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Re: Protungulatum index; pterosaur finger.

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Thursday, July 11, 2002 10:05 PM

> 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?

It should have helped them avoid competition -- that way they were able to
occupy niches that were totally denied to any (known) bird of that time.

> 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!

Is there one? I mean, there is a selective pressure that keeps shrews small.
Apparently there was another selective pressure that kept sauropods big.
What keeps insects small is not a selective pressure but a structural
constraint. A general intense selective pressure against big size?

> > > 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.

I can't see how this doesn't relate to Romer's quote.

> > > because feathers confer greater manueverability to creatures of equal
> >
> > 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.

I didn't say the fingers did that. I said the cambered wing does that.
Source: DA.

> 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.

Firstly, if correct, this would be statistics with a sample of 1. Secondly,
if "agile" and "maneuverable" is something similar, then bats should be more
agile, at least the average bat should be more agile than the average bird,

> 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.

Why do you wonder in the first place? What reason could there be?

> Do large bat babies take off immediately
> after birth as some birds do?

Don't think there are any -- like most placentals bats are rather altricial
as young. Besides, those birds that do take off some hours after hatching
are the megapodes that have never seen their parents.

> David M. suggested this possibility for
> pterosaurs.

Possibility... phew. Very, very wild speculation. There's just no evidence
against it at the moment. :-)

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

But what if they nested, say, in colonies on tiny islands? Then the
situation is totally different than that of a rhea in the endless pampas.

> 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.

Maybe only neck speed is relevant. I don't know what rheas do, but I can
imagine an azhdarchid sitting on its nest and completely covering it, saying
"not over my dead body" to everyone interested in eggs.

> I mean, if we are not fighting in the air, ground speed
> and agility must be relevant.

Maybe size is enough, see above.

> My impression of pterosaur locomotion is
> shaped somewhat by Walking with Dinos--is this a very bad thing?

Maybe not very, but they did make them more clumsy than they were. The maker
of *Pteraichnus* held its wings as vertically as its legs (same gauge).