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Re: Running around like an Ornitholestes with his head cut off...




On Fri, 16 Sep 2011, Scott Hartman wrote:
Ok, to tie back Richard and Jason's morbid (but informative) posts

Morbid? MORBID? I believe this would be where a Mad Scientist rant
would kick in...

back to the original issue of nervous system evolution and
centralization - in the case of decapitation brain activity (and any
resulting lack thereof) is basically mediated by the lack of oxygen to
the brain caused by blood loss (hypovolemic shock).  Given that the
loss of oxygen happens at a fairly catastrophic rate with this type of
injury, unconsciousness is swift.  Brains are otherwise centralized
enough to keep on working, so it's not surprising that experiments
that intentionally attempted to maintain blood flow (or otherwise
continue oxygenation) prolong this.  But this is not dependent on
varying degrees of nervous system centralization in vertebrates - all
vertebrate brains should continue to work if successfully provided
with the required molecular "nutrition", with dogs, chickens, royalty,
and hagfish all more or less responding similarly under those
circumstances.

This is the opposite of the issue of body coordination without the
brain, where continued centralization of the nervous system in mammals
leads to a different result than that seen in diapsids (and explains
why I would expect non-fowl theropods like Ornitholestes to exhibit
similar degrees of coordination as seen in extant ones).

It turns out brains are over rated:

http://en.wikipedia.org/wiki/Mike_the_Headless_Chicken