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In a message dated 6/10/01 2:42:36 AM EST, Tetanurae@aol.com writes:

 Pisanosaurus has recently been shown (Sereno 1991) to be the most basal 
known member of the Ornithischia, based on, among other things, the fact that 
it's propubic.>>

AFAIK, we do not have the pubis; we have a >matrix impression< of a pubis 
that has been prepared away(!) so that only a sketch diagram remains, so that 
could well be a prepubic process rather than a propubic pubis.

<<  Before this was demonstrated however, it was widely regarded as probably 
being a member of the Heterodontosauridae, based on supposed similarities of 
the teeth.  If I recall correctly, the teeth of Pisanosaurus are rather badly 
worn, so I don't think they can be of much use in that respect. >>

They're close-packed and lack a cingulum, and quite strongly resemble the 
teeth of heteros and psittacosaurs. Detailed comparison is badly needed.

Heteros almost certainly had a Late Triassic evolutionary history, presently 
unknown or represented by a few misc teeth. It's quite likely they branched 
away from the other lines of ornithischian evolution prior to the Late