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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
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.

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,
no?

> 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).