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Re: Speed Potential in Tyrannosaurs (long)



Greg Paul (GSP1954@aol.com) wrote:

<Hutchinson and Garcia?s paper on speed potential in tyrannosaurs in
Nature garnered widespread attention and considerable approval. This
summer I and others (Christiansen, and Blanco & Mazetta) sent three
separate replies to Nature, all were rejected. The replies of leading
researchers into speed potential of giant avepods(see Paul 2002) which
expose critical flaws in H&G?s study will therefore not receive proper
attention in the near future.>

  I think this is a sociopolitical comment that could use corroboration,
Paul.

<I am working with others to produce an extensive study into the
locomotion of giant avepods, which will take substantial time to appear.
My Nature reply with some alterations is below, followed by further
discussion (which is largely limited to factors pertinent to the H&G
study, this is not a comprehensive analysis of all aspects of the issue).
I and Guy Leahy will also present a poster on the subject at the SVP
meeting.>

  Howe much of the remainder of this post was the reply to Hutchinson and
Garcia? I can see two flaws with why the remainder of Paul's post were not
published, as he kindly provides us. The first is that the following
paragraph makes a few statements that are not supported in itself. In a
reply to _Nature_, or commentary in _Science_, the format is to present a
brief concourse on _why_ you disagree. Simply saying that an implication
(your observation) is different or observation is not evidence.

  "The zones in their Fig. 3 imply that running potential decreases as
   leg extensors become a larger percentage of body mass when the oppo-
   site is true (the correct question is what is the maximum portion of
   total mass that can be dedicated to leg extensors),"

Similar is that statement about incorrect prediction of juvenile
tyrannosaur locomotory performance.

  "The failure to correctly model even a small tyrannosaur falsifies
   their results..."

  Previously, the argument was "similar-sized ostrich" ran in a different
trajectory. The authors estimate muscle mass not from size of the animal
(and ostriches have gigantic hindlegs, proportionate to their total body
mass much higher than in any theropod dinosaur, as is true of most running
birds) but from scar sites and long bone circumference and, as the
author's state and John provided onlist discussion to, modelling of
muscle-site anchors, moments, etc. This method has not been tried before
for any theropod or bird within them, and can hardly be criticized by
methods which do not consider the evidence forward.

  The second issue is that the remainder of the post is much too extensive
for a reply, otherwise the reply is a single paragraph within one only
criticizes previous evidence, but does not show HOW it is falsely derived
by providing an alternate concept. I cannot say, for instance, that Bakker
falsely derives the nature of *Denversaurus* because it's an *Edmontonia*
skull, and probably *E. longiceps*; this is unsound, because no data is
present, only an opinion. I think the bulk of this reply should not have
been sent to _Nature_ as a reply, but perhaps instead to another journal
as a discussion of alternate evidence. I have not seen Per's discussion.

  My two cents. Do NOT take it personally...

Greg Paul (GSP1954@aol.com) wrote, as cited above:

<Estimates of leg extensor mass by H&G limit Tyrannosaurus to a slow pace
whose metabolic expense was ?considerable, but numerous problems cast
doubt on their analysis. The zones in their Fig. 3 imply that running
potential decreases as leg extensors become a larger percentage of body
mass when the opposite is true (the correct question is what is the
maximum portion of total mass that can be dedicated to leg extensors), and
the ?uncertain running ability? zone starts at just 10% when the total leg
extensor/total mass ratio in chickens and ostriches is far higher (H&G,
Alexander 79) (Fig. 1). From only one small modern biped they extrapolated
to far larger sizes without living intermediates. Their estimate of the
leg extensors needed for a juvenile tyrannosaur to run fast (42%) places
it high in their zone of uncertain running ability, and is over twice that
actually present in similar sized ostriches (<20%, less than a third of an
ostrich consists of leg muscles). It is all the more peculiar that their
method predicts increasing extensor mass as limb flexion increases, yet
restored knee flexion is less in the dinosaur than observed in the bird.
The failure to correctly model even a small tyrannosaur falsifies their
results, and their extreme projections for a running Tyrannosaurus must be
considered at least as excessive.>

  Cheers,


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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