RE: "running" elephants - locomotary analoges

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

> 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
===========================================