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Re: large fossil birds
----- Original Message -----
From: "Michael Habib" <firstname.lastname@example.org>
Sent: Monday, November 28, 2005 8:36 PM
Subject: 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
There is always an advantage in having the highest wingloading commensurate
with the ability to launch, land, and extract energy from the atmosphere (if
at least not by increasing span alone. Part of the issue might be a
relatively longer chord for giant pterosaurs (than in large birds),
Chord appears to have decreased relative to span in the larger azhdarchids.
Since the largest birds seem to have been rather low aspect ratio (like
vultures), I'd say that giant pterosaurs appear to have had a relatively
shorter chord than large birds.
resulting in a more favorable wing loading:mass scaling relationship.
That particular trend seems to me to have been in the other direction. But
I don't see that as necessarily unfavorable.
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
Azdarchids seem to me to have had adaptations associated with increased
power for burst flapping, not powered flight per se. They had quite high
aspect ratios (about 16.5 for Qsp and maybe roughly about 17.1 for Qn) and
appear to have been optimised for dynamic soaring rather than for convective
soaring. I doubt that they flapped for more than 15 to 30 beats at a time,
and would expect fewer beats most of the time.
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?
If by size you mean span, I wouldn't. Pterosaurs used a flight style that
doesn't require endothermy (though they do seem to me to be endothermic).
So they don't have to carry as much fuel load for a given span. They also
seem to have shifted more of the flight muscles from the torso out into the
inner half of the wings. Shifting weight into the wings is called
spanloading, and it greatly reduces the constraints on maximum wingspan.
Perhaps it was associated with the increased volume of the neck/head in some
of the azhdarchidae, as a compensating mechanism. I also suspect that birds
may have had structural and weight issues with feathers as they increased
the length and chord of the feathers and the loading upon them.
Pseudodontorns and teratorns reached spans and masses similar to very
Not quite so large as sternbergi.
Perhaps azhdarchids were simply doing something unique that birds haven't
I agree totally with that.
After all, birds include a wide variety of morphotypes/ecotypes that were
never seen in pterosaurs.
Which is, I think, why birds are still with us and pterosaurs aren't. If it
hadn't been for that big rock whacking us, I think pterosaurs would still be
with us, and birds might not have morphed to incorporate high aspect ratio