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Re: ORNITHISCHIANS :-)



In a message dated 6/14/01 3:05:11 AM EST, Mickey_Mortimer11@email.msn.com 
writes:

<< > Stegosaurs represent a distinct branch of Ornithischia that may or may 
not
 > have anything to do with the ankylosaurs. They differ from ankylosaurs in
 > practically all aspects of their skeletal anatomy, so if they do share a
 few
 > minor similarities these may or may not be meaningful.
 
 This statement doesn't make sense.  It doesn't matter how different taxa
 are, just what derived characters they share (no matter how minor). >>

What I'm saying is that since so many stegosaurian characters are 
autapomorphies, it is quite possible that a few characters here and there 
could have evolved independently and coincidentally to resemble characters in 
other, distantly related, groups. In other words, the apparently shared 
characters could have appeared by long-branch convergence rather than via 
common ancestry. If there is long-branch convergence, then the resulting 
shared characters are not evidence of common ancestry.

It's fine with me if you hang your hat on the characters that ankylosaurians 
and stegosaurians do share and unite the groups as Thyreophora. But I still 
regard ornithischian phylogeny at this level as unresolved.