New Sapeornis

["Brad McFeeters" <archosauromorph2@hotmail.com>]

Zhou Zhonghe and Fucheng Zhang, 2003.  Anatomy of the primitive bird 
Sapeornis chaoyangensis from the Early Cretaceous of Liaoning, China. Can. 
J. Earth Sci. 40(5): 731-747

Abstract: Two new, nearly completely articulated skeletons of Sapeornis 
chaoyangensis provide much new information about the anatomy of this basal 
avian, particularly in the skull, pectoral girdle, forelimb, and hind limb. 
This new material shows that the hand of Sapeornis, with a phalangeal 
formula of "2?3?2," was more derived than previously reconstructed. The 
skeleton of Sapeornis has several unique features, such as a distinctively 
elongated fenestra on the proximal end of the humerus, a robust furcula with 
a distinctive hypocleidum, and an elongated forelimb. Sapeornis exhibits a 
combination of derived and primitive features, including a short, robust 
non-strut-like coracoid and a fibula reaching the distal end of the tarsal 
joint (as in Archaeopteryx), a pygostyle, reduced manual digits, and a 
well-fused carpometacarpus (as in more advanced birds). These features 
further indicate the mosaic pattern in the early evolution of birds and 
confirm the basal position of Sapeornis near Archaeopteryx and Jeholornic in 
the phylogeny of early birds. The preservation of gastroliths in one of the 
new specimens also represents the first Chinese Mesozoic bird with such 
evidence, indicating a herbivorous feeding habit and providing further 
evidence for our understanding of the diet diversification in early avian 
evolution.

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