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RE: ORNITHISCHIA IS VERY, VERY REAL



 

 

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of Tetanurae@aol.com
Sent: Monday, June 18, 2001 11:35 PM
To: kinman@hotmail.com; dinosaur@usc.edu
Subject: ORNITHISCHIA IS VERY, VERY REAL

 

Ken Kinman wrote:
<<The first five deal with the jaw (and plant chewing) so could have
arisen more than once.  I also wonder how many times the predentary bone may
have arisen, given its presence in at least one Cretaceous bird (EGAD!!!).>>

The ornithischian predentary is very unique among animals and in the
basal-most forms is almost identicle.  It's a base for a lower jaw beak, but
also seems to serve as an accessory joint for the two dentary rami to rotate
somewhat indepentantly of eachother (at least in the most basal forms).
<<

 

I’d think that the predentary would have made the lower jaw more solid. Snakes and lizards don’t have a predentary and they can move their lower jaws extreamly idependantly. I understand why you say that the predentary unites ornithischians and why Ken said what he said. But not all predentaries look alike. An ankylosaurid looks different than a ceratopian than a hadrosaur. No predentary has been found for a pachycephalosaur but I’d imagine that they would.



>>We also can't forget however that all ornithischians are clearly dinosaurs.  
The all have an upright gait, perforate acetabula (lost in some later
ankylosaurs), and the very distinctibe dinosaurian hand where digits 4 and 5
have no claw.
<<

 

True.

<<It's very unlikely that stegosaurs, say were really theropods, and also
evolved a strongly opisthopubic pelvis, ornithischian teeth, "cheek"
depressions, and a perdentary.
<<

 

They aren’t saying that they weren’t ornithischians, just that they may not be as closely related to ornithischians that is has been thought. They may be radically different lineages. I know we both agree that hypsilodontidae is a waste basket group and the many listed animals may have had their own ‘family’ or grouping.

<<Ornithischian phylogeny seems a whole look shakier than ever imagined,
and a paraphyletic (or even a polyphyletic) Thyreophora seems a real
possibility.>>

A paraphyletic Thyreopora could be real, but since there is no evidence to
the contrary yet presented, we have to go with the conventional view that
Thyreophora is monophyletic and excludes all other known ornithischians.

Ah, no we don’t. It’s like saying everyone is walking to the right, so everyone has to walk to the right, you can’t go left or straight because everyone is going right. We can have independent ideas and thoughts and it is from these that papers and research can be aspired (as I’m sure your working on, if not I encourge you to do so).

 

Tracy L. Ford

P. O. Box 1171

Poway Ca  92074