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Re: Removing segnosaurs from Theropoda



At 11:41 AM 8/29/95, Dinogeorge@aol.com wrote:
>That's only half the story. Along the lineage from thecodontians to birds,
>all the dinosaurs from brontosaurs to theropods arise as divergent side
>groups. Birds are not separate from theropods and theropodomorphs in
>BCF--they're right in the middle of it, literally.

        That is correct, as per your BCF theory.  But that was also _my_
point:  if the interdental plates extend back to the lineage that presages
theropods, prosauropods, and therizinosaurs, then you can't, as Thom Holtz
pointed out, use interdental plates as a synapomorphy for just the
prosauropods and the therizinosaurs -- instead, it's a symplesiomorphy
that's shared in both those groups _plus_ the Theropoda.  Now, as you did
clarify, "small interdental plates with respect to tooth size" could be a
synapomorphy, if the ones in theropods are considered different...but I'd
like to know what the primitive condition (the one possessed by the common
ancestor of birds, theropods, prosauropods, and therizinosauroids) was
before I'd be satisfied with a label of whichever later condition as a
synapomorphy.



Jerry D. Harris
Shuler Museum of Paleontology
Southern Methodist University
Box 750395
Dallas  TX  75275-0395
(214) 768-2750
FAX:  (214) 768-2701
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

---------/O\------*     --->|:|:|>     w___/^^^\--o

"If it looks like a duck, walks like a duck, and
quacks like a duck, then it is the sister taxon to,
but cannot parsimoniously be, the direct ancestor
to all other ducks."

                                --  _not_ W. Hennig

---------/O\------*     --->|:|:|>     w___/^^^\--o