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Re: Protungulatum index; pterosaur finger.
On Thu, 11 Jul 2002, James R. Cunningham wrote:
> ...trends in humerus shape in the largest azhdarchids appear to
> leave sufficent margin for substantial additional structural morphing
> to allow both more span and more weight.
I don't doubt it. But I was talking about structural constraints relating
to effective protection of their babies (about four posts ago).
> > .The pterosaurs appeared first in the field...but, by
> > Upper Cretaceous times, highly developed flying birds had been evolved;
> > competition with them may have been a factor in the elimination of
the l ast
> > of the pterosaurs."
> If b irds were so superior, why did large pterosaurs have to die off
> reall y large birds seem to have developed?
I would agree with you that pterosaurs may well have been superior in the
large flying category. The question is why this should have helped
pterosaurs compete? I mean, size in and of itself is not an adaptive
trait. Otherwise there would not be an intense selective pressure to keep
creatures small! I'm sure it is an advantage in a long distance
flier--but, if your large size means you are susceptible to other risks it
may be a complete liability.
> > If he is right about birds' abilities relative to pterosaurs',
> Is he right? The aerodynamic relationships that he seems to be
assuming make no
> sense to me.
He's talking about a competition where the stakes are absolute survival,
not who can fly the longest distance, or bear the strongest loads.
> > because feathers confer greater manueverability to creatures of equal size
> Wow. Why would anyone think that?
OK. This was the question I asked before I wanted to become involved in
such a discussion. Bats have a wing spread across most
fingers. Pterosaurs usually have a large part of the wing supported by a
single finger. As David mentioned, this gives bats wonderful aerial
manueverability. Well, what about feathers? Birds are the most agile
fliers we know; they have feathers; therefore feathers confer aerial
agility. That is why I think it.
> > -baby pterosaurs must be nurtured for longer than baby birds because
> > are heavier and develop less thrust than baby pterosaurs
> I 'm not sure what you were trying to say. Would you elaborate please?
What I'm wondering--guessing--is that there are significant diferences in
the time it takes to get feathered versus non-feathered first-time fliers
airborne. I know there are huge differences between bird species. Has
any work been done on this? Do large bat babies take off immediately
after birth as some birds do? David M. suggested this possibility for
pterosaurs. Could this hypo be supported by a finding of a precocial bat
> Hoplelessly clumsy pterosaur walkers--relative to nimble waiting
> Ha ve you ever manipulated articulated pterosaur wing and leg skeletons
> a walking cycle? I don't see anything clumsy about it. I don't think they
> woul d be all that effective at running, but then I don't see why they
> to be good at running anyway.
If they had to stay at the nest for extended periods of time--and those
nests were accessible to birds--they would be in a similar position to
that of the rhea. The rhea is constantly having to protect
its chicks by keeping the hawk at bay, i.e, striking at it. Ground speed
is relevant here. I mean, if we are not fighting in the air, ground speed
and agility must be relevant. My impression of pterosaur locomotion is
shaped somewhat by Walking with Dinos--is this a very bad thing?
> Aren't we assuming that pterosaurs are less effective in flight than birds
> without bothering to do the math necessary to prove it?
I am assuming only that pterosaurs were less agile fliers, not less
effective in other realms. Is there no math done on that already?