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Re: rearing up (long)
"Jaime A. Headden" wrote:
> A problem I see in the rearing sauropod is, in fact,
> it would decrease the blood-pressure given the
> straiter upright neck as the animal went up. The heart
> would move higher, but so does the neck, and
> exponentially so, towards the head, as distance from
> the center of the earth increases.
Exponentially so? Well, I suppose you could come up with an exponent
that might describe it, but I hardly think it is what you are alluding
to. It doesn't matter what distance they are from the center of the
earth. It is easier to pump blood up the farther you are from the center
of the earth, but this makes no difference for these guys as the height
difference is miniscule for gravity effects.
I have never really understood the blood pressure problem people have
with sauropods. Brachiosaurs are clearly designed for an upright neck
posture. Therefore they solved the blood pressure problem. That means
there is no reason why other sauropods couldn't.
Did they rear up? Of course they did. Did they do it as a regular basis?
Well.... Brachiosaurs obviously didn't. 70% of their weight on their
forelegs rules out common rearing for these critters. Diplodocids? Their
morphology certainly looks like it should have been pretty easy for
them. Even with their neck, their center of gravity is over their hips
(for the ones I've seen estimated) making a rearing posture simple for
them. If they did rear up commonly to eat, then having a neck braced to
keep it up would make sense. It would make it easier to support that
way. After all, what is easier to balance, a pole or a floppy hose?
Having the neck braced in the direction they are unconcerned about (that
being backwards) means they have to spend far less energy keeping their
neck held up while rearing. For those of you who might have gotten lost
with my argument, this would look for all intents and purposes as a
sauropod who couldn't raise its neck very well. Naturally, they wouldn't
want the neck to be completely braced because it would like to be able
to reach the tree without moving its entire body. Thus the forward
flexibility as already mentioned on the list.
There is also one other little point I would like to ponder. Sauropods
lasted a good while. It is entirely possible that what may have started
out as a high feeding adaptation was changed to low feeding for some of
them as conditions varied and different species evolved toward different
areas. Might some of the confusion in sauropods be not enough study of
the differences between them? How well understood is the environment
inhabited by all the species? Is there much difference? Just a thought,
I have no information on this and would like some.
Anyway, kaching. This discussion is now $.02 richer.