Updated October 23, 2015 with a new skull.
Eosinopteryx brevipenna (Godefroit et al. 2013, Middle-Late Jurassic, Tiaojishan Formation) is represented by a new complete skeleton. It was a feathered theropod dinosaur about 30 cm long. The forelimb feathers were quite long (Fig. 1), but the tail feathers were not.
Paravian? or Preavian?
We’ve been looking for a feathered theropod without elongated coracoids to precede Archaeopteryx. We also need this taxon to be not pre-oviraptorid or pre-alvarezsaurid. The authors argue, with a very extensive phylogenetic analysis, that this is a troodontid resembling Anchiornis, with less extensive feathers on the hind limbs and tail. Anchiornis greatly resembled Archaeopteryx and is, therefore, closely related. Of that, there is no doubt.
Why There is Doubt
I have not created a competing analysis. Checking out Greg Paul’s figure of Anchiornis (Paul 2010), I note his Anchiornis has the short torso and elongated coracoid also seen in Archaeopteryx, troodontids and deinonychosaurs. On October 23, 2015 I added Eosinopteryx to the large reptile tree where it nests between Aurornis and Archaeopteryx as the last theropod that was not a bird.
What sets Eosinopteryx apart from these?
A short coracoid with a broad curved ventral rim – Therefore Eosinopteryx did not flap and was not descended from flappers. We haven’t seen a terrestrial descendant of Archaeopteryx yet without elongated coracoids. For more on this, compare Huaxiagnathus (with its short coracoid) to Velociraptor, (with its long, tall coracoid). Otherwise these two greatly resemble one another, with the former lacking sternal plates, a retroverted pubis and caudal rods. These traits are also lacking in Eosinopteryx.
A relatively smaller skull – Much smaller than in Anchiornis.
A relatively longer torso – Much longer than in Anchiornis.
A relatively shorter pubis – Much shorter than in Anchiornis.
All these traits are primitive for theropods.
Huaxiagnathus was not included in the analysis of Godefroit et al. (2013). Neither were oviraptorids or alvarezsaurids. Eosinopteryx needs to be compared to these missing basal taxa along with the other taxa they previously tested. Once that’s done, let’s see if the topology of the tree doesn’t shift Eosinopteryx down below (more primitive than) Archaeopteryx.
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 somewhat as all pertinent taxa were included. Even so, I wonder why these two “sisters” don’t look more alike.
If anyone has details on why Godefroit et al. 2013 said the “bone structure would have limited its ability to flap its wings,” I’d like to see it.
Interesting that this birdy topic just came up a few days ago with Mahakala. Reminds me to be careful what I wish for.
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.