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Re: flying Archie

An alternative "bottleneck" evolutionary path to the gradual terrestrial 
transition scenario; abandonment of terrestrial locomotion entirely 
(perhaps/probably for an aquatic environment), and then after the avian 
bodystyle was well-established, re-invasion of the terrestrial environment. 
Flight superiority well in wing, so to speak. No worries about center-of-mass 
issues relative to the hindlimbs during "remodeling" there.


----- Original Message ----
From: Tim Williams <twilliams_alpha@hotmail.com>
To: dinosaur@usc.edu
Sent: Sunday, September 24, 2006 1:44:16 PM
Subject: Re: flying Archie

In basal birds (including _Archaeopteryx_), predator avoidance (or evasion) 
could have been achieved in the old-fashioned way: Running away.  The thing 
about a long bony tail is that it does help keep the center of mass 
posteriorly, whereas shortening the tail (and expanding the sternum and 
pectoral musculature) shifts the center of mass forward of the hips.  Modern 
birds have had to do a complete 'makeover' of the hindlimb in order to 
locomote on the ground, with stride generation principally occuring at the 
distal femur, not the hip.

I don't know at what stage the femur was decoupled from stride generation in 
avian evolution, but there must have been a transitional phase from the 
primitive theropod style to the derived avian style.  During this 
transition, running on the ground might have been difficult, and birds may 
not have yet reached the point where a vertical takeoff was do-able.  This 
could have been one selective pressure that kept _Archaeopteryx_ in its 
plesiomorphic coleurosaurian body plan.  There are "costs" associated with 
the modern avian body plan, and I suspect Archie represents a compromise: it 
kept the benefits of a coelurosaurian osteology (including the primitive 
terrestrial locomotor style), while the plumage became dedicated to aerial 

Don Ohmes wrote:

>Not local eco-stuff... also, implied in your post is the idea that A. may 
>have been more optimal for tree to tree flight than modern birds, and birds 
>sacrificed that to obtain long-distance flight. Highly doubtful, right?

I personally don't believe that _Archaeopteryx_ was optimal for tree-to-tree 
flight.  The reason I say this is that its perching abilities were minimal 
to nonexistent.  However, I do believe that _Archaeopteryx_ was adapted for 
flying over short distances.

Heinz Peter Bredow wrote:

>I think that this concentration on Archaeopteryx regarding the origin of 
>flight is arbitrary.

I don't think it is.  Chronologically and morphologically, _Archaeopteryx_ 
is the first known theropod to show evidence of powered flight.  Thus, until 
we have evidence to the contrary, then we must assume that _Archaeopteryx_ 
at least approximates an early stage in the evolution of flight.  It 
certainly may not have been directly ancestral to later birds; and I don't 
deny that it is possible that _Archaeopteryx_ is a bizarre aberrant form 
that is a complete red herring to avian evolution (as you suggest).  But the 
latter implies that we know a *lot* less than we think we do about avian 
evolution, which is a sobering thought.