And now Dave, the Sinornithosaurus, leaves the ‘raptors’

Revised December 27, 2015 with extended scapulae on both the tracing and reconstruction.

Yes, I know it has feathers
And yes, it has a tail stiffened with elongated processes.
And yes, it has long ‘raptor’ fingers.
And yes, it could have had a posteriorly-oriented pubis.
And it had relatively shorter hind limbs.

I was really hoping
this one would pull the other micro- aptors back to raptor-ville.

Figure 1. Sinornithosaurus ("Dave", NGMC 91) shown as plate and DGS tracing.

Figure 1. Sinornithosaurus (“Dave”, NGMC 91) shown as plate and DGS tracing.

Even so…
the present (and always provisional) suite of character traits currently attributed to ‘Dave’, the Sinornithosaurus (NGMC 91, Ji et al. 2001) nests it (Fig. 3.) with Microraptor (in the large reptile tree at 619 taxa) which nests with Compsognathus and Tianyuraptor + Zhenyuanlong + Tyrannosaurus. Not Velociraptor.

Figure 2. Reconstruction of Sinornithosaurus based on DGS tracing of figure 1. Note the oddly small scapula and coracoid. Ribs and gastralia were omitted from the lateral view.

Figure 2. Reconstruction of Sinornithosaurus based on DGS tracing of figure 1. Note the oddly small coracoid. Ribs and gastralia were omitted from the lateral view.

You know,
sometimes you just have to go where the data takes you.

Figure 3. Theropod subset of the large reptile tree showing the nesting of Sinornithosaurus.

Figure 3. Theropod subset of the large reptile tree showing the nesting of Sinornithosaurus.

Some interesting things happen
when you play deletion games. For instance, delete the four taxa closest to Sinornithosaurus and there’s a shift in tree topology. T-rex nests between Sinocalliopteryx + Allosaurus and Compsognathus, which nests basal to Sinornithosaurus, and the rest of the tree is the same. The re-insertion of any one of the deleted taxa does not repair the tree other than Tianyuraptor, which alone restores the topology.

And finally, a little about Sinornithosaurus
I note oddly small coracoids here. While the coracoid is elongated, it is also much smaller, probably due to a reduction in flapping capabilities. The so-called ‘killer’ toe claw (#2) is long and gracile, not what you might call robust. Perhaps ideal for perching, but pedal digit 1 is also oddly tiny. The specimen appears to have smaller wing feathers than in Microraptor, it’s provisional ancestor sister. It also has shorter teeth and a down-tipped premaxilla.

References
Ji Q, Norell MA, Gao KQ, Ji S-A and Ren D 2001. The distribution of integumentary structures in a feathered dinosaurs. Nature, 410(6832): 1084-1087.

wiki/Sinornithosaurus

 

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