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Ad Explanorum Origam



Tim Williams wrote:

<<It's like that bugbear of an argument that flight in
birds probably evolved in an arboreal ancestor because
it is "easier" to evolve flight from the trees down
than the ground up.>>

<Not just "easier." I think the physics of the
situation >completely precludes< evolution of flight
"ground up" invertebrates. Energy to remain aloft
without already having well-developed, flightworthy
wings is simply not there. This falsifies the ground
up hypothesis; drives a stake through its heart.>

  Now this is an hypothesis. A good one, too. But
we're talking about two different explanations. Origin
of birds is separate, possibly, from origin of flight.
The hypothesis is that they are directly linked, and
this must be demonstrated. Physics suggest that an
animal in the trees will have an easier time of
getting _through_ a gaseous medium than a terrestrial
animal to attain the same point in space, if they are
both the same in evolutionary development. Take a time
machine, go to Solnhofen, and watch an Archie in a
tree (okay, imagine here for a moment there _was_ a
tree, just a point of explanation) as opposed to an
Archie on the ground, and both would, as has been
demonstrated by Burgers and Chiappe (1999), Chatterjee
(1992, 1993, 1995, 1999), Feduccia (1997, 1999), even
Zhou et al. (1995, 1999) that both animals will be
able to get into the same point in the air. They can
do it from the tree, or from the ground. Physics does
not preclude this condition. Not with the known fossil
record, anyway.

  Now, take a hypothetical more basal aviform
creature, and we can only think that there was some
condition that may or may not preclude aerial
ascension from a tree, or from the ground. This is
speculation (I'm not accussing anybody, by the way,
I've heard many people say this, even here in Idaho --
no potato jokes!), and cannot be established in either
a test or as a theory without generating a fictitious
model. Now, you _can_ develope a fictitious model, a
series of intermediates from one form to, say, an
Archie body plan, and perform the tests Burgers and
Chiappe and others have done on Archie, and see
whether the physics would allow ascension from the
ground, or preclude it.

  So, hypothesis: Early bird evolution of flight was
from an arboreal (i.e., "trees down") model, rather
than a terrestrial (i.e., "ground up") model.

  Test: morphological series to determine capability
of flight from either the ground, or from the trees,
compute efficiency, compare models with fossil forms
to find "best match" animals, hypothesize likelyhood
of form in origin of flight (from tree, from ground),
repeat tests.

  Present.

------

  One thing about *Longisquama* that apparently has
not been looked at is the capability of the
structures, if indeed they are homogenous, to actually
keep the animal in the air, hypothesizing they could
increase ventral air pressure in the first place. All
gliding animals (kuehneosaurs, *Draco*, flying fish,
flying snakes, gliding rodents and flying lemurs, and
bats) have a continuous dermal "sail", rather than a
structure composed of multiple flaps or "fronds";
birds do, but these very significantly overlap even in
full extension except at the tips of wings and tails,
where the whole still creates air pressure effective
enough to keep the animal _up_. Could any of you bird
or aeronautic specialist out there do some quickie
calcs for us?


=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
Check back soon.

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