Chiappeavis – what is it?

Revised May 11, 2017 with a new look at the ascending process of the prexmaxilla on Chiiappeavis. It’s shorter than I first identified it and I’m happy to correct the error. 

There’s a wonderful new
Early Cretaceous bird out there, Chiappeavis (Figs 1, 2), named for a famous bird paleontologist, Luis Chiappe. The question is, what clade does it belong to?

Figure 1. Chiappeavis nests as an ornithurine bird in the large reptile tree, rather than as an enantiornithine. Click to enlarge. Image from O'Connor et al. 2015. 

Figure 1. Chiappeavis nests as an ornithurine bird in the large reptile tree, rather than as an enantiornithine. Click to enlarge. Image from O’Connor et al. 2015.

From the O’Connor et al. 2016 abstract: The most basal avians Archaeopteryx and Jeholornis have elongate reptilian tails. However, all other birds (Pygostylia) have an abbreviated tail that ends in a fused element called the pygostyle. In extant birds, this is typically associated with a fleshy structure called the rectricial bulb that secures the tail feathers (rectrices). The bulbi rectricium muscle controls the spread of the rectrices during flight. This ability to manipulate tail shape greatly increases flight function. The Jehol avifauna preserves the earliest known pygostylians and a diversity of rectrices. However, no fossil directly elucidates this important skeletal transition. Differences in plumage and pygostyle morphology between clades of Early Cretaceous birds led to the hypothesis that rectricial bulbs co-evolved with the plough-shaped pygostyle of the Ornithuromorpha. A newly discovered pengornithid, Chiappeavis magnapremaxillo gen. et sp. nov., preserves strong evidence that enantiornithines possessed aerodynamic rectricial fans. The consistent co-occurrence of short pygostyle morphology with clear aerodynamic tail fans in the Ornithuromorpha, the Sapeornithiformes, and now the Pengornithidae strongly supports inferences that these features co-evolved with the rectricial bulbs as a “rectricial complex.” Most parsimoniously, rectricial bulbs are plesiomorphic to Pygostylia and were lost in confuciusornithiforms and some enantiornithines, although morphological differences suggest three independent origins.”

Figure 2. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together.

Figure 2. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together. The wing size alone is enough to distinguish this taxon from Pengornis.

Elsewhere on the Internet, at
Theropoddatabase.blogspot.com, M. Mortimer presents arguments that Chiappeavis is just another Pengornis (Figs. 3, 4).

Figure 3. Pengornis reconstructed not from tracing, but from cutting out the bones and putting them back together. Color tracing is used only for the skull elements. This holotype specimen does not have the same morphology or proportions that Chiappeavis has and it nests within the Enantiornithes.

Figure 3. Pengornis reconstructed not from tracing, but from cutting out the bones and putting them back together. Color tracing is used only for the skull elements. This holotype specimen does not have the same morphology or proportions that Chiappeavis has and it nests within the Enantiornithes with Sulcavis.

Indeed
Chaippeavis nests with enantiornithes birds, close to Pengornis.

Figure 4. Pengornis in situ with tracing from O'Connor et al. identifying bones.

Figure 4. Pengornis in situ with tracing from O’Connor et al. identifying bones.

 

 

 

 

References
O’Connor JK, Wang X-L, Zheng X-T, Hu H, Zhang  X-M and  Zhou Z 2016.
An Enantiornithine with a Fan-Shaped Tail, and the Evolution of the Rectricial Complex in Early Birds.Current Biology (advance online publication) DOI: http://dx.doi.org/10.1016/j.cub.2015.11.036

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