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Re: Senter 2006, Confuciusornis, and humeral mobility



On Wed, Mar 23, 2011 at 7:53 AM, Jason Brougham <jaseb@amnh.org> wrote:

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

Agreed.  For basal birds, up to and including confuciusornithids,
there is no reason to *assume* that they were powered fliers.  The
idea is intuitively attractive, and fits with the fact they look like
modern birds - which goes to Scott's point about calling these
critters "birds" gives rise to assumptions about behavior.  But if you
scratch beneath the surface, the evidence for powered flight is
ambiguous.


> 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).

Only two _Confusiusornis_ specimens show an "incipient keel" - and
even here it's nothing more than a shallow ridge:

http://dml.cmnh.org/2010Nov/msg00025.html

Most of those other characters (small body, huge arms, pygostyle, big
sternum) have a checkered distribution among derived maniraptorans -
both avialan and non-avialan.  Sure, these flight-related characters
come together in pygostylian birds, including confuciusornithids.  But
individually, these characters might have originally evolved for
purposes unrelated to powered flight.  This is why I'm hesitant to
refer to any of these characters as "flight-related", either
collectively or individually.


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

_Baryonyx_ also had a fish in its tummy.  Also, only one
_Confusiornis_ specimen among hundreds preserves fish remains among
its gut contents.




Cheers

Tim