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Re: Protungulatum index; pterosaur finger.



Interesting opinions here.  Some comments inserted below.
JimC

John Bois wrote:

> > > Bois said about pterosaurs:
> > > >> Here you may be up against absolute limits in structural design.  Come
> > to think of it, good reason to go extinct.
> > > >
> > > > Then please suggest some structural constraints.

Er, uh -- 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.  It may be that we haven't seen the largest pterosaur
fossils yet.  The biggest ones I've seen don't seem to me to be particularly
close to the limits for pterosaur flight, and I'm looking at one of the larger
ones (a northropi humerus cast) as I write this.

> Quoting Romer: "It seems obvious that (pterosaurs) were not so well adapted
> for (flying) as birds..

Again, er uh.  Why is it that the largest known pterosaurs were 50% greater in
span than the largest known birds?  Is it because they were not so well adapted
as the big birds, or just because the big birds weren't adapted well enough to
reach that size?  And why do the biggest pterosaurs appear to have lift/drag
ratios unmatched by most everything but a few albatrosses and Frigate Birds (and
I'm not sure about Frigate Birds).  It doesn't seem so obvious to me that birds
were better adapted near the end of the Cretaceous than pterosaurs.  How many
large, soaring birds were around then?  And how did their size compare with that
of the latest pterosaurs?

> .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 last
> of the pterosaurs."

If birds were so superior, why did large pterosaurs have to die off before
really large birds seem to have developed?

>  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.

> because feathers confer greater manueverability to creatures of equal size

Wow.  Why would anyone think that?

> -large flying pterosaurs would be sitting ducks.  Falconiforms drop on them
> from on high, etc., etc.

With their greater wing loading, why wouldn't the large flying pterosaurs just
outcruise the Falconiforms after the first dive?  Note that I'm not saying that
they did, or that they even needed to.

> - just as bats are banished (largely) from the day niche by birds, the even
> less effective pterosaur fliers would be prey to Cretaceous equivalents

Since large pterosaurs appear to have been more effective flyers than large
birds, how much water does this argument hold?

> -baby pterosaurs must be nurtured for longer than baby birds because they
> are heavier and develop less thrust than baby pterosaurs

I'm not sure what you were trying to say.  Would you elaborate please?

> Hoplelessly clumsy pterosaur walkers--relative to nimble waiting fliers,

Have you ever manipulated articulated pterosaur wing  and leg skeletons through
a walking cycle?  I don't see anything clumsy about it.  I don't think they
would be all that effective at running, but then I don't see why they would need
to be good at running anyway.

> at least--must watch their babies more carefully.  More PI
> needed...therefore they are less competitive.

Somehow I failed to pick up on why more PI is needed, so I guess I failed to
pick up on their being less competitive as well.  Is it possible that
atmospheric conditions near (but before) the end of the Cretaceous were more
conducive to large soarers than to small soarers?  Could this have anything to
do with the seeming trend in pterosaur size toward the end of the Cretaceous?
Aren't we assuming that pterosaurs are less effective in flight than birds
without bothering to do the math necessary to prove it?

All the best,
Jim