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Re: pterosaurs, bats, flying theropods



Let's see if I can beat Jaime's response this time... Michael, after this
message, the listprocessor should recognize you again.

---------- Forwarded message ----------
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<


Seems very likely to me as well, given that diurnal habits are
plesiomorphic for birds and nocturnal habits are plesiomorphic for
bats.  Bats do probably have a strong advantage at night, and birds do
seem to have an advantage during the day.  Yes, there are nocturnal
birds and diurnal bats, but the relative proportions are very small.

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).

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...

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

Given the timing, it seems that microbats really do have some
advantage over birds at night (ie. Birds did not move into the
nocturnal activity cycle in large numbers, even without bats, but bats
did in the presence of birds).  Birds might have a competitive
advantage during the day, or it could just be an exclusion phenomenon.


>Oh, molecules are not miraculous, and it does depend on theories of
genetic change having a morphological expression, and how much a set
of genes can express such. Most molecular dates do not take into
account the possibility of Eldredge and Gould's PE, for example, or
that gene evolution may occur at different rates with constraints at
different times in a single lineage<

Well, naturally they're not 'miraculous', but different methods do
consistently place Chiropteran orgins before the K/T boundary.  One
can recalculate local clocks within a tree, using a strong ML model,
to help correct for the differences.  Also keep in mind that the
Chiropteran flight apparatus appears in advanced form at about 55 mya.
 It seems to me there is no reason to assume, at the moment, whether
bats appear before or after the K/T.

--Mike Habib