Tyrannosaurus paper

[John R Hutchinson <jrhutch@stanford.edu>]

Hi folks,

        

A few very
brief notes about the paper, FYI.  There is a much lengthier
discussion of it in progress on the dinosaur listserver, as you might
expect, and it's been fun.  I won't clog your e-mail with it. 
The webpage at the bottom of this e-mail is a site we set up in order to
clarify what we actually said in the paper.  All reporters got a
chance to read it in order to prevent misinformation.  I recommend
to future Nature/Science authors to try something like this; it was fun
and prevented a lot of errors.  In general, I think reporters have
done a fine job of covering this.

        

Although
our analysis, like any science, might be falsified by later work, or
upheld, our hope is that it stimulates more biomechanical work in
paleontology.  I see a wonderful trend recently in doing more
rigorous biomechanics in our field, and I hope it continues.  One of
my reasons for writing the paper was that I felt like we've been using
the same methods and evidence for the last 25 years, especially the
then-innovative work of my hero, R. McNeill Alexander.  Our paper is
a simple example of how we can bring newer methods from biomechanics into
paleontology and test some challenging biomechanical hypotheses.  In
other words, we need to "raise the bar" for paleobiology. 
We have the tools and the data from living animals in order to do it now,
and it's great that many people are using them.

        

An
important point of the study is that sensitivity analysis, or varying the
unknown parameters in the model to see which ones matter, is an important
tool for studying the biomechanics of extinct animals, and other
biological problems.  That is nothing new to many people, but I
wanted to explicitly emphasize it.  When reviewing a submitted paper
for a scientific journal, I think it is important for reviewers to keep
this idea in mind.  What parameters are known vs. unknown? 
Which ones are really important, and how much reasonable variation might
there be in their values?  We did a fairly simple sensitivity
analysis in the paper as an example, and are doing more complicated ones
now.

        

Second,
are all of the data that are needed in order to evaluate the model
present in the paper, or at least are the relevant references
cited?  I've read quite a few peer-reviewed
"paleobiomechanics" papers lately that do not present enough
data in order to replicate or even understand how the authors got their
results.  I think we put enough data in the Nature paper for anyone
to test our work.  Do note that the Supplementary Information
contains a lot of extra data, and Table 1 has a printing error that is
noted on our website and will be corrected in a Nature erratum.

        

A third
important point is that any model of extinct animals should be shown to
work for at least one, and preferrably many living animals.  As much
evidence from neontological data should be used as possible in order to
constrain speculation.  We modeled a few living animals to test the
model, and have done more since then that continue to support its general
validity.  Like any model, our model is just a hypothesis and needs
to be tested and refined continuously.  This ties into the point
above, that the models of Alexander et al. were an important
"paradigm shift" but we can do much better now, and many of
those assumptions need to be re-evaluated.  For example, researchers
in biomechanics are beginning to show that the Froude number is not
always an adequate descriptor of dynamic similarity; see work by Max
Donelan, Rodger Kram, Jerry Pratt, and others.

        

Finally, I
want to strongly make the point that anatomy alone is not necessary and
sufficient to understand locomotor biomechanics.  This is so
important, I really want to emphasize it.  We need to move on using
techniques from trackway studies, biomechanics, morphometrics, and other
lines of evidence.  Our paper uses some simple physics because in
order to move at any speed, an animal must be able to exert a certain
amount of force.

        

Whether
our study is right or wrong, if it convinces anyone to use more
biomechanics in their research, or inspires students to learn more
scientific techniques, we will be very happy.  Thanks for your
time.

Sincerely,
John

        

        

===========================================
John R Hutchinson
NSF Postdoctoral Research Fellow
Biomechanical Engineering Division
Stanford University
Durand 209, BME
Stanford, CA 94305-4038
(650) 736-0804 lab
(415) 871-6437 cell
(650) 725-1587 fax
http://tam.cornell.edu/students/garcia/.trex_www/naturepaper.html
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