re: Defining Ornithischia 2

[david peters <davidrpeters@earthlink.net>]

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