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Yanornis
''Yanornis'' (Chinese: 燕鸟) is an extinct genus of fish-eating Early Cretaceous birds. Two species have been described, both from Liaoning province, China: ''Yanornis martini'', based on several fossils found in the 120-million-year-old Jiufotang Formation at Chaoyang,〔Zhou Z., Clarke, J.A. and Zhang F. (2002): ''Archaeoraptor'' 's better half. ''Nature'', 420: 285. (HTML abstract) (Supplementary information )〕 and ''Yanornis guozhangi'', from the 124-million-year-old Yixian Formation.〔Wang, Ji, Teng and Jin (2013). "A new species of ''Yanornis'' (Aves: Ornithurae) from the Lower Cretaceous strata of Yixian, Liaoning Province." ''Geological Bulletin of China'', 32(4), 601-606.〕
==Description==
''Y. martini'' was the size of a chicken,〔Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'' (Winter 2010 Appendix. )〕 had a long skull with about 10 teeth in the upper jaw and 20 teeth in the lower jaw, and was both able to fly and walk well, having a well-developed U-shaped furcula (wishbone).
The absence of the prefrontal bone and the non-diapsid skull allows ''Yanornis'' to be classified as an ornithuromorph, a member of a group of stem-birds which also includes the common ancestor of living birds. Similarly, its scapula and coracoid had evolved the basic shape and layout as in modern birds, enabling ''Yanornis'' to lift its wings far above its back for an efficient upstroke. It was probably a more efficient flyer compared to enantiornithines (which have the modern condition in a less well-developed form), and especially compared to ''Confuciusornis'' and ''Archaeopteryx'', which were only marginally able to perform upstrokes.〔 (2006): Scapular orientation in theropods and basal birds, and the origin of flapping flight. ''Acta Palaeontologica Polonica'' 51(2): 305–313. (PDF fulltext )〕 To allow for the necessarily large flight muscles, the sternum of ''Yanornis'' was longer than it was wide, again representing an essentially modern condition.〔 (2004) Enantiornithine Bird with Diapsidian Skull and Its Dental Development in the Early Cretaceous in Liaoning, China. ''Acta Geologica Sinica'' 78(1): 1-7. (PDF fulltext )〕
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