Re: Sauropod Energetics (Peristaltic pump)

["Kent A. Stevens" <kent@cs.uoregon.edu>]

Sauropod discussion frequently uses the elephant as an analog for  
rearing, and the giraffe as an analog for the neck.  But the sauropod  
bipedality story will be far more difficult to resolve than the  
sauropod neck story (which "only" involves osteology and a  
reasonable, non-naive estimation of cartilage, at least to  
reconstruct an undeflected neck).

Now we'll need to quantitatively estimate muscle moments, the center  
of mass for the portion of the skeleton that is engaged in pivoting  
about the acetabular axis, the starting and ending poses, and more.

But since it seems so hard to get simple skeletal reconstructions  
straight (sorry) for sauropods, it looks fun-but-nearly-hopeless to  
make headway on their rearing up.

Would anyone want to help lay out some ground rules on what would be  
a convincing (if not overwhelming) argument either for choosing  
between the two (mutually exclusive) alternatives:

1) that (at least SOME) adult sauropods engaged in feeding bipedally  
(or tripodally)

or alternatively:

2) NO adult sauropods engaged in bipedal (or tripodal) feeding.

My question is not which is your answer (1 versus 2) but what would  
be a convincing argument for nailing either alternative.

To be constructive, let's please separate the problem into  
biomechanics (which is testable for a range of bracketed estimates)  
and the neural command-and-control coordination issue (which I  
suspect will be far more difficult to resolve).

[Regarding the vestibular coordination issue, ever walk while  
carrying an extended extension ladder vertically, like when you are  
painting a house, and you want to move the ladder around the corner?   
As the upper end of the ladder sways about its up to you to correct  
it before its too late.  In this case you're on the ground looking  
up, and you've got a big clever head on your shoulders.  In the  
sauropod's case, its itty bitty head is way up there, trying to reach  
something to eat while suspended at the end of a dynamically flexing  
neck that's extended above a swaying trunk supported by perhaps  
somewhat wobbly legs on uneven ground, and it's got to decide in real  
time whether the current degree of swaying that feels and sees is  
within tolerance, or whether its time to take a sidestep, or ...]

and

[Oh, and rearing up for mating is just not the same problem (as we  
all know).  Sauropods could rear up to mate as if partaking in a bit  
of mountain climbing, engaging the pollex claw as a crampon, and  
anyway the entire weight of the male need not be maintained in static  
equilibrium during the mounting.  For a sauropod (or an elephant for  
that matter) to sustain a bipedal posture for even a few seconds is  
significantly more demanding, and all for a lot less gain, seemingly.]