Re: Def. of Ornithischia

[NJPharris@aol.com]

In a message dated 97-06-12 03:38:29 EDT, jpoling@dinosauria.com (Jeff
Poling) writes:

> >   In other words, why wouldn't a node based Predentata of the most recent

>  >common ancestor of, say, Pisanosaurus and Triceratops take precedence
since 
>  >node based taxa seem to be the underlying principle of cladistics?
>  
>     Oops, that would be the unnamed node Dr. Holtz spoke of.  I meant of
>  course whatever animal plus Triceratops would make up a node based
>  definition of Ornithischia.

Well, this is why stem-based taxa are useful.  We're not exactly sure what
the earliest-diverging member of the Ornithischia is (and discovery of a more
primitive example would screw everything up), so we can use a stem-based
taxon to include everything on the line leading from non-Ornithischians to
_Triceratops_.  And neither a node-based taxon nor a stem-based taxon can
take precedence over the other, since they include different sets of animals:
 the node-based taxon is a subset of the stem-based taxon, which also
includes animals (usually as-yet-undiscovered) on the line leading up to the
node-based taxon.

Hope this clears some matters up!

Nick Pharris
Olympia, WA