Re: The heart of a Brachiosaurus

["Joseph C. Daniel" <jdaniel@aristotle.net>]

John Bois wrote:

> I don't know the answer to your question.  But here are some things to
> think about.  Much depends upon whether or not the animal raised its head
> directly above its body, or whether it browsed closer to the ground.  In
> the first case one would expect high blood pressure or some fantastic
> adaptation (eg., 7 neck hearts) to get the blood all the way up.  I
> believe brain tissues (for example) in all creatures are equally prone to
> bursting (as in strokes).  Therefore, if excessive pressure was needed to
> pump blood up then one would expect an excessively high rate of strokes.
> We have no way of knowing whether or not this occurred.  I wonder if
> giraffes experience more of these difficulties?

This isn't really true. High blood pressure at the level of the heart does not
equate to high blod presure at the head. The blood pressure at shoulder level 
for
giraffes runs about 250 mm Hg, at the head it is a mere 120, pretty much equal 
to a
human's. For point of reference, the giraffe does not have the highest blood
pressure of known animals. That honor goes to the common domestic turkey. These
animals have upwards of 400 mm Hg blood pressure and have no specific 
adaptations
for high blood pressure. They do as a result suffer high incidence of aortic
failure. Praise be excessive inbreeding for the perfect Thanksgiving dinner.The
giraffe, by the way, does have adaptations to prevent high blood pressure at the
brain when it lowers its head below its heart, but I would have to do a little
research to remember exactly how it doe this.
As far as the Brachiasaur blood pressure, the last estimates I heard would put 
it
about 600-700 mm Hg. Far above anything today, but I see no reason why it could 
not
have done so. For an animal that big, the carotid arteries are going to be much
stronger than animals of today simply because of the scaling up of the carotid
walls. I have seen no compelling hematologic argument that would stop the
Brachiasaurs or any other sauropod from holding its head high.

> Either way, moving blood around a huge body was just one of the
> physiological problems to be solved by these gigantic creatures.  Indeed,
> one could argue, as I have, that being big was a rather pathological
> condition.

Ain't that da truth.

Joe Daniel