Updated October 23, 2015 with new skull data.
Yesterday we looked at Eosinopteryx (Godefroit et al. 2013, Middle-Late Jurassic, Tiaojishan Formation) and discussed a possible new nesting site (Fig. 1) based on a lack of included short-coracoid taxa preceding Archaeopteryx to compare it with. By comparison, Cosesaurus has a “flapping”-type coracoid and it has much less wing tissue trailing its front limbs. So the long, locked-down coracoid in bird predecessors was among the last traits to evolve, post-dating the appearance of elongated forelimb feathers.
Addendum: The analysis of Godefroit et al. (2013) was based on and provided only a segment of an earlier analysis that DID include these more primitive taxa. Thus my doubt is reduced considerably as all pertinent taxa were included. The skull on DGS
Not sure if a skull reconstruction was provided by Godefroit et al. (2013) or not. (not) I’d still like to see the paper. (I have the paper now. ) Even so, in order to create yesterday’s reconstruction I applied DGS (digital graphic segregation) to the skull (Fig. 2). I don’t know birds as well as dinosaurs and did not attempt a palate reconstruction. If I made any mistakes, please send me an email. (Figure 2 is an update based on higher resolution images of an earlier posted figure.)
The skull of Eosinopteryx traced using Photoshop, a process known as DGS or Digital Graphic Segregation. For followers of this blog, these updated images reflect the importance of high resolution data in using DGS. Much like the Hale telescope, greater resolution enables the identification of finer lines and bones. This demonstrates that its not the mechanics of the technique so much, as the intimate knowledge long months of study provides when employed, and higher resolution really helps. (Higher resolution image did provide improved data.)
The premaxilla includes at least three elongated teeth (here seen from the inside). The saddle-shaped nasal was broken into at least four pieces during crushing. The maxilla is decayed beyond the normal fenestration. Here (Fig. 3) I reconstruct it conventionally. There is no elongated posterior lacrimal process and vestigial anterior process as Godefroit et al. (2013) reported. Rather the lacrimal is similar to that of other theropods. They did not provide a reconstruction. An earlier reconstruction of mine misplaced the quadrate articulation, which is repaired here. It also did not recognize the posterior mandible, which in situ is separated from the articular area. But here (Fig. 3) this has been repaired, thanks to theropod expert, M. Mortimer, for pointing this out. It was also overlooked by Godefroit et al. (2013, Fig. 2).
Godefroit P, Demuynck H, Dyke G, Hu D, Escuillié FO and Claeys P. 2013. Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature Communications 4: 1394. doi:10.1038/ncomms2389
Paul GS 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press 320 pp.