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Re: Senter 2006, Confuciusornis, and humeral mobility



Hi Scott,

Powered flight must not be the null hypothesis, and I have an open mind. I've 
said before that gliding is plausible.

But you are right if you think I am biased towards powered flight for 
Confuciusornis.

My reasons include:

The overall anatomy of the animal: the small body, short legs, huge arms, strut 
like coracoid, pygostyle, and big sternum with incipient keel, are thought to 
correlate with flight ability (Chiappe et al. 1999).

At least half of the specimens lack aerodynamic tail feathers, which suggests 
that any aerodynamic capabilities would be unstable, advanced, types rather 
than gliding which would probably benefit from  a good stabilizer (like the 
long tail of Archaeopteryx).

The fish found in the crop of one specimen (though it could have been carrion 
found on the beach)

Now, the new evidence from Wang, Nudds, and Dyke that the arm length to primary 
feather length ratio groups with ornithurines, and does not overlap with more 
primitive birds.

> The thing is that given the orientation of the glenoid and the
> supracoracoideus it can't stabilize the arm in the socket of
> Confuciousornis; modern birds (even with a cut supracoracoideus) still
> have the modern glenoid orientation, which provides better bracing to
> the humerus during flapping motion.  

Please explain. How does the modern glenoid brace a moving humeral head when 
the supracoracoideus is cut?

I too prefer to restrict Aves to the crown group, but I'm cooler with calling, 
say, enantiornithines birds since the latter is an informal term.

It is hard to be convinced by the impressions of anatomists, because they so 
often disagree about function. Hou, Chiappe, Clarke, and Norell have looked at 
the pectoral anatomy and favored powered flight. Anatomists like Senter and 
yourself have looked and favored gliding. I have never closely examined  a 
fossil of Confuciusornis myself. 

I think that you and I might agree that the real problem is designing 
experiments to test the functional hypotheses.

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544