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Re: Sauropod Energetics (Peristaltic pump)
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
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 ...]
[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.]