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RE: Bipedal apatosaurs and stegosaurs?



Rob Meyerson wrote:

> Assume for a moment that the CG of the diplodicids is located somewhere
>  within the animals midsection (we can argue the exact placement, but I
>  don't think it will be placed in a region so wierd that my point is
>  invalidated).  In order to get into a rearing posture, it would have to 
>  exert a tremendous force to get it's CG located directly over the hips,
>  where it will be more stable.  This posture would place the CG so high,
>  that it would have to constantly correct itself to keep from falling over. 
>  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)

Actually, the extremely long tail of Diplodocoids probably placed the CG
somewhere almost directly in front of the pubes, not way up under its heart.
When the animal reared, the CG would not be much higher than where it was
while the animal was on all fours.  You also seem to forget that all bipedal
animals are constantly correcting their posture so that they don't fall over.
I doubt that standing is a real calorie burner, but who knows.  Also, I think
that tripodal feeding would be more space efficient in a semi-dense forest.
What if a hypothetical Diplodocus ate all the foliage directly in front of its
face while feeding on all fours and wants to go to a tree over there on the
left, but darnit, there's a small tree in the way of his neck.  So now
Mr. Diplodocus has to walk all the way around the tree to eat the foliage down
low.  What I am saying is that Diplodocoids were probably too long and
straight to have survived in a semi-dense forest, so tripodal feeding and
perhaps bipedal walking, were the only ways they could manoeuver around in the
forest.

>  As I have said in previous postings, for the smaller diplodicids, this may
>  have been a valid strategy.  For the really big ones, the amount of foliage
>  reached by rearing would be so small as to make the posture uneconomical (a
>  90' diplodicus reared up would have it's head at the very tops of the
>  pines, and there isn't that much foliage available for consumption).
 
Actually, a 90' Diplodocus would not have it's head at the very tops of the
trees, unless of course you're advocating that they bounced on the tips of
their tails Tigger-style...  It's head would maybe be about 30'-40' high, not
the 70'-200' heights that mature evergreen trees reach (and I assume did
reach).

> Any theropod that attacked from the front could find itself a nasty smidge
>  on the ground.  However, if Allo came in from the rear and zeroed in on a
>  thigh, it would be able to get in close with relative safety.  This style
>  of attack would also keep the predator clear of the tail as it comes
>  off the ground.

Well... that's very lucky for the Allosaur IF it got in close enough to the 
Diplodocoid without being seen or heard.  This is random speculation, but I 
would think that perhaps they had fairly well developed ears.  Anyways, why 
also, do you assume that Diplodocoids were sloth-slow?  Just because they 
couldn't walk very fast, doesn't mean they couldn't MOVE very fast.

Peter Buchholz
gpb6845@msu.oscs.montana.edu

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