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Re: flapping from gliding



Stan Friesen writes (quoting me):

> > Besides, pterosaurs must have descended from walkers/runners, not gliders.
 
> Oh?  On what grounds?

On the grounds that when you look at the earliest known pterosaurs,
they seem to be adapted for running/walking, and not climbing.
_Preondactylus_, probably the very earliest known pterosaur,
 had rather long legs, in fact the longest of any pterosaur.
It could stand upright, and seems to have been at least a fast
walker/hopper if not runner.  It also has the shortest wings of
any pterosaur, confirming its status as a very primitive pterosaur.

_Dimorphodon_, another very early pterosaur, was clearly a agile runner.
(for a thorough analysis of this, see:
 Padian, K., "The Flight of Pterosaurs", Natural History, December 1988)
 
I will admit that intuitively it seems like flying is a small step
from gliding.  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. 
("climbing" defined as using your hands to assist in ascending;
sure, birds can sometimes walk up a tree using only their legs).

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.)  But the transition:

        aboreal gliding -> flying

is not plausible.  This explains why, of the many known animal gliders
(flying squirrel, flying snake, flying fish, flying squid, etc.),
none of them has ever evolved powered flight, even after millions
of years of evolution.

-----------
Achut Reddy                     So many fossils... so little time!
achut@troodon.isp.net