Re: Confuciusornis sanctus

["Patrick Norton" <ptnorton@email.msn.com>]

>C. sanctus has very small feet, but large talons on its hands.  Does this
indicate that it used its hands to perch <

Dan,

I think that once feathered dinosaurs got into the air, aerodynamics became
the primary selective agent on wing design, including fingers and claws.

>From that perspective, the hand of _C_ could be seen as an example of an
early stage in the evolution of the carpometacarpus.  While digits I and III
on _C_ were relatively large with well developed claws, digit II--the finger
to which the flight feathers were attached--is described as having
differently shaped bones ("flatter" is the word I recall) and a reduced
claw.  It may have been able to grasp with its hand, but my bet is that it
was not a very good at it because of the flight related modifications of
digit II.

So if the claws weren't used for prey capture or grasping, what was their
function?  I've often said that, prior to the evolution of the
carpometacarpus, the hand claws of flying dinosaurs served a very important
aerodynamic function---similar to that of the feathered alula seen in more
derived feathered flyers.  Elevating and extending the manus claws during
slow flight would have created turbulence across the upper wing surface,
decreasing the stalling speed for _C_ and allowing it to maintain better
control at slow speeds.  The alula of more derived birds is an example of
feathers being exapted to maintain those functions as other aerodynamic
demands acted on reducing the fingers and claws even further.

I would really like to see some wind tunnel work testing how the claws and
unfused fingers in the wings of early flying birds performed
aerodynamically.  Maybe someday.

Pat