Eosinopteryx – part 3 – to scale

Sometimes it just helps
to see taxa to scale with possible sisters (Eosinopteryx in this case, Fig. 1). Smaller than Anchiornis, Eosinopteryx also had a shorter snout, deeper mandible, more robust postorbital, longer torso, shorter tail, larger chevrons, more robust clavicle, coracoid and scapula, shorter forelimb, smaller deltopectoral crest and shorter pubis.

Huaxiangnathus shared with Eosinopteryx a short coracoid, but little else is a closer match than the similarly built Anchiornis. Godefroit et al. (2013) reported, “The straight and closely aligned ulna-radius of Eosinopteryx also means that pronation/supination of the manus with respect to the upper arm would have been limited; combined with the absence of a bony sternum and weakly developed proximal humerus, these attributes suggest that Eosinopteryx had little or no ability to oscillate the arms to produce a wing beat.”

Funny that they didn’t even mention the short coracoid.
The locked down elongate coracoid is a hallmark of flapping tetrapods (pterosaurs and birds) and an elongate clavicle does the same thing in bats.

According to the Sinkkonen illustration (Fig. 1), the radius and ulna are likewise essentially straight in Anchiornis, which is the plesiomorphic condition, as shown by Huaxiagnathus and other theropods. The ulna is barely bowed in Archaeopteryx and more greatly bowed in subsequent flapping taxa, including oviraptorids (by convergence?). Xiaotingia (Fig. 2), the outgroup to Anchiornis + Eosinopteryx, also has a short rostrum, but also a greatly bowed anterbrachium and a locked-down coracoid. I suspect a change in tree topology may be warranted or else we’ll learn something here about reversals.

I have asked for the matrix.

The bowed antebrachium
produces a parallelogram in living birds that serves to automatically extend and fold the manus bearing the outer flight feathers with flexion/extension of the elbow. Prior to this, muscle power would have to extend and bend the wrist, independent of the flexion/extension of the elbow.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
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

wiki/Eosinopteryx