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evolution of dinosaurs
: ''This article gives an outline and examples of dinosaur evolution. For a detailed list of interrelationships see Dinosaur classification.''
Dinosaurs evolved within a single lineage of archosaurs 232-234 Ma (million years ago) in the Ladinian age, the latter part of the middle Triassic. Dinosauria is a well-supported clade, present in 98% of bootstraps. It is diagnosed by many features including loss of the postfrontal on the skull and an elongate deltopectoral crest on the humerus.〔Weishampel, Dodson & Osmolska, 2004, The Dinosauria〕
==Origins amongst archosaurs==
The process leading up to the Dinosauromorpha and the first true dinosaurs can be followed through fossils of the early Archosaurs such as the Proterosuchidae, ''Erythrosuchidae'' and ''Euparkeria'' which have fossils dating back to 250 Ma, through mid-Triassic archosaurs such as ''Ticinosuchus'' 232-236 Ma. Crocodiles are also descendants of mid-Triassic archosaurs.〔
Dinosaurs can be defined as the last common ancestor of birds (Saurischia) and ''Triceratops'' (Ornithischia) and all the descendants of that ancestor. With that definition, the pterosaurs and several species of archosaurs narrowly miss out on being classified as dinosaurs. The pterosaurs are famous for flying through the Mesozoic skies on leathery wings and reaching the largest sizes of any flying animal that ever existed. Archosaur genera that also narrowly miss out on being classified as dinosaurs include ''Schleromochlus'' 220-225 Ma, ''Lagerpeton'' 230-232 Ma and ''Marasuchus'' 230-232 Ma.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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