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Re: Phyl Tax roundup (was Re: Quick cladistics question)



Dr. Holtz wrote:
>Saurischia was defined phylogenetically in 1986 (by Gauthier), Ornithischia in
>1993 (by Padian and May), and Dinosauria in 1996 (by Novas).

Here's how it breaks down (see many previous posts on my shorthand):

        Ornithiscia = { + _Triceratops_, - "Birds" } (def. Padian & May (1993))
        Saurischia = { + "birds", - Ornithischia } (def. Gauthier (1986))

By Substitution:
        Saurischia = { + "birds", - _Triceratops_ } (see Padian & May 1993)

        Dinosauria = { + Saurischia, + Ornithischia } (def. Novas (1996))

By Substitution:

        Dinosauria = { + "birds", + _Triceratops_ }

----> What is wrong with this picture?
        "Birds" is *not* a taxon, phylogenetic or otherwise, rendering this
definition meaningless. Unfortunately, a "first reviewer" cannot replace
this definition with a more appropriate one on this excuse, but he could
replace "birds" with a taxon, rendering these definitions phylogenetically
applicable.
        Of course, I'm certain someone would replace "birds" with Aves,
getting into a whole new can of worms about how that should be defined
(priority clearly supports Gauthier's crown group, but then you might even
argue about how he defined that crown group...). This is fine for
Dinosauria, but could lead to paraphyly if used in the definition of
Saurischia, as multiple inclusive anchor taxa in a stem based clade are able.
        Impercision, bugbear of science.
----------------------------------------------------------------------------
      Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock TX 79409
            Web Page:  http://faraday.clas.virginia.edu/~jrw6f