Re: Science feather strength debate

[Tim Williams <tijawi@gmail.com>]

Erik Boehm <erikboehm07@yahoo.com> wrote:

> If you can power the downstroke, the upstroke (back to horizontal) should 
> take care of itself, what am I missing?


Apparently the humerus must be lifted above the horizontal in order to
achieve a recovery stroke.  This is according to Rayner (in the Ostrom
Symposium Volume) although this is not the only source.


> The presence of a keel, indicates the forelimbs were doing something that 
> required more power than could be delivered without the keel.


BTW, although _Confuciusornis sanctus_ (the type species) has a keel,
other confuciusornithids (such as _C. dui_, _Changchengornis_ and
_Eoconfuciusornis_) do not.


> When your forelimbs are elongated with small claws, but covered in long 
> aerodynamic feathers, and your descendants use the keel and forelimbs for 
> flapping, it
> seems simplest and logical to assume the most likely reason for the keel, was 
> flapping.


I take your point.  However, it now appears that many elements of the
flight apparatus arrived by a process of exaptation.  In other words,
they original had other (non-flight) functions, and took on a role in
flight.


Maybe the expanded pectoral muscles were used to help _Confuciusornis_
climb up tree trunks?  After all, the hindlimbs were poorly adapted
for climbing, so the forelimbs might have been forced to do most of
the work.


> If it had all these flight adaptation, but yet still was incapable of powered 
> flight.... what were those adaptations for? that seems like an awful lot of 
> adaptation for
> gliding between trees


That's assuming it glided between trees.  Maybe _Confuciusornis_
glided from trees down to the shore, or into shallow water?


Cheers

Tim