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Re: ilia and masses



----- Forwarded message from dexter dexter <dexter1647@caramail.com> ---
--
From: dexter dexter <dexter1647@caramail.com>
To: jrhutch@Stanford.EDU
Subject: Re[1] DINOSAUR digest 2041
Date: Tue, 05 Mar 2002 06:27:35 GMT+1

Titanosaurs have very large iliums, true, but not in
relative to their sizes. It is very possible that large
theropods (As stated early, % of body mass in leg muscles
grows with size, and ostriches still have ~20%. In order to
move 5 m/s (like in the study), T-Rex would need ~29% of
it's mass in leg muscles, which is very high, but not
impossible.
========

This is a perceptive comment that I was sure someone would notice, and 
it is important.  In the longer paper, I will explain this much 
better.  Limb orientation (joint angles) mean a lot; the muscle moment 
arms can actually increase in a more straight-legged pose (we didn't 
show this in the current model, but it is correct), and the GRF moment 
arms decrease.  So a subtle point of the paper is that a walking 
tyrannosaur would be MUCH better off than 29%, perhaps even down to 5%, 
if it has straighter legs.  It would be a misinterpretation of our data 
to say that our model shows that Tyrannosaurus could not walk or stand; 
the model shows plenty of strategies that are consistent with known 
data and would work.  Again, I'll explain this more in the next paper.

We do not know exactly how tyrannosaurs stood.  A lot of arguments have 
been made in detail based on joint anatomy, but I don't buy them.  They 
make a lot of assumptions about what is articulating where and assume 
that there is no joint cartilage that would change things.  From my 
manipulations of 3D bone models, I can't conclusively rule out most 
poses that authors have reconstructed Tyrannosaurus in.  This is an 
important issue that others have glossed over.


========
Yes, but there is nothing alive today that resembles to a
bird which can even hope to come close to 6,000 kg ...
========

Show that I must be wrong, then.  You've shown nothing to the contrary.

==========
Actually, from what Thomas Holtz told me, Anderson's method
"underestimates" weight. You will notist in Currie's 2000
_A.atokensis_ paper, he mentions that the Anderson weight
estimate for MOR 555 is 4,160 kg. Vollumetric estimates will
go as high as 6,000 kg, I think.

==========
Yes, I meant underestimates; my bad.  Volumetric estimates such as 
Henderson's 1999 model go up to ~7800 kg or so.  See Seebacher 2001's 
review.