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Phylogenetic Taxonomy of the Sauropoda



        As a demonstration of the new Buchholz-Wagner shorthand for
phylogenetic taxon definition, I have prepared a summary of the taxa defined
in Wilson and Sereno 1998. I have split definitions after the first three
elements and indented the rest on the line below to make reading easier.

Sauropoda == { _Saltasaurus_ > _Plateosaurus_ }, 
        Marsh 1878: def. Wilson and Sereno 1998
Eusauropoda == { _Saltasaurus_ > _Vulcanodon_ }, 
        Upchurch 1995: def. Wilson and Sereno 1998
Neosauropoda == { _Diplodocus_ + _Saltasaurus_ }, 
        Bonaparte 1986: def. Wilson and Sereno 1998
Diplodocoidea == { _Diplodocus_ > _Saltasaurus_ }, 
        Marsh 1884: def. Wilson and Sereno 1998
Macronaria == { _Saltasaurus_ > _Diplodocus_ }, 
        Wilson and Sereno 1998
Titanosauriformes == { _Brachiosaurus_ + _Saltasaurus_ }, 
        Salgado, Coria and Calvo 1997: def. Wilson and Sereno 1998
Brachiosauridae == { _Brachiosaurus_ > _Saltasaurus_ }, 
        Riggs 1904: def. Wilson and Sereno 1998
Somphospondyli == { _Saltasaurus_ > _Brachiosaurus_ }, 
        Wilson and Sereno 1998
Titanosauria == { _Saltasaurus_ > _Brachiosaurus_, _Euhelops_ }, 
        Bonaparte and Coria 1993: def. Wilson and Sereno 1998

                        SOAPBOX TIME:
A few notes on the treatment of phylogenetic taxonomy by Wilson and Sereno...
        1) The authors do not explicitly state whether they are applying a
definition or providing a definition for a taxon previously lacking one (if
they were familiar with our scheme, they might have thought of this ;).
Thus, I am assumed above that all definitions were new as of the monograph,
and retain priority.
        2) The authors word definitions in a manner which is somewhat
problematic, although still readily interpretable. Whenever possible,
extraneous elements have been filtered out in the above listing. For
example, Brachiosauridae is defined as "Titanosauriformes more closely
related to _Brachiosaurus_ than to _Saltasaurus_..." followed by a list of
included taxa. The list of included taxa is extraneous. The specification
that the taxon consists of members of Titanosauriformes, while it is
certainly seems true, is also extraneous. Under different circumstances
similar usage might result in logical difficulties, such as if a different
definition of Titanosauriformes had priority. Also, "sharing a more recent
common ancestor" is probably preferable to "more closely related", even if
the two mean the same thing in a phylogenetic context. Picky, picky me.
        3) The authors continue an earlier assertion of Sereno (1997) that
node-stem triplets constitute a more stable taxonomic structure than other
taxonomic arrangements. They fail to note that this will *only* be the case
when the node-based taxon and both stem-based taxa share the *exact* same
[preferrably genus- or species-level] anchor taxa (obviously, in differing
roles). I call this particular combination the "conjugate-conjoined
node-stem triplet". Additionally, for this to be stable, all three
definitions must have priority.
        4) The authors make the "Gauthier gaff" of anchoring a supergeneric
taxon which bears the name of a genus with a taxon other than that
particular genus (e.g. Ornithosuchia == { Neornithes > Crocodylia } ). There
is no gauruntee that the Titanosauria or Titanosauriformes which they have
named will include Titanosaurus. This may lead to problems with access to
the literature (not to mention enflaming Jonathon Woolf). From what I hear,
_Saltasaurus_ is kind of an oddball, and not a good place to look for your
standard titanosaur. IMHO, converting from a typological taxonomy to a
phylogenetic one, we get one chance to apply our typological concepts within
a phylogenetic framework. We can only say once "we all know what a
titanosaur is, let's make sure the phylogenetic definition fits." After
that, the gig is up.
        5) One is forced a bit to worry about access to the literature when
reading definitions of "family rank" taxa. While PT does not acknowledge
rank, there is a typological notion that we all know what "families" are,
and what should be in a "family". I think most people would be rather upset
to find out someday that _Diplodocus_ is a brachiosaurid (it could happen, I
guess...). Heck, if _Saltasaurus_ is a basal sauropod, all of our favorite
BUFFs might become brachiosaurids. Access to the literature might be
seriously impaired. This is part of the deal with PT, and is to be expected.
However, by the simple expedient of selecting either a node-based definition
of the taxon, or by using a stem-based definition including several
exclusive anchor taxa (e.g. == { _Brachiosaurus_ > _Diplodocus_,
_Titanosaurus_, _Camarosaurus_, _Euhelops_, _Saltasaurus_ } ), such problems
might be resolved. Or might not...
        6) Wilson and Sereno are to aplauded (some would say jeered) both
for their consistant use of generic anchor taxa (rather than supergeneric
taxa), and for their use of multiple exclusive anchor taxa in a definition
(maybe that should be an academy award (R) ;).

        Wagner

----------------------------------------------------------------------------
    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
    "See that lump on his jaw? ...it's called 'lumpy jaw'" - Steve Irwin