Re: Stegosaur plates as protection......

["Mark Sumner" <range@inlink.com>]

The defensive role is, of course, the original interpretation of the plates
on stegosaurs.  It was only in the 70's that their role as a possible
thermoregulator was expounded.  The relatively fragile nature of these
plates, and their "weak" attachment to the rest of the skeleton bolstered
the anti-armor camp.

But I'm something of a traditionalist when it comes to stegosaurs, and I
think the argument advanced in the last couple of messages is a strong one.
  The plates on Kentrosaurus and Lexovisoaurus (among others) are as
"loosely attached" as those on S. ungulatus, but their shape, and relative
lack of blood vessels, argue that they would have had a very limited effect
on thermal regulation.  On the other hand, they appear to be fairly
convincing defensive armor.

We're then faced with stegosaur plates that form one function in one
species, and a completely different function in another.  And we're stuck
with the idea of thermoregulation carried out, at least in part, by running
blood through the inside of bony plates -- a very odd adaptation that's
quite different from other sails, frills, etc. which (supposedly) serve
this purpose.  It's far from impossible, but I'm not sure that the existing
evidence is enough to shove me onto the heat-exchanger side of the "razor."

I suspect that the plates on S. armatus, S. ungulatus, S. yournamehere, and
Diracodon (for those who believe), might actually represent something
similiar to "horn cores," which in life would have sported hard sheaths. 
Perhaps those in "spiny" stegosaurs like Kentrosaur were also equiped with
sharp extensions.  Attacking a critter with a back covered in razor blades
seems like a bad idea.

Mark Sumner
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