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Re: mammal mystery



From: John Bois <jbois@umd5.umd.edu>
 >  Rails are not flightless are they.  They can fly
 > away from a low to the ground predator.  Surely if they were as "good"
 > as the others in this niche they would lose their wings.  After all,
 > it is expensive to fly (I claim this is demonstrated by the apparent
 > rapidity with which flightlessness occurs on predatorless island
 > species).

I think there may be other factors at work here.

On possiblity is the risk of being blown out to sea in a strong
wind if one is flying.  This could add an extra level of selection
against flight on small islands.

If this is valid, then the rest of your argument is invalid.
[I know, this needs to be verified].

 > Further, I say that the four legs are better at getting through what
 > must be, in a tangled thicket, a series of hoops.

Then you haven't seen a brown thrasher either.  They are very nimble
in the underbrush.  They are also, like rails, difficult to see.
Yet they only fly when threatened.  This is not their normal mode
of locomotion.

 >  It means landing on your
 > feet instead of your beak.  Otherwise, how to explain the great lack of
 > bipeds (without wings, now, since wings provide means
 > of escape) in the tangled thickets?
 > 
Easy - mammals are predisposed to quadrupedal locomotion, and generally
are unable to evolve bipedal forms.  Only a two rather unusual lineages,
kangaroos and anthropoid primates, have evolved quadrupedality.  And
in the antrhropoids, at least, I can make a case that this is due to
secondary terrestriality in arboreal *brachiators* (not merely normal
arboreal forms).

On the other hand archosaurs are/were predisposed to bipedality due
to their limb structure, so they evolved it several times.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.