Re: Stegosaur plates as heat exchangers

[Nick Longrich <longrich@phoenix.Princeton.EDU>]

There is actually no reason for the plates not to regulate heat *and* work
for defense *and* display. Ungulates use their horns for all three. I am
told that bighorn sheep (the species we were discussing at the time) can
send blood to or restrict blood flow from their horns to either radiate or
conserve heat. Stegosaur plates were likely highly vascularized and have a
much better surface-area to volume ratio and there are a heck of a lot
more of them. Even the relatively slender spikes of many species would
have had a lot of surface area and a lot of potential to heat up or cool
down the animal. It's perfectly consistent with warm-blooded dinosaurs
AFAIK, too though I don't know if it argues one way or the other. And
perhaps it was poikilothermic, too- camels are supposed to be able to heat
up and cool down the body or something like that. Bighorn sheep, of
course, use their horns in several ways and illustrate the sort of
swiss-army functonality of some parts of anatomy. The horns are used for
butting, of course, but also allow males to size one another up before
going for a fight, and so are part of display, and they can also radiate
heat in the summer (in the winter just a trickle of blood goes through).
Who knows. 

On Fri, 13 Jun 1997, Joshua Dyal wrote:

> One thing that bothers me about the idea of Stegosaurus using his plates
> as heat exchangers are the plates of closely related genera.  Maybe
> someone on this list can help me clear it up, or settle it in my mind at
> least.
> 
> OK.  Stegosaurus stenops does have very broad, large plates with a lot
> of surface area that could have worked well as heat exchangers. 
> However, S. ungulatis has much narrower and smaller plates that wouldn't
> have worked nearly as well.  Huayangosaurus, another setgosaur, had very
> thin, pointed plates, that resembled spikes more than solar panels.  And
> finally, Dacentrurus, another stegosaur, had no plates at all-- just
> spikes all the way up his back.
> 
> So S. stenops had plates that could have made good heat exchangers, but
> the examples I gave got progressively worse until Dacentrurus, who
> couldn't have used his spikes for anything other than defense.  If all
> of these genera are supposedly closely related, wouldn't it be extremely
> odd that the plates (or spikes in Dacentrurus' case) would be used for
> such diverse functions as defense in one genus and heat exchange in
> another?  To me, this seems like very strong indirect evidence that even
> big plated stegosaurs like S. stenops must have used the plates for
> defense, but it seems most paleontologists preach the heat exchanger
> doctrine.  This doctrine seems (to me, at least) to use S. stenops as
> its model while ignoring other stegosaurs that would have been quite
> inefficient at heat exchange with their narrow plates, that had very
> little surface area relative to big plated stegosaurs.
> 
> Anyway, I've said my piece.  Now its up to everyone else here to show me
> why I'm wrong.  I do want to know why it is that experts keep saying
> that the heat exchanger idea is the preferable one, but I can't for the
> life of me, buy into it.
> 
> Joshua Dyal
> j-dyal@geocities.com
>