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Re: Arms into wings
>However, you are suggesting that the pattern is: grasping -> ??unknown?? ->
>flying. In fact, what the morphological studies of _Archaeopteryx_ and
>_Confuciusornis_ hands suggest instead is: grasping -> grasping + flying ->
>flying only (with the "handy birds" Archie & _Confuciusornis_ representing
>the middle stage).
Oh no - I understand that the earliest birds (like Archie &
_Confuciusornis_) used their wings for BOTH grasping and flying.
Later/other avian lineages dispensed with the grasping bit. However, in
some pre-_Archaeopteryx_ stage the forelimb must have gone through a
grasping + ??unknown?? stage, and this ??unknown?? was the seed that gave
rise to flying.
And, as you say (and as Ostrom has been saying for decades), this all
happened with very little (if any) change to the forelimb skeleton. What
exactly happened (or what you believe may have happened) with the feathers
depends upon what scenario you favor.
>(Actually, the above scenario would fit in with Greg Paul's scenario, with
>Archie representing a grasping + flying stage and dromaeosaurids etc. being
>descendants of Archie-like forms in which the grasping ability was
>maintained but the flight ability was lost.
On the face of it (and pushing cladistic analyses aside), the scenario is
rather attractive. For example, the feathers of _Caudipteryx_ and
_Protarchaeopteryx_ have symmetrical vanes. Based upon the phylogenetic
position of these critters (particularly _Caudi_ as a possible
oviraptorosaur), the symmetrical feathers came first and gave rise to the
asymmetrical feathers used by _Archaeopteryx_ and other birds to fly. But
what's the use of symmetrical feathers? It could be that _Protarchae_ and
_Caudi_ are secondarily flightless, and that the symmetrical feathers
evolved from asymmetrical, flight-giving feathers. The asymmetrical
feathers necessary for flight evolved via another route.
Or - the symmetrically-vaned feathers were useful for short, fluttering
"hops" off the ground. In which case the symmetrical feathers came first.
I'm not very knowledgeable on the functional morphology of feathers so I
won't push this one too far.
I wonder what would happen if all flight-related skeletal characters were
coded as one in cladistic analyses. When birds lose their ability to fly,
more than one character may revert to the "primitive" condition (shorter
arms, longer legs, reduction of sternum, loss of keel). If certain
flightless theropods are descendents of primitive flying birds, then
distinguishing genuinely primitive states from secondary loss of
flight-associated characters could be tricky. I don't envy you
number-crunching cladistic analysts! ;-)