Re: Chaoyangia redescribed with new phylogeny of Mesozoic birds

[Tim Williams <tijawi@gmail.com>]

This new phylogeny recovers a clade comprising _Limenavis_ and
hesperornithiforms.  I find this quite curious, because _Limenavis_ is
known only from the wing skeleton of a volant bird, and the wings of
hesperornithiforms were vestigial.  What characters could possibly
unite a _Limenavis_ + Hesperornithiformes clade?




On Thu, Jun 21, 2012 at 1:38 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> From: Ben Creisler
> bcreisler@gmail.com
>
> 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)
> DOI:10.1080/14772019.2012.690455
> http://www.tandfonline.com/doi/abs/10.1080/14772019.2012.690455
>
>
>
> 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.