RE: Bipedal apatosaurs and stegosaurs?

[Nick Longrich <longrich@phoenix.Princeton.EDU>]

On Fri, 18 Oct 1996, Robert J Meyerson wrote:
> 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.
        It is bigger than in any other group of sauropods, and the large,
dorsally positioned caudal ribs indicate massive muscle attachment from
the caudofemoralis.

> 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.
        But if it were expressly designed as a giraffe-style feeder, it
would have the neck upcurve and long forelimbs, like Euhelopus and
Brachiosaurus.

        At SVP there were some guys modeling exactly this. Turns out that
Apatosaurus, according to them anyway, does have a bit of play up and
down, which would fit with the facts that it has a shorter neck and is
much more heavily built- i.e. it could probably rear, maybe just not
nearly as well. It may have been more of a generalist, so yes, I am overstating
and being generally full of @#%% when I try to categorize everything as
either-or. I imagine that Apatosaurus did both. Apatosaurus yahnapin,
if memory serves me right, actually did have the upward kink at the base of
the neck, so it may have not needed to do this very often.  Diplodocus,
on the other hand, is much more lightly
built, and reconstructions showed relatively little upward mobility of
the neck, so it probably employed rearing much more often. Another animal
at SVP, Amphicoelias?(not _fragillimus) appears to be sort of between the
two- it is relatively lightweight, quite short- 30-40 ft? and has a short
neck.
        So more and more recently I've been thinking that  probably sauropods
employed a wide range of techniques that varied from family to family and genus
to genus, employing to varying degrees low-feeding, mid feeding,
giraffe-style high feeding and tripod-style high feeding.

> 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.
        Yes, I'll agree with you on that and apologize for trying to
narrowly define animal behavior. While an animal may be specialized for
one particular niche, this does not prevent it from exploiting, even if
somewhat less efficiently, a niche for which it is not optimized. Wolves
hunting rodents, for example, or foxes digging up the sand-lance fish out
of the sand.

> >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
> >neck.
>
> 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.
        There are club-tailed sauropods that do not show such development in
the hindquarters, I believe- some of the chinese ones (not Shunosaurus).

> Besides, a rearing stegosaur would be suicide, since the tail spikes would
>  be effectively out of action while the animal was feeding.
        You could also say that rearing in the gerenuk is suicide- after
all, it can't run away bipedally. But it does it anyway.