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Nemegtosauridae is a family of probably titanosaurian sauropod dinosaurs based originally on two late Cretaceous Mongolian species known only from their diplodocid-like skulls: ''Nemegtosaurus'' and ''Quaesitosaurus''. Authorities disagree as to the relationship of these two genera with other sauropods, and indeed whether they even constitute a valid family. More recently, additional sauropods have been added to this group, and cladistic methodology has been used to shed further light on the evolutionary relationships of these animals. It is named after the Nemegt Basin in Mongolia, where some of its fossils were found. ==History of classification== McIntosh 1990 included both these animals in the family Diplodocidae, subfamily Dicraeosaurinae, as they resemble the skull of ''Dicraeosaurus'', although differing in certain details. Although the skull of ''Nemegtosaurus'' was found in the same formation as the headless skeleton of ''Opisthocoelicaudia'', McIntosh rejects the possibility that they belong to the same animal, as ''Nemegtosaurus'' is diplodocid-like, but ''Opisthocoelicaudia'' camarasaur-like. Upchurch 1995 placed the two genera in their own family, without giving a cladistic definition. However, the name first appeared in print a few weeks earlier in a paper by Barrett and Upchurch. Wilson in 2002 referred the two genera to the family Nemegtosauridae, and on the basis of cladistic analysis, transferred them from the Diplodocoidea to the Titanosauria Apesteguia (2004), in a paper describing a new Patagonian sauropod, ''Bonitasaura salgadoi'', may have been the first to properly define the taxon, although without the use of cladistic analysis: the stemclade consisting of all titanosaurs more closely related to ''Nemegtosaurus'' than to ''Saltasaurus''. He argued for a close relationship between ''Nemegtosaurus'', ''Quaesitosaurus'', ''Rapetosaurus'', and ''Bonitasaura'' and referred to the previous phylogenetic analysis and use of Nemegtosauridae by Wilson (2002). Upchurch et al. 2004 returned the Nemegtosauridae to the Diplodocoidea, and defined the former as the stem clade consisting of all Diplodocoidea closer to ''Nemegtosaurus'' than to ''Diplodocus''. The only known species were ''Nemegtosaurus'' itself and ''Queasitosaurus''. Curry Rogers 2005, in one of the most complete cladistic analysis of the Titanosauria to date, returns both ''Nemegtosaurus'' and ''Quaesitosaurus'' to the titanosaurs, but rejects the validity of both the family Nemegtosauridae and the clade concepts given under that name. ''Quaesitosaurus'' is placed in the Saltasaurinae and ''Nemegtosaurus'' in a new, unnamed "''Rapetosaurus'' clade" (which, under ICZN rules, would, if named, be termed subfamily Nemegtosaurinae or tribe Nemegtosaurini, depending on its position). She places ''Opisthocoelicaudia'' in a separate clade, the Opisthocoelicaudiinae. All three clades are included in the Saltasauridae (= Titanosauridae). Unaware of Apesteguia's work, Wilson (2005) proposed a definition identical to his and further clarified the anatomy and relationships of the central genus ''Nemegtosaurus''. He thus also defines the Nemegtosauridae as a stem-based clade that includes all titanosaurs more closely related to ''Nemegtosaurus'' than to ''Saltasaurus''. He also suggests that ''Opisthocoelicaudia'' may eventually be shown to be a junior synonym of ''Nemegtosaurus''. ImageSize = width:1500px height:auto barincrement:15px PlotArea = left:10px bottom:50px top:10px right:10px Period = from:1824 till:2100 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:50 start:1824 ScaleMinor = unit:year increment:10 start:1824 TimeAxis = orientation:hor AlignBars = justify Colors = #legends id:CAR 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「Nemegtosauridae」の詳細全文を読む スポンサード リンク
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