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Re: Large last gasp of pterosaurs




On Tue, 20 Jan 2004, James R. Cunningham wrote:
> > Definitely.  Inability to fly is an unlikely cause of extinction.
>
> I'd have to disagree rather strongly, in the case of the pterosaurs.  It
> seems likely that there was a period of several weeks at the boundary
> when conditions were unsuitable for soaring flight.  After that, voila
> -- no pterosaurs, but some continuously flapping birds survive.
> Flap-gliders don't.

Here is where I think circular thinking creeps in: Catastrophic mass
extinction is evidence of a hostile environment created by the
bolide-->pterosaurs became extinct at the same time so it must have been
because of the hostile environment.  I don't think you can have both be
evidence for each other, can you?

> If I were to guess at that, I'd say they didn't, though they mave well
> have provided selective pressure that drove the soaring pterosaurs
> toward larger sizes for two reasons.  1) There were no large, soaring
> birds at the time to compete for that niche.
> 2) Due to structural limitations, birds can't become as large as
> pterosaurs, so the large soaring niche will always remain preferentially
> available to the big pterosaurs, insolong as conditions remain
> continuously suitable for soaring.

This might be an ignorant question, but: how does any particular method of
flying enhance a bird's/pterosaur's competitive ability?  I understand
about vultures being able to stay aloft, and eagles diving on prey--but
how do you see this in relation to Q. and would-be bird
competitors/predators?

> I'm a little bit lost here.  For flying animals, size has little to
> nothing to do with range, for either birds or pterosaurs -- or
> butterflies for that matter.  Who increased their range, and why?

Albatrosses are large and have a large range, geese--I suppose I mean the
ability to stay aloft for a long time--w/out stopping.  Is this relevant
to Q.?

> I'm saying that all midsized to large pterosaurs were relatively immune
> to some causes of extinction that might apply to small pterosaurs.

Which causes?  Reproductive failure?  In extant species predation (in
birds, particularly during reproduction) is the primary limiting factor,
not head to head competition for food.

> > A pretty
> > good first order hypothesis is that were immune for a time because, like
> > modern albatrosses (for e.g.) they had extremely remote nesting places.
>
> Seems highly unlikely to me.  Why would they want remote nesting
> places?  However, I would expect them to travel about quite a bit for
> feeding purposes.  I do see them as migratory.

If you are big and cannot hide your nest very well, as well as being
somewhat limited in your terrestrial agility, you would want to distance
yourself from predators--this is especially true if you are migratory and
have the choice of remote/low predator density locations, e.g., geese,
albatrosses, penguins.

> > Again, I don't think size was important (necessarily, at least).
>
> We have a very different basic mindset.  I believe that you think birds
> were far more effective fliers than pterosaurs, and I see birds as less
> effective, at least till Diomedes exulans came along.  As I see it, your
> argument could just as easily be phrased the other way, with pterosaurs
> precluding the development of big birds.  I do see your point, I just
> don't accept it.

No.  I don't make such a clear distinction.  Birds and pterosaurs had
different strengths.  If you had an Olympic-games-of-flight, pterosaurs
would be stronger in some events and birds in others.  Perhaps birds were
more agile?  Pterosaurs better at soaring.  Whatever.  I think the real
problem for pterosaurs--if small/medium species became extinct
earlier--was their terrestrial existence--a relative ineffectiveness to
defend/protect/hide/locate nests for their progeny on the ground.

Of course I'm just guessing.  But the guess is informed by the problems
and amazing solutions supplied by extant birds.  I do feel that in an
Olympic games of nesting, birds would win.  This is not to say
that pterosaurs did not also have amazing abilities--just that birds may
have had the edge here.