Re: Archaeopteryx

[larrys@zk3.dec.com]

>In the discussion about the evolution of flight, someone asked why 
>we don't see powered flight in squirrels.

>How do BATS fit into the picture, please?

It is fairly obvious that bats evolved from gliders based in
the trees or in rocky areas - but they did so a _long_ time
ago.  Bats have more species than any other mammal, a strong
indicator that they have been around for quite some time, so
it would be expected that they would be superbly adapted -
but the mechanisms of their flight - particularly that wing
membranes attachment point in the legs - shows an ancestry
that must be very similar to gliding squirrels today.  When
you look at one of the handful of gliding squirrels, you are
seeing the ancestral bat, another species discovering flight.
It will not take a huge leap of imagination to picture the
flying squirrels evolving longer fingers to increase the wing
area, nor the gradual integration of the digits into the wing
to provide better control.  It would be surprising if they
_didn't_ evolve flight - and I'm more than a little surprised
Dougal Dixon missed it in his "After Man" book speculating on
the future of evolution on this planet.

Archaeopteryx has too many characteristics of modern birds for
anyone to seriously doubt it could fly.  How well it could fly
will remain debatable until we can clone one and see.  Person-
ally, I think it mostly glided, reserving its strength and
flight muscles for bursts of powered flight to rise to a new
glide path or to another thermal, or to fly into a tree to
land.  And I think, especially after reviewing the whole dis-
cussion on this list, that cursorial flight development involves
too many seeming contradictions and leaps of faith when the tree
theory requires none, and provides a clear progression of evo-
lutionary advantages leading to powered flight.  It is certainly
a worthwhile exercise to speculate on alternative theories for
a particular feature, but it seems to be a fruitless endeavour
for Archaeopteryx.

On the subject of speculative evolution, though, it would be
nice to develop _some_ kind of cursorial flight hypothesis,
even if we _can't_ shoehorn Archaeopteryx into it.  It would
also be fun to wonder if flying fish might not eventually
evolve into true flying forms - but they will certainly need
adaptions to airbreathing, which may not be easily attained
in their bodyform.

regards,
Larry Smith