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Re: Vertebral spines on sauropods...



At 10:50 AM 12/11/98 -0500, Norm King wrote:
><<Admittedly, the neural spines of _Amargasaurus_ are ridiculously
>long, but is there any actual precedent to back up the assumption that
>they form the bony core of "spikes"? What animal -- living or dead --
>has such a structure?>>
>
>Amargasaurus?
>
>(That's like asking what animal, living or dead, has plates on its back 
>like stegosaurus?)

I think what Brian (or Jaime?) was asking was whether the neural spines each
emerged as a separate spike out of the fleshy part of the neck of
_Amargasaurus_.  This is not known directly from the fossils, and is one of
two commonly suggested model.  I can't think of any living animal in which
we can demonstrate a neural spine forming an isolated spike.

The other model is that the spines contributed to a pair of sails (a right
and a left) down the neck of the _Amarga._, as sort of a double-barrelled
_Dimetrodon_.  In this case the spines have connective tissue fore and aft
to the next neural spine over most of their height. 

>< I may be mistaken, but aren't the neural spines flattened, and not
>round?

The more anterior ones are rounder (and slender); the more posterior become
flatter on the sides.

><Wouldn't this make spikes less likely, as a flat bone would
>tend more to bend than a round one, and therefore less effective in
>any form of combat or intraspecific interaction?

As Norm King mentioned, intraspecific interaction is often visual, and don't
involve physical contact.

><A flat spine would be
>more useful, I'd think, for supporting a sail, as originally assumed
>(Coria and Salgado) but I may be wrong there.>

That was the original assumption (although it was Salgado & Bonaparte:
credit where credit is due, and all that...).

>I thought that at least some of the spines of Amargasaurus are forked at 
>the top, as if they supported a dorsal ligament for support of the neck.

No, the cleft goes all the way down to the base of the spines (at least for
the cervicals).  Like all diplodocoids, their neural spines (which are a
single bump or spine in most animals, like ourselves) are cleft into right
and left halves.  This cleavage goes from the top all the way down to the
main body of the neural arch.
 
>If so, the spines must have been connected by a skin membrane (or were 
>there holes through the "sail"?

As I interpreted it, that was Brian (or Jaime's?) original question: was it
a sail, or was it a bunch of individual isolated spikes.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661