Re: large fossil birds

[Michael Habib <mhabib5@jhmi.edu>]

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.

Cheers!

--Mike


On Monday, November 28, 2005, at 07:32 PM, Patrick Norton wrote:

> From: "Tim Williams" <twilliams_alpha@hotmail.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.
>
> PTN