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RE: Tyrannosaurus was not a fat boy or girl



We have contributed some data on this for living animals- see Allen et al.
2009 in Anat Record (pdf available below); e.g. the mean body density of
crocs isn't that different from birds-- or saurischians more generally
(according to output ranges from our models). There are still not as much
published data on body (or regional) density as one would like. We're
working on that...

But the best approach for dealing with the uncertainty caused by density is
simply to do sensitivity analysis, as one should do for any quantitative
paleobiological estimates; see how much what you don't know matters, by
varying parameters within a plausible/known (from EPB) range and seeing what
variation in results you get. The benefit of 3D digital models, as has been
noted ad nauseam, is that it's all explicit and can be dealt with in any
level of detail one wants. We build abstract air sac/lung regions generally,
but add more detailed ones where cavities/spaces are clearer (e.g. cranial
sinuses, trachea). And then we vary the sizes of those because we can't be
sure of their precise extent.

Because you then get a wide range of results, any specific estimate of mass,
speed, etc. is almost certainly wrong (and naive), as I and others have
emphasized in our papers. The modern/scientific approach is to estimate the
plausible range of possibility and exclude implausibilities or
impossibilities. So of course one doesn't need a time machine to do science.
One just needs to do some work and be careful.

http://www.rvc.ac.uk/sml/People/JRHPublications.cfm

Cheers,
John

-----Original Message-----
From: Augusto Haro [mailto:augustoharo@gmail.com] 
Sent: 24 October 2011 18:16
To: Dinosaur Mailing List
Subject: Re: Tyrannosaurus was not a fat boy or girl

How is the degree at which pneumaticism reduces the density of the
body assessed in mass estimates? Although you can infer the proportion
of the skeleton which is pneumatic, it looks impossible to tell what
part of the non-skeletal volume is filled with air sacs. However, I
think I once read (probably from Gregory Paul) the claim that body
density is not much lower in birds than in other tetrapods because the
pneumatism is countered by a more solid lung in birds, contrasting
with the larger air cavity of the lung of other vertebrates.