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RE: Bipedal apatosaurs and stegosaurs?

Nick Longrich writes;

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

Actually, I don't see the tail being all that massive; certainly not massive
 enough to radically change the CG position.  Besides, the tail verts are
 rather hollow as well, which would reduce the *tails* weight.

>As has been pointed out, diplodocid necks at best stick straight
>out, the Dicraeosaurus illustration I looked at actually had it pointed
>*down* slightly.

The necks may  *start* with a downward direction, but that doesn't mean that
 they had to stay that way.  The neck of Diplo seems rather flexible, and
 would've been able to reach above body level.  As I mentioned to someone
 off-list, the diplodicids may have gotten longer for the same reason that
 camarasaurids got bigger, they both get a better reach far more efficiently
 then they would by rearing.

>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.

Nature is not this simple.  Consider diplos not as giraffe-style feeders,
 but as elephant-style feeders (where the diplo neck and head are analogous
 to the  elephant trunk).  This may be more appropriate.

>These 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

All these anatomical features could also be explained as convergence.  Since
 both groups used their tails as anti-predator devices, we would expect both
 groups to be  well developed in the hindquarters.

Besides, a rearing stegosaur would be suicide, since the tail spikes would
 be effectively out of action while the animal was feeding.

Rob Meyerson
Orphan Vertebrate Paleontologist

"If anything is going to go wrong, it'll happen at maximum velocity."
                        -Red Green