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RE: Bipedal apatosaurs and stegosaurs?



On Wed, 16 Oct 1996, Robert J Meyerson wrote:

> Assume for a moment that the CG of the diplodicids is located somewhere
>  within the animals midsection 

        The short chests, long, heavy tails, hollow forward vertebrae and
reduced forelimbs of Diplodocids all help move the center of gravity
backwards.

>  All this would use up a lot of energy.  It would be far more efficient to
>  stay on the ground and feed on what is readily available, then move to the
>  next tree (especially in a pine forest)

        The real problem with this is that it is not anatomically
possible. As has been pointed out, diplodocid necks at best stick straight
out, the Dicraeosaurus illustration I looked at actually had it pointed
*down* slightly. Diplodocids would make absurdly bad giraffe-style
browsers because of the downard direction of the neck and short forelegs
that only compound the problem. Either they grazed, or they reared. 
        Think of a diplodocus as a big balance. The hips are the point of
rotation, they must be able to support the entire animal's weight while
rearing, and most of it while perched on the hindlimbs and tail. This
would explain why diplodocids have such huge hips and hindlimbs. The body
must be able to support the forward end of the animal up in the air-
hence, the tall, fused vertebrae over the hips that allow the animal to
suspend the front, suspension-bridge style, from the hips. It must reduce
the weight and leverage of the stuff in front of the hips- this is why
the anterior vertebrae are so heavily hollowed. This is why the chest is
so short, to reduce the leverage it exerts. This is why the forelimbs are
so short, to reduce the amount of weight that must be pulled upwards. This
is why the neck doesn't need to bend upwards to let these animals browse,
and why they don't need long, giraffe-style forelimbs. Most of the same
arguments apply to stegosaurus, despite the puzzlingly short neck of the
animal. Notice that stegosaurs and diplodocids bear a striking degree of
similarity in their overall body plans (same forelimb-hindlimb ratio, same
big tail, same downcurved spines, same big hip spines, same big tail,
etc.) with the exception of the neck.