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rearing up (long)



Although I have been on this list for a number of months, this is my
first post -- though I have been tempted on a number of other occasions.

"k. clay" wrote:
> 
> List:
> Please allow me to try my hand at answering some of these interesting
> topics with my usual disclaimer that my vertebrate knowledge is almost
> entirely confined to humans.

My own vertebrate knowledge is, well...... not as great as I wish it
were but..........  I'd still like to offer a couple of cents worth.

<snip, snip>

> 3.  In terms of the sauropod rearing question, with their small brains
> and presumably small-diametered cerebral arteries I have been under the
> impression they would not require that much of an increase in blood
> pressure to perfuse their brains.  I believe I heard somewhere that
> turtles can function for quite some time with their cerebral circulation
> entirely disrupted (was it a Bob Bakker quote?).  Would not a rearing
> sauropod be able to increase her cerebral blood flow by increasing the
> heart rate slightly, asking the adrenals to kick out a little more
> cortisol and adrenaline, and increase the sympathetic nervous system's
> firing to the peripheral arteries and veins thereby shunting blood to
> where it's needed most, without raising intracranial pressures to
> dangerous levels?  I believe so.

Ken, I agree with you completely.  Increasing cerebral blood flow for a
sauropod (or any other animal, for that matter) should not be a problem,
for exactly the reasons you have listed.  The real problem would be
decreasing cranial pressure when lowering the head -- such as to drink
or to eat the scrubs.  May I suggest that the animal to look at for an
understanding of control of cranial pressure would be the giraffe?  This
animal would literally blow its brains out when it drinks if it did not
have a vascular rete to equalize the pressure.

Roberta Meehan, PhD (but not in dinosaur-ology)