegally collected specimen, and it required them a great deal of work to reconstruct the original features — hence the name. Martill ''et al.'' (1996) wrote that the generic name ''Irritator'' came "from irritation, the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated." The type species is ''I. challengeri'', which honors the character of Professor Challenger in Arthur Conan Doyle's ''The Lost World''.〔〔Isaak, Mark (2008) ("Curiosities of Biological Nomenclature" ). Retrieved 2009-07-26.〕 It is probably synonymous with ''Angaturama limai'', another spinosaurid from the same time and place, whose remains curiously seem to complete ''Irritators skull, meaning that they could belong to the same specimen. The exact discovery site of the ''Irritator'' fossil skull is unknown; the fossil was collected by illegal fossil dealers. The skull and the matrix have been assigned to a rock of the Romualdo Member of the Santana formation due to lithological characteristics; this classification was confirmed by microfossils of the ostracod ''Pattersoncypris''. A questioning of the local fossil dealers resulted in the identification of the discovery site near the village of Buxexé close Santana Do Cariri at the flank of the Chapada do Araripe, at a height of approximately 650 meters. Since rock from the Romualdo Member is indeed exposed there, this discovery site is regarded as very probable for the fossil. The Romualdo Member of the Santana formation is generally assigned to the Albian and thus the last section of the Early Cretaceous. The layers are aged to approximately 110 million years and to have come from a time in which the continents of Africa and South America were still connected with one another in the northern part of Brazil. Material of ''I. challengeri'', not counting that of ''A. limai'', hails from the Romualdo Member of the Santana Formation in Brazil. The holotype is SMNS 58022, from the Stuttgart State Museum of the Natural Sciences, and it consists of an incomplete skull, lacking the anterior (front) portion. The skull was recovered nearly complete and is considered the most complete head find of a Spinosaurid. It is characterized particularly by its unusual length and curved lip region, which is strongly compressed laterally. The overall length of the complete head is estimated at approximately 84 centimeters. It possesses a clear Sagittal crest; such a comb is found also with some other dinosaurs. The teeth exhibit a single embedding of the strongly extended and straight teeth with conical tooth crowns, which indicates a continual tooth change, as new teeth were pushed up between the old ones. The teeth exhibit lengths from 6 to approximately 40 millimeters. In the year 2004 parts of a spinal column were discovered in the Santana Formation.〔Bittencourt, J.DeS., Kellner, A.W.A. 2004. On a Sequence of Sacrocaudal Theropod Dinosaur Vertebrae from the Lower Cretaceous Santana Formation, Northeastern Brazil. Arq. Museu. Naci. Rio De Janeiro. Vol. 62(3):309–320〕 These have been assigned, due to their structure, to the Spinosauridae. With very high probability these fossils belong to ''Irritator'', since this is the so far the only well-known Spinosaurid of the formation.〔 ''Angaturama limai'', from the same time and place as ''Irritator challengeri'', was described by A. Kellner and Diogenes A. Campos in February 1996 on the basis of a fossil from the Santana formation. It was named after Angaturama, a protective spirit in the aboriginal Tupi Indian culture of Brazil, and paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991. Later research uncovered 60% of the complete skeleton, allowing a replica to be made and mounted for exhibit at the Federal University-owned Rio de Janeiro National Museum.〔 ''O Estado de S. Paulo'', May 14, 2009, available at (); ''O Globo'', May 15, 2009, abridgement available at (); university's announcement at ()〕''Angaturama'' was diagnosed by the very strong lateral compression of the snout, and a thin sagittal crest (shape unknown) on top of the premaxillae. Fish may have formed a large part of its diet. However, a pterosaur fossil was found with an ''Angaturama'' tooth embedded in it, pointing to possible predation. Today many sources consider ''Angaturama'' a synonym of ''Irritator''. Some scientists have even speculated that the two partial fossil skulls come from the same individual. Kellner and Campos (2000) as well as Machado and Kellner (2005)〔Machado, E. B., and A. W. A. Kellner. ("Notas Sobre Spinosauridae (Theropoda, Dinosauria)" ), Anuário do Instituto de Geociências - UFRJ, Vol. 28-1, 2005, pp. 158-173.〕 hold however the opinion that the fossils come from two different genera and that ''Angaturama'' had a clearly higher and laterally more flattened head than ''Irritator''. If ''Angaturama'' and ''Irritator'' are actually regarded as a member of the same genus, ''Irritator challengeri'' would be the valid scientific name under the priority rules. The fossil consists only of the front part of the head, which is characterized by the fact that it is very narrow and carries a premaxillary sagittal crest. In the premaxilla a broken-off tooth with partial tooth crown was recovered which corresponds to that of ''Irritator''. Altogether the premaxilla had seven teeth; the third tooth was the largest. The fossil is kept today under the number USP GP/2T-5 in the University of São Paulo. 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「Irritator」の詳細全文を読む スポンサード リンク
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