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Re: Ad Explanorum Origam
If birds and petrosaurs evolved from arboreal archosaurs (I think it's very
probable), where were these arboreal groups? Flying and gliding mammals
evolved from arboreal mammals, and squirrels, possums and primates have many
species around the world. And about arboreal dinosaurs or archosaurs? Maybe
they be in front of our eyes and we can't see them.
----- Original Message -----
From: Jaime A. Headden <firstname.lastname@example.org>
To: Index Dinosauricus <email@example.com>
Cc: <Dinogeorge@aol.com>; <firstname.lastname@example.org>
Sent: Friday, June 09, 2000 5:08 AM
Subject: 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.
> 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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