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Re: pterosaurs, bats, flying theropods (fwd)



> From: Michael Habib <mbh3q@cms.mail.virginia.edu>
> To: dinosaur@usc.edu
> Date: Tue, 24 Dec 2002 16:01:12 -0500
> Subject: Re: pterosaurs, bats, flying theropods
>
> >If one body plan (birds) dominates the diurnal niche to the
> extent birds do, we must admit this is not just a matter of chance:
> birds have it over microbats in the day time<
>
> > What about another idea: birds were already there in the daytime,
> and, in order to _avoid_ competition, most microbats stayed nocturnal<

Except that, if http://www.cmnh.org/dinoarch/1996Aug/msg00050.html is
correct, bats were there first--and were happy in the diurnal niche until
nasty raptors came along.

> Bats do probably have a strong advantage at night, and birds do
> seem to have an advantage during the day.

True.  But to what does each owe this advantage--not to foraging ability,
but to predation avoidance or lack of it.  This is what the evidence seems
to suggest.

> The thing is, placentals have been, and still are, essentially 'small
> brown things': small-bodied, nocturnal endotherms.  They're fantastic
> at it.  Most mammals still fall into this category (after all, extant
> Mammalia is basically made up of rodents, bats, insectivores and misc.
> taxa).  The ability to hear high-frequency sounds appeared early in
> the mammalia; this is good for moving at night, and even better if it
> can be adapted as a navigational system (ie. microbats).

Yes.  These remarkable abilities gave them a margin for existence.

> Basal birds were probably visually-based diurnal animals, and extant
> birds still are, for the most part.  Great color vision, lots of
> high-speed flyers...

Maybe speed is the thing--a raptor swooping on a flock (right word?) of
bats.

> Of course, differences in flight might be responses to the differences
> in active photoperiods, not the other way around.

Well, a creature needs to move faster in the daylight when the predator can
see it.