Stegosaurus, plates, spikes...

[tlford@ix.netcom.com (Tracy Ford)]

I'm more a lurker now, than I was before. Mainly because I grow weary of 
banging my head aganst the wall, or so to say. But I couldn't let this go with 
out saying something...

>Stephen Czerkas has played around with "real" stegosaur spikes and caudal
>vertebrae, too, and reached an interpretation of his own.  At his talk,
>Czerkas pointed out that, although these spikes are sometimes preserved in
>the now-familiar flattened, posteriolateral horizontal orientation (as seen
>in the DMNH 2818 specimen), other specimens preserve the pairs of spikes
>one atop the other -- suggesting paired vertical tail spikes. 

But he didn't explain what filled in the gap between the bottom of the spikes 
and the vertebrae if the spikes were held in there 'traditional' angle. If the 
spikes were held horzontally, at the main part of the spike arou
nd the center of the caudal vertebrae, the spikes could be held more firmly. 
Unlike how Czerkas had it in his talk, at the top of the caudal neural spines.


>
>On the subject of _Stegosaur_ plates, Czerkas pointed out that even if the
>base of the plates emanated directly from the midline of _Stegosaurus_,
>some amount of each plate (the "root," I might call it) would be buried
>beneath the skin, resulting in some gap between the plates on the exterior
>of the animal.  But, as Pete Buchholtz has already stated, Czerkas
>interprets _Stegosaurus_ as having perhaps some lateral spacing between the
>bases of the plates as well (in contrast to his earlier position on the
>subject: see _Dinosaurs: A Global View_, page 142).     
>
He's still on this track. The primitive condition (and I really don't give a 
*&^%$ if that is the wrong term) a double row of osteoderms. Early 
pseudosucians, crocodilians, dinosaurs (Sctullosaurus has two row of osteoder
ms on it's back not a single row running down the midline of its back, so does 
Scelidosaurus, stegosaurs, etc) so two rows of plates isn't unreasonable. 

>Czerkas' graphic comparison of the dentary of _Stegosaurus_ and that of a
>modern turtle (employed to illustrate why the restoration of stegosaurs
>with cheeks wasn't supported by stegosaur jaw anatomy) presented a
>persuasive argument. 

This is totally bogus. If you look at a turtle skull, you'll note that the 
upper jaw fits OVER the total length of the lower jaw. That is the horny beak. 
Stegosaurus dosen't have the overhang of a turtle skull. He only lo
oked at the lower jaw, but it is the upper jaw that forms the beak. Stegosaurus 
DOES have a beak at the front of the jaws, ie. premaxilla, predenatry, but 
after that, no beak like a turtle.

 He went on to recommend a reevaluation of
>hypothetical cheeks on all ornithischian dinosaurs.  I'm all for careful
>reconstruction of extinct animals, but I think that a good case can be made
>for ornithopods and ceratopians (at least) having cheeks based on
>comparative anatomy between these animals and extant herbivores.
>

Yes, this is something to reconsider and he might be right about this one.

>Back to the drawing board, paleoartists!
>
>On _Sinosauropteryx_: I was most interested in Philip Currie's
>presentation, which revealed important new information on the three
>fossilized individuals which he examined personally on three trips to China
>in the past year. 

Yes, that was a good talk, since he wasn't suppose to give a talk at all!!! He 
went to the SVP and asked if he could rebut the first talk on Sinosauropoteryx, 
and hey, it was good.

Tracy