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.2010 Jan 22;277(1679):219-27.
doi: 10.1098/rspb.2009.0885. Epub 2009 Jul 8.

A new Lower Cretaceous bird from China and tooth reduction in early avian evolution

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A new Lower Cretaceous bird from China and tooth reduction in early avian evolution

Zhonghe Zhou et al. Proc Biol Sci..

Abstract

A new avian genus and species, Zhongjianornis yangi gen. et sp. nov., is reported from the Lower Cretaceous lacustrine deposits of the Jiufotang Formation in Liaoning, northeast China. The new taxon is characterized by possessing the following combination of features: upper and lower jaws toothless, snout pointed, humerus with large and robust deltopectoral crest, second phalanx of the major manual digit longer than the first phalanx, unguals of the alular and major digits of similar length and significantly shorter than the corresponding penultimate phalanges, tibiotarsus slender and more than twice the length of the tarsometatarsus, and metatarsal IV longer than the other metatarsals. Phylogenetic analysis indicates that Zhongjianornis is phylogenetically basal to Confuciusornis and the dominant Mesozoic avian groups, Enantiornithes and Ornithurae, and therefore provides significant new information regarding the diversification of birds in the Early Cretaceous. It also represents the most basal bird that completely lacks teeth, suggesting that tooth loss was more common than expected in early avian evolution and that the avian beak appeared independently in several avian lineages, most probably as a response to selective pressure for weight reduction. Finally, the presence of a significantly enlarged humeral deltopectoral crest suggests that Zhongjianornis shares with other basal birds such as Jeholornis, Sapeornis and Confuciusornis a distinctive mode of adaptation for flight contrasting with that seen in more advanced birds, which instead possess an elongated sternum and a prominent keel.

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Figures

Figure 1.
Figure 1.
Holotype ofZhongjianornis yangi gen. et sp. nov. (IVPP V15900). Scale bar, 5 cm.
Figure 2.
Figure 2.
Line drawing of the holotype ofZhongjianornis yangi gen. et sp. nov. (IVPP V15900). Abbreviations: ca, caudal vertebra; ce, cervical vertebra; co, coracoid; dI-1, first phalanx of alular digit; dII-1, first phalanx of major digit; dII-2, second phalanx of major digit; fe, femur; fi, fibula; fu, furcula; hu, humerus; il, ilium; is, ischium; mcI, alular metacarpal, mcII, major metacarpal; mcIII, minor metacarpal; mtI, metatarsal I; pd, pedal digits; pu, pubis; r, radius; sc, scapula; st, sternum; sy, synsacrum; ti, tibia; tmt, tarsometatarsus; tv, thoracic vertebra; u, ulna; up, uncinate process of rib. Scale bar, 5 cm.
Figure 3.
Figure 3.
(a) Skull of the holotype ofZhongjianornis yangi gen. et sp. nov. (IVPP V15900). (b) Line drawing of the holotype skull ofZhongjianornis yangi gen. et sp. nov. (IVPP V15900). Abbreviations: an, angular; ar, articular; bs, basisphenoid; de, dentary; fr, frontal; ju, jugal; ma, maxilla; na, nasal; pa, parietal; ?pal, ?palatine; pm, premaxila; ?pt, ?pterygoid; sa, surangular; sp, splenial bone. Scale bar, 1 cm.
Figure 4.
Figure 4.
Close-up photos ofZhongjianornis yangi gen. et sp. nov. (IVPP V15900), showing (a) the thoracic ribs and uncinate processes, (b) the pectoral girdle, and (c) the hand. Abbreviations: dI-2, second phalanx of the alular digit; dII-3, third phalanx of the major digit; dIII-1, first phalanx of the minor digit; ul, ulnare; see figure 2 for other abbreviations. Scale bar, 1 cm.
Figure 5.
Figure 5.
Close-up photos ofZhongjianornis yangi gen. et sp. nov. (IVPP V15900), showing (a) the pelvis and (b) the right foot. Abbreviations: mtII, metatarsal II; mtIII, metatarsal III; mtIV, metatarsal IV; pdI, pedal I; pdII, pedal II; pdIV, pedal IV; see figure 2 for other abbreviations. Scale bar, 1 cm.
Figure 6.
Figure 6.
Phylogeny ofZhongjianornis yangi gen. et sp. nov. Phylogenetic analysis was conducted using NONA 2.0 and WinClada. All characters were unordered. A total of 205 morphological characters were used, following Zhouet al. (2008). The data matrix from Zhouet al. (2008) was used in a revised form. Tree length = 487; CI = 0.55; RI = 0.77. The cladogram is based on the strict consensus of four most parsimonious trees.
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