Re: standing t-rexs

["Matthew Bonnan" <mbonnan@hotmail.com>]

Cliff Green said:

    "I have a question  that has to do with my dino art. Could a theropod
like T-Rex prop itself up on its haunches like a kangaroo, just like in the
old Charles R. Knight renderings? In my own meager anatomical studies, I
haven't seen a problem with this being able to happen. Any input would be
most appreciated."

I'm no theropod expert, but one of the reasons why T. rex cannot rear up 
into the position you suggest is that the femur would have to become 
disarticulated to do so.  As far as I know, the acetabulum (hip socket) of 
T. rex, like other theropods, has a bump called an antitrochanter.  There is 
also a notch (again, as far as I know) on the back of its femur, near the 
femoral head.  The femur can only extend so far past vertical before the 
notch on the back of its head locks with the antitrochanter.  This appears 
to prevent the femur from rotating far enough back that the upright position 
of many museum specimens would be rendered impossible.

In the 1980 book "A Cold Look at the Warm-Blooded Dinosaurs," the late Nick 
Hotton describes very well the fundamental difference between the mechanics 
of a mammalian femur and acetabulum and that of a theropod dinosaur.  I 
suggest you read his chapter for more information.

And, yes, as G. Paul has explained in his PDW book, the hip and pelvic 
musculature may have also prevented theropods from assuming such a "regal" 
position because assuming it would also mean avulsing most of the hip and 
pelvic muscles!

Good question.  Any thoughts, oh theropod mechanically inclined ones?

Matt Bonnan



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