Re: Quadruped theropods?

[don ohmes <d_ohmes@yahoo.com>]

Is a man doing the breast stroke an aquatic quadraped? { ; ) =B  >==|

Don

----- Original Message ----
From: Graydon <oak@uniserve.com>
To: dinosaur@usc.edu
Sent: Monday, May 22, 2006 1:37:42 PM
Subject: Re: Quadruped theropods?

On Mon, May 22, 2006 at 09:05:10AM -0500, Tim Williams scripsit:
> Graydon wrote:
> >Arboreally, they're suspended from, not supported by, the forelimb;
> >I'm not sure that counts as a quadrupedal stance, since they're not
> >putting a compressive load on the forelimb.
> 
> How do you figure?

Well, a terrestrial quadrupedal stance the mass of the body providing a
force vector down, and the structure and muscles of the limb providing a
resisting force between the body and the supporting surface.  This tends
to lead to things like pads on the feet and arrangement of the skeleton
and connective tissue to take loads via passive support as much as
possible.  Those loads, and the main structural loads, have to pass
through the forelimb where (even in sprawling lizards) the stress is
compressive and more-or-less perpendicular to the axial skeleton.

The arboreal clambering stance has the mass of the animal hanging from
the forelimb; the resisting force is above the body, and the alignment
of the stress is more-or-less parrallel to the axial skeleton.

I'm dubious that these are equivalent locomotor postures.