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Models and criteria



Kris (MariusRomanus@aol.com) writes a nice clear post using meteorological models' seeming inadequacies to suggest that general models are unreliable, and models should be specifically tailored for each case, such as each organism. He also suggests that my criteria for proving my work wrong are unrealistic or unfair.

In the case of the animal locomotion models that have been used for decades and repeatedly validated, I disagree that a general model is not reliable enough. I know what all the parameters I am putting into the model mean, and which ones are least certain, and I know which ones I've left out, and what they might mean if I did add them in. So in general, I trust the applicability of my models, but I'm never one to stop with a model and assume my work is done. That's why I wrote a newer paper that goes into more detail, and that's why I'll continue to do so. Also, I am indeed designing animal-specific models: 3D models of every individual muscle group (rather than harmonic means of muscles acting about joints) in a variety of animals. That we do not have tyrannosaurs to dissect does not make modeling them a fanciful or meaningless exercise; it just depends what you put into the model and how carefully you examine the uncertainty in the model parameters.

To resolve this controversy, dismissing models or anatomy or any approach as not useful or reliable is not the way to go. I won't talk any more about that; it's beating a dead horse and was covered 6 months ago. Even if the model is wrong, the model can be used/modified to explain why, that's why models are useful.

To be pro-active, I'll outline a few examples (there are more, I am sure) of how I think the entire debate could be resolved:

A. Falsifying our model:
1. Showing that the model method we used actually does not apply to living animals in general. I put this in as a rhetorical case more than as a good option. It would take tons of work to do, and would basically show that some 30 yrs of animal experiments and modeling all are wrong. It would have to show more than just that the numbers are a little off; it would have to show that they are way off, changing the conclusions drastically.
2. Showing that the data we put into the model are inaccurate for Tyrannosaurus (because of scaling assumptions, parameters excluded, etc.), and using the model or a modification of it to show that more/better data give a fundamentally different result. Such an approach would not only need to show that the parameters I put into the model were bad, in my opinion, it would also be best if it showed that the parameters we left out of the model on a conservative basis do not matter. In other words, finding a solution for a very low T value that makes sense (i.e. not using 1cm muscle fiber lengths). This is realistic; it could be done.
3. Similar to above, developing a model that works much better than the one we used, and gives different results that totally contradict ours, yet still being validated for living animals. Very do-able. I may even unwittingly do it with some of my newer models; who knows. I'm not afraid to prove myself wrong.
4. Discovery of an unambiguous 11-20m/s running adult tyrannosaur (or other huge theropod) trackway. Quite conceivable.


B. Supporting Greg et al.'s hypothesis: (Falsifying our model does not prove Greg's right)
1. Developing a biomechanical model that shows tyrannosaurs could run 11-20m/s, and works for a variety of living animals and small dinos. I know they're doing something like this, and I might stumble across the same thing and show that I was wrong.
2. The trackway mentioned above.
3. Showing that the anatomy Greg sees as being indicative of 11-20m/s running really results in that speed. Perrsonally, I think this would require a biomechanical approach similar to #1 above, but there might be another way (e.g. a good non-biomechanical scaling study) that would be convincing that I haven't thought of.


And I think the opposite of each case above (using other models to support what I've done, which I and others have already succeeded in doing, and Don Henderson's work suggests as well, or falsifying Greg's hypothesis with an alternative approach) is also important.

Sure, none of the things I've listed above are easy to do. To me, that is satisfying, because it leaves plenty of work to be done for everyone involved.

To my mind, none of these things above have been done to my satisfaction. Maybe I'm hard to please. Thus I do not consider the controversy settled, which is why I continue to work on the problem and probably will for years. If I thought it was settled, I'd work on something else and wouldn't respond to criticism. Maybe someday I will be convinced that I am wrong, and then I will write papers using living animal experiments, models, anatomy, etc. to help explain why I was wrong, and jump aboard that old bandwagon. But for now, I want to be convinced first.

Obviously one or the other side of the controversy must be wrong eventually. There may be a middle ground that we're both missing, although the way we phrased the paper left a lot of shades of grey that I'd consider middle ground we covered. I don't know if Greg thinks his hypothesis could ever be wrong, and that's what concerns me. It would be interesting to hear him say that much; "Who knows, I could be wrong." But the tone of his and some other folks' posts suggests to me that they see things in a black-and-white fashion: he must be right and I must be wrong, based purely on what evidence is available right now. Whenever I hear (or think I hear; maybe I'm misrepresenting his thoughts) dichotomous thought like that in paleontology, I feel dubious and look for holes in the science.

That's what people are doing now with my work: looking for holes. And that is fine with me; in fact I would be more worried if I did not hear of controversy! Nothing is worse to a researcher than a field with all big questions already solved; that's why I love paleontology. I will still defend my work as long as people don't convince me otherwise. If they find something dramatic that changes the picture, then science has progressed. And we'll move on to something else. Likewise, if my work is supported, science has progressed. It's all about learning through hypothesis testing and reliable methods.

--John R Hutchinson