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Enantiornithes were the most abundant and diverse group of avialans ("birds" in the broad sense) during the Mesozoic Era. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over 50 species of Enantiornithines have been named, but some names represent only single bones, so it is likely that not all are valid. Enantiornithes became extinct at the Cretaceous–Paleogene boundary, along with hesperornithids and all non-avian dinosaurs, and many other groups. Enantiornithes are thought to have left no living descendants. == Discovery and naming == The first Enantiornithes to be discovered were incorrectly referred to modern bird groups (''Gobipteryx minuta''). They were first recognized as a distinct lineage, or "subclass" by Cyril A. Walker, in 1981, based on some partial remains from the late Cretaceous period of what is now Argentina. Since the 1990s, more complete Enantiornithes were discovered and it was demonstrated that a few previously described birds (e.g. ''Iberomesornis'', ''Cathayornis'', ''Sinornis'') had enantiornithe features. "Enantiornithes" means "opposite birds", from Ancient Greek ''enantios'' (''ἐνάντιος'') "opposite" + ''ornithes'' (''όρνιθες'') "birds" . The name was coined by Cyril Alexander Walker in his landmark paper which established the group. In his paper, Walker explained what he meant by "opposite": This refers to an anatomical feature – the articulation of the shoulder bones – which has a concave-convex socket joint that is the reverse of that of modern birds. Specifically, in Enantiornithes, the facet where the ''scapula'' (shoulder blade) meets the ''coracoid'' (the primary bone of the shoulder girdle in vertebrates other than mammals) is a convex knob and the corresponding point on the shoulder blade is concave and dish-shaped. In modern birds, the way the joint articulates is reversed. Walker was not clear on his reasons for giving this name in the etymology section of his paper, and this ambiguity led to some confusion among later researchers. For example, Alan Feduccia stated in 1996: Feduccia's point about the ''tarsometatarsus'' (the combined upper foot and ankle bone) is correct, but Walker did not use this reasoning in his original paper. Walker never described the fusion of the tarsometatarsus as opposite, but rather as "Only partial". Also, it is not certain that Enantiornithes had triosseal canals, since no fossil preserves this feature.〔 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「Enantiornithes」の詳細全文を読む スポンサード リンク
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