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