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Zhongornis
''Zhongornis'' (meaning "intermediate bird"〔Li, D., Sulliven, C., Zhou, Z. and Zhang, Z. (2010). "Basal birds from China: a brief review." ''Chinese Birds'', 1(2): 83-96 〕) is a genus of primitive birds that lived during the Early Cretaceous. It was found in rocks of the Yixian Formation in Lingyuan City (China), and described by Gao et al. in 2008.〔Gao, Cunling, Chiappe, L.M., Meng, Q., O'connor, J.K., Wang, X., Cheng, X., Liu, J. (2008) "A New Basal Lineage Of Early Cretaceous Birds From China And Its Implications On The Evolution Of The Avian Tail." "Palaeontology" Vol. 51, Part 4, pp. 775-791. 〕
''Zhongornis'' has only one described species, ''Zhongornis haoae''. The only specimen is a fossil slab and counterslab numbered D2455/6. It is in the collection of the Dalian Natural History Museum. It is a fairly complete skeleton about eight centimeters in length. Pores in the bones and unfused sutures in the skeleton indicate that the specimen was a juvenile, but the authors believe that it was developed enough to erect a new taxon on the basis of its unique morphological characters. There are feather impressions preserved on the right hand and also probable tail feathers preserved near the left foot. ''Zhongornis'' had a beaked mouth with no teeth. The tail is proportionately short, has thirteen vertebrae, and no pygostyle. The third finger has only two phalangeal bones, unlike non - avian dinosaurs and ''Confuciusornis'', and more like Enantiornithes and more advanced birds. These features and a cladistic analysis indicate that ''Zhongornis'' is the sister group to all pygostylia, meaning that it is intermediate between long - tailed Avialae like ''Archaeopteryx'' and more advanced taxa like ''Confuciusornis''.
==Evolutionary significance==
''Zhongornis'' provides important anatomical information about the evolutionary transition from primitive basal Avialae like ''Archaeopteryx'', which had a long bony tail and a dinosaur-like third finger, to the more advanced birds like the Enantiornithes, which had reduced third fingers and tails fused into rigid pygostyles. Zhonghornis is the only fossil ever found that seems to be intermediate in these features. It appears to have one less bone in the third finger than ''Archaeopteryx'', and one more than ''Longipteryx'', suggesting that it is an intermediate between the two.〔 ''Zhongornis'' also seems to be intermediate in its tail anatomy. It has only thirteen caudal vertebrae, far less than the 22 in ''Archaeopteryx''. None of the vertebral centra are fused, but the last four do form a continuous lateral flange, implying that this specimen had an incipient pygostyle. Previous to this fossil Sanz et al. (1992) suggested that the evolution of the pygostyle may have proceeded as the numerous vertebrae of the tail became very small and highly ankylosed.〔Sanz, J.L., Bonaparte, J.F. (1992) A New Order of Birds (Class Aves) From the Lower Cretaceous of Spain. Bulletin of the Natural History Museum of Los Angeles, Science Series. 36, 39-49.〕 ''Zhongornis'' suggests that shortening of the tail, and a large reduction in the number of vertebrae, preceded the origin of the pygostyle in the evolution of at least one bird lineage.
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