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RE: "running" elephants - locomotary analoges




Date: Mon, 7 Apr 2003 22:36:37 EDT
From: GSP1954@aol.com

Hutchinson made an interesting comment that reveals a flaw with his
methodology. It is the digital versus the real world problem.

"I'm not a big fan of using particular extant animals as "models", analogs,
or what have you for dinosaurs.  I prefer understanding the principles and
mechanisms that make living animals work, and using multiple lines of
evidence to see how those principles might apply to extinct animals.  I don't
find analogs/models as very testable (even indirectly) or insightful.  They
mostly head toward dead ends, not in new or fertile research directions."

H appears to be pretty much abandoning what is far and away the best real
world method for investigating animal locomotion, comparative anatomy and
function. in favor of speculative digital simulations. Rather shocking
actually.

Sorry, but this is a blatant mischaracterization of what I think.

For example, this sentence is ignored:
"I prefer understanding the principles and mechanisms that make living animals work, and using multiple lines of evidence to see how those principles might apply to extinct animals." Where is "digital" in this sentence and how is this not "real world"? Where did I say comp anat and function are abandoned? I merely avoid use of analogies, but I still use homologies and other approaches.


It might be a good idea to ask me what I think rather than assume for rhetorical purposes. I love comp anat etc. and have published several papers on it, right? This in itself falsifies this statement about "my digital methodology" without even having to ask. As for how then I come to different conclusions about tyrannosaur running, etc., it is in how the anatomy is interpreted, which will be dealt with in forthcoming papers. Trackways, anatomy, scaling, computer modeling, etc. are all important to me-- this is what I consider to be an integrative approach, combining multiple lines of evidence, as is said above.

I do feel, however, that biomechanics is ultimately the best way to test most functional hypotheses, but not all, and not always using a computer model. When combined with the aforementioned lines of evidence, many of which can be included in a biomechanical model anyway, biomechanics shows how animals work in a quantitative fashion. The power scaling Greg talks about in his post is derived from decades of experiments with real animals and, gasp, even the use of computers to analyze the data! Not from saying "chickens are like humans in some ways so their power requirements must be similar", which would be an analogy-based approach. When analogies with extant animals are used, in my opinion they head down dead-ends. Once someone concludes an ornithomimid worked like an ostrich then there is often little else they can say, and too often the differences are swept under the table in favor of similarity.

And so on, I have many more misgivings with the method that will be explained in later papers. Perhaps this seems like a straw man, indeed there are many shades of gray in what an analogy is and what it tells you, but I do see the approach used in an erroneous way frequently. I am not saying that anyone uses only this approach, but it is used as a primary tool in some research rather than deeper mechanistic approaches such as biomechanics.

As for "digital vs. real world," one need look no further than my work to see that this dichotomy is false. Unlike most other paleontologists who talk about animal function, I have worked firsthand in experiments with living birds, crocodiles, and elephants, with more experiments to come. Hence the sentence "I prefer understanding the principles and mechanisms that make living animals work". Where is this hands-on understanding in the published research of others? Citations of Hatari and nature documentaries replace direct observation and experimentation in many accounts. How is that real world? A VCR and television were used, does that make that approach "digital"? (OK, analog...) Many such people I have talked to also do not even do dissections of living animals, instead relying solely on pictures. Dissection was the core of my research work and is fundamental to any biomechanics I do, with or without computers.

I rest my case; my work speaks for itself. I have not only published digital studies and never will rely only on that. As for my dislike of analogies without a deeper understanding of mechanisms, one can argue with that. I argue that the link between form and function is complex and hence function is often hard to predict from form. Biomechanics allows one to quantify that linkage and tease it apart, within bounds of confidence. Analogy seldom does; it is a qualitative approach (x works like y because form in x is similar to y).

Hutchinson's claim that his methodology is more testable than anatomical
comparisons is spurious, since there is no way to observe if they are
correctly reconstructing the actual performance of fossil organisms that have
no directly comparable living examples.

I would argue that it is a better test because it gets at underlying mechanisms, how animals work, in order to explain how an extinct animal worked. An analogy with a rhino or elephant does not, at least very well. That a computer is sometimes used is irrelevant. The mechanisms are complex and hence sometimes it is impossible or inefficient to understand a mechanism in depth without a computer to help. I'm no math genius; computers are a crutch to make research go faster or even make it possible.


In fact, the actual power output of
leg muscles needed to run at a given speed in an animal of given size
directly tests Hutchinson's methodology for estimating the same, and
convincingly falsifies it.

It does not if one realizes that hands-on experimental work has also shown that power output of leg muscles is often not the primary determinant of running speed. This is in the literature. Sorry, but again people used a computer rather than intuition or paper to do their simple math, so maybe this real world approach is distasteful to Greg.


Hutchinson also suggests that the bouncing gait of elephants "costs more
energy per step because of the more flexed limbs." Again this is digital s
imulation being stated as though it were reality.

I did not use any digital simulations.... This follows the same logic and methods as the standard literature in physiology and biomechanics, some of which Greg implicitly cites in his post.


The real world cost of
locomotion in elephants plots a little below the standard line so if anything
they are energy efficent.

Slow walking is very different from running. Again, explained in the literature.


The supposed extra cost of walking with flexed legs
is based on experiments in which humans move with abnormal gaits, and
abnormal gaits are always energy inefficient compared to the norm. If
ostrichs could be compelled to walk with their leg joints held straight they
would probably be less energy efficient than with their normally flexed legs.
Although it is again counterintuitive, it has never been demonstrated that
leg posture has a significant and consistent influence on power requirments,
since many flexed legged animals are more energy efficient than straight
kneed humans and elephants.

I won't spend energy explaining why this is patently false; it's in the literature and we've rehashed this before.


...there are questions we will probably never
be able to answer no matter what methodlogy is employed. For example whether
some or all were sprinters of distance runners is strongly dependent upon
muscle fiber composition (lots of white fiber means short range, lots of red
long range), which as far as I know is not preserved directly or indirectly
in the fossil record.

Of course, this goes without saying. The "you need a time machine to test your hypothesis" applies to anything done in historical science, and is not a deeply intellectual criticism. We all know it but also know that various indirect methods are useful as tests.




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