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

Since I'm briefly coming out of list retirement today I wanted to
address the issue of headless chicken running a bit.  While the idea
to put it in the show was not mine, David certainly mentioned it to me
and I did not shoot it down (and still wouldn't).  I'll grant you that
there isn't much in the professional literature on the subject, but I
think people are thinking of this from the wrong way (i.e., wondering
about the distribution of "headless-running" in birds like it's a
derived condition).

Vertebrates as a group have one of the more centralized nervous
systems among animals (with some arthropods and especially some
cephalopods as the other contestants in the "flexibility over
redundancy sweepstakes"), but tetrapod nervous system evolution in
general is a story of progressive centralization that (so far)
culminates in mammals.  Even in humans, with our gobs of ridiculously
calorie-hungry centralized gray matter, we still have autonomous
reactions that don't require the brain to be involved (as anyone knows
who's burned themselves and jerked their hand away before they felt
the pain).  That said, we have gone a long way down the path of
nervous system centralization, and if you cut a mammal's head off you
may get some twitching but it won't run around; our limbs literally
cannot coordinate themselves without the brain's involvement (although
morbidly it does appear that the head itself retains some
coordination, if medieval reports are true that people were employed
to read lips for up to a minute after a beheading).

This degree of centralization is the derived condition, not the
primitive one.  So I doubt chickens are special here, except in as
much as they more frequently get clean beheadings in the presence of
human observers than most other birds (a quick Google search shows
that turkey's exhibit this as well).  This should be true of lizards,
crocs, etc too (diapsids as a whole).  With enough experimental trials
I'd fully expect an Ornnitholestes to do a good headless chicken
impression.  Now, I'll grant you that this would require a pretty
clean bite on the allosaur's part, and the odds of observing it in the
wild would not be very high.  But the sequence was created to be a
surprising bit of humor in a scenario that was possible, not probable.
 Given those parameters it seems reasonable enough to me.


Scott Hartman
Scientific Advisor/Technical Illustrator
(307) 921-9750
website: www.skeletaldrawing.com
blog: http://skeletaldrawing.blogspot.com/