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Re: large fossil birds
The only catch is that azhdarchids didn't have particularly long wings
relative to their size. Thus, the issue does not seem to be one of
getting the wings large enough for the given weight (ie. maintaining a
low wing loading); at least not by increasing span alone. Part of the
issue might be a relatively longer chord for giant pterosaurs (than in
large birds), resulting in a more favorable wing loading:mass scaling
relationship. Again, however, I find this to be a dubious hypothesis
because azhdarchids didn't minimize wing loading and in fact have
several adaptations associated with increased use of powered flight
(rather than soaring).
Still, the ideas on wing weight constraints are quite intriguing. I'd
like to pose the following question, however (for the sake of
discussion if nothing else): Would we actually expect birds to reach
the same size as the largest pterosaurs? Pseudodontorns and teratorns
reached spans and masses similar to very large pterodontids. Perhaps
azhdarchids were simply doing something unique that birds haven't done.
After all, birds include a wide variety of morphotypes/ecotypes that
were never seen in pterosaurs.
Just some extra food for thought.
On Monday, November 28, 2005, at 07:32 PM, Patrick Norton wrote:
From: "Tim Williams" <email@example.com>
I wonder why...? Why couldn't birds get as large as the azhdarchids?
My personal theory about this is that maximum wingspan in birds was
constrained by the fusion of the carpometacarpus, which required the
elongation of primary flight feathers for the development of thrust.
Pterosaurs had no such hereditary mechanical constraint and were able
to extend wingspan by elongating the fourth finger. This was probably
a stronger mechanical arrangement for the outer part of the wing than
what evolved in birds, which at extreme sizes allowed for longer wings
that could develop more thrust to support more massive bodies.