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Chaoyangia redescribed with new phylogeny of Mesozoic birds

From: Ben Creisler

A new online paper:

Jingmai K. O’Connor & Zhonghe Zhou (2012)
A redescription of Chaoyangia beishanensis (Aves) and a comprehensive
phylogeny of Mesozoic birds.
Journal of Systematic Palaeontology (advance online publication)

We review the enigmatic Chaoyangia beishanensis, one of the earliest
birds described from the Jiufotang Formation, north-eastern China, and
the first to be identified as an ornithurine (Aves: Ornithothoraces)
and thus a member of the clade that includes living birds. A complete
discussion of the validity of this taxon, which once included the
holotype of Songlingornis, is provided, along with a revised
diagnosis. The morphology of Chaoyangia is described, including
extensive comparison with better known, recently discovered
ornithurines as well as several other groups of Mesozoic birds
(Confuciusornithiformes, Sapeornithiformes, Enantiornithes). Although
preserved information is limited, the large number of fused sacral
vertebrae and presence of a distal dorsal process on the ischium are
among the features supporting early hypotheses that the only known
specimen of Chaoyangia represents an ornithurine. Unique among
ornithurines, Chaoyangia possesses two dorsal processes on the
ischium, and thus remains a valid taxon. We include this taxon in a
cladistic analysis to test morphological hypotheses regarding its
systematic position. Although the results of the analysis are highly
resolved and support the referral of Chaoyangia and Zhongjianornis to
Ornithurae, support for the tree overall is very low. Recently
discovered taxa have blurred the once clear morphological gap
separating the two ornithothoracine clades (Ornithurae and
Enantiornithes), and thus the increase in taxonomic diversity has
caused a decrease in the stability of hypothetical relationships.