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RE: ORNITHISCHIANS :-)



I would strongly recommend not disbanding familiar groups like Thyreophora,
Cerapoda and especially Ornithischia in your phylogenies.  George's is an
EXTREMELY minority opinion and is almost completely without support.
Thyreophorans are united by several characters besides "keeled armor
scutes", if you for some reason doubt the usefulness of this character.  I'm
no ornithischian expert, but Huayangosaurus has two rows of parasagittal
keeled scutes, very similar to ankylosaur scutes.  Add that to the cranial
characters listed by Pete and you have pretty strong evidence for a
monophyletic Thyreophora.  On the other hand, there has only been one
character presented that would support a stegosaur-cerapod group- the
completely perforate acetabulum.  If you actually look at the distribution
of closed acetabula in ankylosaurs, you will see that basal forms
(Scelidosaurus, Minmi, Mymoorapelta) have only partially closed acetabula,
while more derived forms (Polacanthus, nodosaurids, ankylosaurus) have
imperforate acetabula.  But no one has noted that the supposedly basal
ankylosaur Scutellosaurus has a completely perforate acetabulum.  This
pretty much proves that ankylosaurs were reducing their acetabulum, not
retaining the primitive condition from a semiperforate ancestor.  Now George
has claimed to have other characters to support this arrangement, but has
not made them public.  I think we can all agree that changing a
classification based on undisclosed evidence is not good science.  Look at
the literature (and specimens if you're lucky), try to find evidence against
the orthodox phylogeny, but don't doubt it based on one person's unpublished
data.  I think Jon Wagner's warning against the trustability of abstracts
goes a long way in this example.  All of this is even more applicable to
Tracy's comment on ornithischian polyphyly.  I'm sure it was just meant as
an example to question accepted phylogenies more and not as an actual
theory.  There are MANY characters supporting a monophyletic Ornithischia
and stegosaurs certainly exhibit them.  I don't believe it has ever been
seriously entertained in the literature that Ornithischia is polyphyletic.
Ken is right to be scared about such a suggestion, as it really is
completely without evidence.  Of course, if Tracy actually has evidence, I'd
be happy to consider it, but I feel he was simply using it as an example, as
said before.  Ornithischia is supported by more than just a predentary and
opisthopubic pelvis (at least post-Pisanosaurus ornithischians) after all.
So, just to sum up, don't make more polytomies than you have to because of a
couple people's unsupported (in the literature, including this forum)
theories, we have enough real polytomies in this business as it is. :-)

Mickey Mortimer