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RE: Bipedal apatosaurs and stegosaurs?

Stan Friesen writes;

>> Even among the diplodicids, I have a hard time seeing a herd of the
>> big ones all rearing up to feed on the tops of the pines.  The loss
>> of efficiency aside,
>I am unsure of how great the loss of efficiency would be.

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)

>I think if they ingested large quantyities of foliage each time they
>reared up the loss would be *relatively* small.

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).

>>Even if the Diplo saw the theropod coming, it would take a lot of
>> precious time for the animal to = get all feet on the ground and to
>> engage it's tail for combat.
>Why bother - just bring the front feet down on top of the nasty little
>allosaur! Really, given the large size disparity, the front feet of
>a rearing diplodocid would be higher than the back of any known allosaur.

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.

>In fact, this may well have been a more effective defense mode for
>a thin-tailed Diplodocus than using its tail anyway.

I don't know, a well placed whip could be a very effective deterrent/defence.

Rob Meyerson
Orphan Vertebrate Paleontologist

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