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RE: How much does a dino weigh?



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> philidor11
>
> You wrote:
> <So, errors of 25% might not be unexpected for mass calculations on good
> specimens, and much greater for incomplete forms.>
> and subsequently:
> <Yeah: the models some people used were crap.  Tom's Rule Number One in
> dinosaur restorations: if you can't fit the skeleton inside the model, the
> model is wrong.>
>
> Even at 25% error, presumably associated with a good model and complete
> specimens, a substantial overlap would mean that a 95%
> probability that one
> animal weighed more than another might be hard to achieve.
> When you hear discussions of the biggest predator, or for that matter the
> biggest cheese wheel, do you assume they're talking about length
> (circumference of a cheese wheel), weight, or some combination?

First off, when I hear discussions about the biggest predator, I think "oh
gads, here we go again"...  :-)  In any case, for organisms the most
important size attribute (in terms of biology) is mass: that is, how much
critter is there?  Most aspects of physiology (respiration, circulation,
food intake, etc.) are associated with mass more so than length.  On the
other hand, linear dimensions are, of course, easier to retrieve from the
fossil record.

> <Of course, the real test for this would be taking a number of
> skeletons of
> different modern taxa from individuals whose life mass was known, then
> estimating the mass from the skeleton, then comparing these
> estimates to the
> known mass.
> As you might imagine, this would be a sizable and time-consuming effort.
> Nevertheless, it would give some statistical idea as to the expected
> accuracy of mass calcuations based on fossil bones.>
>
> How do you know that the model is good?

To start out with, apply Tom's Rule Number One (see above).  Unfortunately,
many of the models used in past studies (and particularly throught the
pre-1980s) were more artists' impressions of the animal rather than a
rigorous attempt to sculpt the animal from the bones up.  Hence you wind up
with models (such as some that Colbert used in his study) where the shape of
the skeleton of the organism simply won't fit inside the reconstructed
model.  To use an extreme example, I would not have much confidence in using
the Waterhouse Hawkins reconstructions of _Iguanodon_ and _Megalosaurus_ for
determining how massive either of these taxa were!  However, the models
Colbert used, while better, were still done in the manner that would be
required today (that is, start with a scale model of the actual skeleton,
and flesh it out).

> If, as you imply, the model(s) in
> use was not developed from modern animal skeletons and known solutions,
> where does it come from and how was it validated?  Is there more than one
> model?  If so, have they been compared for similarity of results

I think you misunderstood my previous discussions, and have conflated some
different arguments.  To break it up into different parts:
I) Many of the models used in past studies were artist impressions rather
than accurately measured reconstructions of a particular specimen.  These
were done in reference to modern animals in one sense (the classic use of
knowing where to put the muscles).  Also, for some dinosaurs there are of
course many different models available.

II) In reference to modern animals: this goes back to the question of
accuracy of even an excellent model.  In order to say something statistical
about accuracy, we'd need to have some form of reference.  I suggested a
potential study (which would be terribly expensive and time consuming, mind
you) that would at least allow for the beginnings of a statistical basis for
determining accuracy of flesh reconstructions.

> Quick Watson, the game's afoot!  (Of course, when Holmes said
> that he was on
> his way to going over the Reichenbach Falls, but then again I'm no Holmes
> and you're not Moriarty.)

I'm not?  I guess I'll have to turn in my Master Criminal card then... :-)

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796