Re: *Brachiosaurus* labyrinth paper...

[mike@miketaylor.org.uk (Mike Taylor)]

> Date: Fri, 01 Jul 2005 12:56:20 +0200
> From: David Marjanovic <david.marjanovic@gmx.at>
> 
> I'm currently reading the must-read
> 
> Andreas Christian: Neck posture and overall body design in
> sauropods, Mitteilungen des Museums fÃr Naturkunde Berlin,
> Geowissenschaftliche Reihe 5, 271 -- 281 (10 November 2002).
> [...]
> His method is not influenced by systematic errors, so the actual
> weight of the neck doesn't matter, just the relative weights of its
> segments.

However, his method (actually Preuschoft's) depends on what seems like
a very questionable assumption, namely that the habitual posture of an
animal's neck is the one that most nearly equalises the stress exerted
on the intervertebral discs.  I can't for the life of me see why this
should be true.  If a useful posture entails more stress on
intervertebral joint A than on B, the animal is hardly likely for that
reason to favour a posture in which the stress on B is _increased_ to
match that on A.

I had a strong negative reaction to the paper in which Christian first
applied this method to sauropod necks (Christian, Andreas, and
Wolf-Dieter Heinrich.  1998.  The neck posture of _Brachiosaurus
brancai_.  _Mitteilungen aus dem Museum fur Naturkunde, Berlin,
Geowissenschaften, Reihe, 1, p73-80).  To be fair to Christian 2002,
though, it does apply the method to a couple of extant critters and
gets the "right" answer, so at the very least it's a big improvement
over the 1998 version.  By the way, at SVPCA 2004, Christian presented
a talk on the same method applied to _Euhelopus_, for which he again
derived a vertical posture.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
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