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Re: flapping from gliding



From: achut.reddy@Eng.Sun.COM (Achut Reddy)

 > On the grounds that when you look at the earliest known pterosaurs,
 > they seem to be adapted for running/walking, and not climbing.

How about them being an animal that is adapted for both?
[Such as leopards and cats are today, not to mention squirrels].

The front leg structure is what is significant for climbing, and
that seems to be well adapted for that in all pterosaurs I know of.

 > But if you mean arboreal gliders, then there is a
 > fatal flaw in the argument.  Namely, arms adapted for climbing are
 > incompatible with arms adapted for flying.  So, while there can
 > be climbing gliders, there cannot be climbing flyers. 

You should check out the hoatzin - it is, as a juvenile, both a climber
and a flyer.

And, more to the point, the arm structure of Archaeopteryx seem to
me to be well adapted for climbing as well as for flying.

For that matter I would like to see where the descendents of the
Madagascar sifakas have gotten to in 20 million years. Since they
habitually jump long distance between trees, they seem to be prime
candidates for airfoils.  Furthermore, given their unusually long
arms, such airfoils are likely to be developed mostly from the arms,
instead of between the arms and legs as in flying squirrels.

 > If you want to argue for a transition like:
 > 
 >      running -> running/gliding -> running/flying -> flying
 > 
 > then at least that would be more plausible.  (By running/gliding
 > I mean something like what you see people do who are learning 
 > how to hang-glide.) 

The problem I see with this is that I can see no way for the proto-
wings to evolve to the point that the exaption to gliding could occur
under this model. (See my previous letter for more details of this).

Maybe the sequence:
        arboreal => arborealglider => running/glider => flyer
would work.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.