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Re: Fwd: RE: ORNITHISCHIANS :-)



Ken Kinman wrote:
> 
> Dear All,
>      Tracy asked me to forward the post (down below) to the whole list.
>      I was a little surprised at first, but I guess it is a question that
> should be considered.  I'm not sure why stegosaurs in particular might be
> classified outside of an ornithischian clade, but if they were, I think
> ankylosaurs would probably have to be classified separately as well.
>      I'm not sure, but are you suggesting that the predentary might have
> evolved independently in two or more lines (stemming from different groups
> of primitive dinosauromorphs?   I've never really considered that
> possibility----I guess it is possible, but doesn't seem very parsimonious.
> But then again, before last weekend I knew very little about ornithischian
> phylogeny, so I am a relative "newbie" on this subject.  Will have to roll
> the idea of a "polphyletic ornithischia" around in my head.   But if it is
> polyphyletic, that is kind of scarey.  If the interrelationships of just
> three major groups of dinosaurs is problematic, think how messy it would get
> if we had even more independent groups to consider.
>                    -----Cheers,  Ken
> *********************************************************
> >From: "Tracy Ford" <dino.hunter@home.com>
> >To: <kinman@hotmail.com>
> >Subject: RE: ORNITHISCHIANS :-)
> >Date: Wed, 13 Jun 2001 13:20:25 -0700
> >
> >
> >-----Original Message-----
> >From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> >Ken
> >Kinman
> >Sent: Wednesday, June 13, 2001 6:01 AM
> >To: dinosaur@usc.edu
> >Subject: Re: ORNITHISCHIANS :-)
> >
> >George,
> >      I wouldn't go so far as to suggest that Thyreophora (sensu lato) is
> >polyphyletic.  I have a feeling that it is neither holophyletic nor
> >polyphyletic, but simply  paraphyletic (and therefore a natural group for
> >traditional eclecticists).  Right now I would say that armor in stegosaurs
> >and ankylosaurs is probably something that is neither pure convergence nor
> >pure parallelism, but something in between (since convergence and
> >parallelism can grade into one another, and distingushing between the two
> >may be next to impossible given an incomplete fossil record, and could be
> >an
> >arbitrary distinction in any case).  However, I certainly agree with you
> >that using armor as a synapomorphy is definitely a bad idea.  However, if
> >you could find synapomophies for a stegosaur plus ornithopod clade, I would
> >certainly consider them, but I strongly doubt that such a clade exists.
> >      I am presently inclined to classify thyreophorans (sensu lato) as
> >paraphyletic (two separate, but adjacent clades) as follows:
> >ORDER ORNITHISCHIFORMES
> >      1  Pisanosauridae
> >      2  Lesothosauridae
> >      3  Plesion _Scutellosaurus_
> >      B  Aykylosauridae (incl. Scelidosaurus)
> >      4  Plesion Emausaurus
> >      B  Stegosauridae (incl. Huayangosaurus)
> >      5  Thescelosauridae
> >      6  Plesion Agilisaurus
> >      7  Plesion Echinodon
> >      8  Heterodontosauridae
> >              ...and so on for other ceropodans....
> >
> >Why does Stegosaurus HAVE to be an ornithischian? Just look at the
> >diversity
> >of life today. Stegosaurs, and other dinosaur groups for that matter, may
> >not be as closely related as is thought. We have hundreds of million's of
> >years of evolution and trying to classify them. And they all may not be as
> >closely related.
> >Tracy L. Ford
> _________________________________________________________________
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   Hmmmm, sounds like a ready and waiting Master's Thesis if anyone is
up for it!

  David Krentz