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Re: (sigh)sauropod necks again--long! -Reply

"Augustus  Toby  White" <toby.white@chamberlainlaw.com> claimed:

> Although it would not take much oxygen to fully supply the brain, a
> sauropod brain is presumably made of pretty much the same stuff as a
> giraffe's.

In case the rearing of the head of the rearing of the sauropods thread
wasn't bad enough, I'm going to risk starting off another ugly
exchange by mentioning that the above isn't necessarily true if you
add in nuances about thermoregulatory physiology.  As others have
noted time and again, mammalian neurons are generally more energy
intensive than reptilian neurons because their membranes are leakier
to electrolytes.  Mammalian neurons need relatively large amounts of
oxygen to maintain the appropriate intracellular and extracellular
concentrations of sodium, potassium and chloride.

In other words:

> There's no reason to think that the sauropod brain could withstand
> oxygen deprivation any longer or better than a giraffe,

is wrong -- I've just given a potential reason.  It might also be
instructive to analyze how hypoxia effects the brains of different
animals.  During the last ten years it's become increasingly clear
that the primary mechanism of brain damage (in the short term) for
humans experiencing a stroke is excitotoxicity.  That is, if a region
of the brain is deprived of oxygen, many of the neurons in that area
suddenly become excessively active, and then they die.  Although I
don't recall what all of them are off the top of my head, many of the
steps in this physiological reaction are fairly well understood.
Physiological adaptations could make this reaction less likely if an
animal's normal behavior might lead to significant periods of cerebral
anoxia.  I think most work on this area has been performed on
mammalian brains since preventing damage to humans suffering from
strokes is the main reason people have looked into this topic.  But I
suspect that others have also looked into the manner in which hypoxia
affects the brains of other animals more closely related to dinosaurs.
Can anyone else shed any light on such research?

Mickey Rowe     (mrowe@indiana.edu)