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Re: "Phylogenetic Definitions and Nomenclature..."



At 02:16 PM 3/26/99 -0800, Nick Pharris wrote:
>What's wrong with multiple exclusive anchor taxa?  They allow you to
>define more explicitly exactly the taxon you want to describe, especially
>when dealing with unresolved polytomies.
        Is is just me, or has the tenor of the dinosaur list become a little
strained recently?
        That was a sigh of relief, Nick old buddy. As you may recall, I've
been thumping the Hennig '56 on M.E.A.T. for several years now (who coined
the term "anchor taxon" anyway? Personally, I take credit until someone
proves me wrong... check the archeives :). Actually, they are more
advantageous when trying to restrict the content of a previously
non-phylogenetic taxon during definition, in the hopes of better assuring
access to the literature. As for unresolved polytomies, this is taken care
of in the definition.
        For example, if you topology is: (((A, B), C, D), E), and your taxon
is defined as X == { A > E }, then which taxa are included within X? Answer:
well, A and those taxa sharing a more recent common ancestor with A than
with E in this topology, i.e. B, C and D. Now, if Y == { A > D }, which taxa
are in Y? Well, A, and those taxa sharing a more recent common ancestor with
A than with D, i.e. B. C is not included, because, given your topology, it
is not hypothesized to share a more recent common ancestor with A than with D.
        Now, M.E.A.T. are useful if we are trying to phylogenetically define
the elusive Aidaem, a taxon which is traditionally considered distinct from
the Bidae, the Cidae, the Didae and the Eidae. In this case, a definition of
Aidae == { A > B, C, D, E } will ensure that this state continues. This
could, for example, keep _Troodon_ out of the Dromaeosauridae.
        
        :)
        Wagner
--------------------------------------------------------------------------------
     Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
 "Only those whose life is short can truly believe that love is forever"-Lorien