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Tyrannosaurus paper

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.


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