re: Defining Ornithischia 2

[William_Parker@nps.gov]

I would be interested in seeing lists of synapomorphies supporting the
inclusion of these taxa into "paraornithischia" besides the calcaneal spur
and the presence of a predentary (and showing that these structures on all
included taxa are homologous).  The placements that you question have been
defended in several phylogenetic analyses and there is no need to defend
them any further at the present time.  You need to provide synapomorphies
'defending' your hypothesis that these placements are erroneous.


************************************************************************
Bill Parker
Vertebrate Paleontologist
Division of Resource Management
Petrified Forest National Park
P.O. Box 2217
1 Park Road
Petrified Forest, AZ 86028
(928) 524-6228 x262


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  |       Subject:  re: Defining Ornithischia 2                                 
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If anyone wants to defend the placement of Lotosaurus within the
Rauisuchia, or Effigia within the Crocodylomorpha, or Silisaurus within the
wastebasket taxon, Dinosauromorpha, reach me here. I'd like to hear what
you have to say. (Yes, I've seen Irmis et al. 2007 and it has problems
galore.)

Those taxa became nested where they became nested because there was no more
attractive pairing for PAUP to discover among the 175 participants in my
analysis. Frankly, I don't care where they end up. I just report the
findings. And they are robust.

re: the tarsus in Lotosaurus and Effigia: like all archosaurs
(=crocodylomorphs + dinos) it had bipedal ancestors with small,
comma-shaped calcanea (ala Turfanosuchus). As in derived crocodylomorphs,
and unlike most other dinos, that spur expanded along with the evolution of
quadrupedality. Or, in the case of most dinos, it disappeared. But you can
still see a remnant in some prosauropods and Pisanosaurus.

re: the predentary. Well, it had to start somewhere. By the evidence of
Sacisaurus and others, it had a paired origin. That the pair is no longer
plainly visible as a separate ossification in some taxa, like Lotosaurus,
has precedence in any number of bones which lose their individual identity
through fusion with a neighboring bone. Nesbitt's dentary on Effigia is
topographically the paired predentary, for instance, and his extended
surangular is the result of fusion with the toothless dentary.

The term paraornithischia would refer to a (perhaps paraphyletic, it's too
soon to tell) clade 'beside' the traditional ornithischia. I would suggest
that the term Predentata become resurrected for the rest of the
ornithischians having a fused predentary. If you've ever wondered what
ornithischians looked like before they had predentaries and retroverted
pubes, well, you're looking at'em when you see Lotosarus and Silesaurus.
They're not exactly like their traditional cousins. But currently there's
no better place to put them.

Or is there? Let me know.

David Peters
St. Louis
davidrpeters@earthlink.net