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Re: What is biomechanics? (or, The Truth About Flying Snakes - Was: Re: science



Colin McHenry writes:

"Putting 'functional morphology' in the title of a paper doesn't necessarily
mean that you are necessarily performing a biomechanical analysis."

Yes, but don't write off the value of functional morphology. Comparing the shapes of various bones and their articular surfaces may not seem like much, but any definition of the Dinosauria (cladist or not) is rooted in an understanding of form and function. Furthermore, one can establish maxima and minima of movements at particular joints without doing biomechanics (= using models rooted in engineering principles).

"Comparative anatomy  and 'the Extant Phylogenetic Bracket' are but (small)
components of what a biomechanical analysis should include."

Seems to me there would be no way to constrain your biomechanical model without knowing something about the relationships of the organisms. It would seem they are actually critical components of any biomechanical analysis. Do the mechanical properties of bone and cartilage differ among archosaurs? Is a bird a better model than a 'gator? Etc. Comparative anatomy and functional morphology are not some draconian, out-dated tools for understanding dinosaurs. Both of these disciplines have come a long way from the early days of the 20th century, and again are critical both to understanding form/function and phylogeny.

"There seems to
be an tendanncy to use 'comparative anatomy' in the reductionist sense, where comparative
anatomy is the comparison of part with part."


Comparing part with part is essential for you to then understand the whole animal. A comparative anatomist or functional morphologist does not compare parts of the whole because they are being reductionist -- this is the only way to gain a better appreciation of the functioning animal as a whole. If you want to know how a limb really works, you can't just compare its basic shape without considering how the bones articulate, what those surfaces look like, etc. Doesn't one break down a biomechanical problem into pieces as well, and then reconstructs the whole later? This is how all the sciences work -- you tackle a bigger problem by breaking it into managable pieces. Why should this be any different with comparative anatomy?

"As for phylogenetic brackets...well, I'll concede that they can be useful,
but they've been horribly overemphasised of late. The construction of a
biomechanical model should not require any phylogenetic information about
the animal under study - it should be a model of the animal's form, not its
evolutionary history.  The only time were phylogenetics creeps into the
construction of the model is were the anatomy is incompletely known and
anatomical information from related _and_ similar taxa is used to fill in
the blanks."

And won't this occur every time we wish to construct a biomechanical model of a dinosaur? So, isn't functional morphology, phylogenetics, and the comparative method an integral part of any biomechanical study, and not just a peripheral way to get started? In other words, it may not matter whether Tyrannosaurus is a maniraptoran or coelurosaurid, for example in a particular biomechanical model, but its relationships with living relatives are pretty significant for inferring muscles, cartilage properties, bone densities, etc. Furthermore, what if you end up with a novel feature that falls outside the predicted EPB? Well, if you know something about the evolutionary history of T. rex, perhaps you could derive a functional scenario for how the modified structure would work or arose based on phylogenies. This, in turn, would allow you to constrain possible muscle configurations, etc.

I'm all for biomechanical models, and I'm envious of people who have the opportunity to do the really complicated ones (i.e. John Hutchinson), but whether it's phylogeny or biomechanics, the bones and their shapes are all we have for certain. Almost all of our knowledge about dinosaurs springs from the morphology of their fossilized remains, and where all inference and speculation end, bones begin. =)

Functionally yours,

Matt


Matthew F. Bonnan, Ph.D. Department of Biological Sciences Western Illinois University Macomb, IL 61455 (309) 298-2155 mbonnan@hotmail.com MF-Bonnan@wiu.edu http://www.wiu.edu/users/mfb100/

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