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Re: Flight



 From: CORWIN3210@aol.com
 > 
 > But doesn't the paleogeology indicate that it did not live in a
 > forested area. And while that doesn't entirely eliminate the gliding theory,

It doesn't really even dent it.  Archaeopteryx had *already* evolved
flight - so it need not have lived in the same environment in which
flight actually evolved.  In fact, once flight has evolved, it can
very easily spread to new environments - since many things that are
barriers to ground-dwelers are are nothong at all to fliers.

 > I can't imagine the first avian ancestor falling out of a tree, flapping its
 > arms wildly, and plummeting a'la Wile E. Coyote.

Try *jumping* from one branch to another - like a squirrel.
Now, add a small flap that allows slightly longer jumps ...

This is *certainly* how the flying squirrels evolved, and the
flying lemurs, and the various gliding lizards.  It is also
likely the way that bats got started - from tree shrews, or
something similar.

 > So perhaps archaeopteryx may have developed flight from the ground up,
 > running along and leaping into the air, gliding, and catching more and more
 > insects. This idea doesn't make sense to me. 

If you work out the dynamics in a little more detail, and remember
to try to find other animals that have a similar life style to
your proposed intermediates (to demonstrate that such an animal
really is viable) I think you will find that there are even more
serious gaps in this model than you suggest.

1. the sort of arm movements used to capture insects are *very*
   different than the sort used to fly (the direction of motion,
   the rythm, and the nature of the stresses are very different).

2. The force needed (or even useful) for catching insects is *far*
   short of the force necessary to achieve lift.  (In research on
   the origin of insect flight the demonstration that the proto-
   wings improve in their non-flight functions all the way up to
   the point where flight is possible is considered a critical
   necessary criterion)

 > Why wouldn't archaeopteryx (and its close ancestors) have a lifestyle similar
 > to that of other small theropods? 

At first, certainly they did.  But in order to explain the evolution
of flight, it is necessary that they switched to a different life-
style in *some* way.

 > And if it did share that lifestyle, what
 > advantage is there in flight?

Wrong question.  It is impossible to get from a typical theropod
to flight in one step.  Typical theropods simply lack the necessary
physical structures.

The *correct* question is: what advantage is there in the proposed
proto-wings that could allow them to evolve to a size and strength
sufficient for flight to be possible?

Once flight is *possible* its advantages are clear - escape from
predators, larger home ranges (for locating food), the possibility
of putting helpless young in less accessible places, and so on.

The problem is getting there from the starting point.  *All* of
the intemediates must be viable animals, and the major changes
should probably have some immediate adaptive advantage in *some*
environment.


So far, only the arboreal jumper model is really supported in
the sense of involving only forms known to be vialbe from other
analogues.

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

The peace of God be with you.