Brachiosaur Forelimb Proportions (Was: Isle of Wight)

[Mike Taylor <mike@tecc.co.uk>]

Guys,

A few days back, I wrote:

> Date: Tue, 24 Jul 2001 10:21:51 +0100
> From: Mike Taylor <mike@tecc.co.uk>
> 
> through restoring.  The most obviously impressive [Isle of Wight
> brachiosaur] material is a cast of a complete (except for the toes)
> forelimb, which they have completely prepped and taken away.  The
> forelimb stands seemingly unsupported in the middle of the room.
> It's very odd.  But more about that in a separate message.

OK, time to explain.  The oddness is in the cross-section of the
humerus.  Stupidly, I didn't take any photos, even though I had my
camera with me; and I don't have accurate measurements; but folks,
that bone is weird.  It's more like a blade than a tube.  My rough
estimate would be that it's something like six inches wide
medio-laterally, but no more than an inch and half think
cranio-caudally.

So two questions.  Firstly, isn't that just wrong for a brachiosaurid
humerus?  I'm pretty sure I saw a B. humerus in the Smithsonian last
year, and that sucker was extremely thick, and more or less round in
cross-section.  Diagrams that I've seen lead me to expect that shape
too.

And secondly, surely such a medio-laterally wide blade shape just
makes no biomechanical sense?  You'd think that if the humerus was
going to be significantly bigger in one dimension than another, then
it would be cranio-caudally, so that it could better absorb the forces
of acceleration and deceleration when starting and stopping walking.

So what's going on here?  I'm sure that much better informed DMLers
than I have seen this exhibit, and can tell me what bonehead mistake
I'm making.

Thanks,

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor - <mike@miketaylor.org.uk> - www.miketaylor.org.uk
)_v__/\  Tom Holtz's rule of dinosaur restorations: if you can't fit
         the skeleton inside the model, the model is wrong