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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);
There is always an advantage in having the highest wingloading
commensurate with the ability to launch, land, and extract energy from
the atmosphere (if a soarer).
Good point. My main point is that maximum span versus mass
relationships may not have been the defining difference in max size
between birds and pterosaurs.
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.
The relationship in birds is actually a bit more complicated. Vultures
are large, but they're not that much larger by mass than the largest
seabirds (albatrosses) with high aspect ratios. Similarly, some of the
largest eagles have reasonably high aspect ratios (though the very
largest, being forest-dwelling taxa, have low aspect ratios). The very
largest flying birds by mass are swans and kori bustards. The former
have relatively high aspect ratio wings, while bustards have very low
aspect ratios (because they only fly for short distances at low
speeds). If anything, the situation is 'messy' enough that I probably
shouldn't have tried to make the comparison between chords in large
avians and large pterosaurs in the first place. I guess I had seabirds
on the brain at the time. Oh well, my mistake.
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.
True, it need not be unfavorable. I suppose I was mostly concerned
with the thresholds of being able to take off when I made that comment.
With regards to the trend, I probably underestimated the loadings in
pterosaurs. I really am much more familiar with the wing shape trends
in birds, after all.
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.
I have not done any calculations on that problem myself, but it
certainly sounds reasonable. Incidentally, any thoughts on the
apparent adaptations for dynamic soaring in Qspp given they show up in
terrestrial deposits? There are vultures somewhat adapted for burst
flapping, but they still use convective soaring most of the time. I'm
just forseeing problems with vertical wind shear gradients being too
low (unless they were actually coastal and just happened to die
...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
Thanks very much for the thoughts, I'm inclined to agree (I admit that
I've only just begun learning the mechanical implications of
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 soaring..
Also my take on the situation