Eponymous Taxa [was: RE: new _Scleromochlus_ ref]

["Jonathan R. Wagner" <znc14@TTACS.TTU.EDU>]

Adam Yates wrote:
>I don't have the paper with me but I'm sure it was a stem-based definition
>(ie all taxa closer to birds than to crocs). So it is equivalent to
>Gauthier's Ornithosuchia (and if you adhere to strict priority it is a
>junior synonym) but doesn't have the problem that the higher taxon doesn't
>contain it's nominal taxon.
        Much as I have always loved the term Ornithosuchia, there is a
"precedent" for supression: DeQuiroz and Gauthier (1992) note that if the
practice of using "type" taxa for higher taxa is to continue, there must be
a concerted effort to make deliberate reference to the "type" taxon in the
definition (loose paraphrase).
        Obviously, this is not always completely possible or desireable.
Padian, Hutchinson and Holtz (1999) used _Carnotaurus_ as the reference (=
"anchor..." darnit!) taxon for Abelisauridae, apparently because it is more
complete and therefore facilitates comparison. Presumably, if _Abelisaurus_
is found not to be a member of the Abelisauridae, someone will cry foul on
this rule and suggest a change.
        I think it is against the principles of phylogenetic taxonomy to
allow typological concepts to become too involved in taxon name definitions.
A phylogenetic taxon definition is a recognition of a real entity, and
should be divorced as much as possible from typological concepts of taxon
diagnosis or content. I would be strongly opposed to constant re-definitions
of taxa simply because, with changes in phylogeny, they no longer fit our
typological taxon concept (e.g. changing the definition of Aves because we
find a feathered flying animal more "basal" than _Archaeopteryx). However,
since this is a well delineated exception resulting from a conflict between
the ideal and the practical, an exception is not unwarranted. If this is
done, it should be made perfectly clear that it proceeds from a
nomenclatural conflict concerning access to the literature and "type" taxa
and not from perceptions of the appropriateness of the name. No future
"crurotarsizing" should be tolerated.
        An example closer to my heart: in definition of the hadrosauridae,
it would be somewhat problematic to use _Hadrosaurus_ as a reference taxon
since it, while being considered valid by many workers, lacks cranial
material. To my mind, the solution would be to anchor the taxon with
_Kritosaurus (= Gryposaurus) notabilis_, which is commonly (if not
universally) considered to be a very close relative. If future discoveries
were to suggest that, say, _Hadrosaurus_ were closer to _Iguanodon_ than
_Kritosaurus_, it would be appropriate to redefine Hadrosauridae and
Hadrosaurinae to ensure that the "type" taxon is included.
        Anyway, back to Ornithosuchia... well, much as I love it, I think it
may have to go. The sad thing is, it really is an appropriate name, it
simply suffers from the unfortunate problem of not including the taxon it is
named for. Ornithometatarsi [sic?] is, IMHO, an unaesthetic and cumbersome
name. D'you suppose there is already a name available which might be
construed to have priority?
        By the way, in the same paper (1992), DeQuiroz and Gauthier point
out that strict priority may not be the best answer for phylogenetic
taxonomy. Personally, I quite like the well thought-out approach applied by
Padian et al. (1999), where priority is sometimes supressed for the sake of
access to the literature. I especially appreciate the care with which those
authors approach determining which typological taxon is best adopted as a
phylogenetic taxon, their restraint in the naming of new taxa, the care they
show in trying to ensure that their taxonomy effectively accomodates
alternative phylogenies, their desire to achieve a consensus at the risk of
missing opportunities to place their "stamp" on dinosaur taxonomy, and most
importantly the careful documentation of all the choices they made. This
last point is especially helpful, as it allows others to judge their
decisions on more objective criteria (and, after all, isn't objectivity the
reason phylogenetic systematics got started?). I find this approach much
more rational than any supposed "rationale."


        Wagner
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     Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
  "Why do I sense we've picked up another pathetic lifeform?" - Obi-Wan Kenobi