Re: Eponymous Taxa [was: RE: new _Scleromochlus_ ref]

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

        "A rose, by any other name, would smell as sweet."  - Wm. Shakespeare

At 11:12 AM 9/22/99 -0400, Tim Williams wrote:
>>           Pseudosuchia
>I wish someone would perform the last rites on this silly old name.  As has 
>pointed out before (and published by someone in JVP, not too long ago), the 
>name is highly inappropriate.  The Pseudosuchia, as currently defined, 
>includes (among other assorted archosaurs) the Crocodilia.  We have a 
>situation where the Crocodilia (true crocodiles) is contained within the 
>Pseudosuchia ("false crocodiles").
        In the early years of the explicit application of the principles of
phylogenetic systematics to taxonomy, there was a problem. Simply put, what
does one do with paraphyletic taxa? At that time, although it was recognized
that taxa needed to be monophyletic, traditional typological concepts of the
definition of taxon names prevailed. Was a paraphyletic taxon to be
abandoned because its "taxon concept" was no longer considered valid? I do
not know how much discussion there was of this, but there must have been
some. How many times has someone told you that "reptilia doesn't exist"?
        Along came DeQuiroz and Gauthier, with the framework for an entirely
new, non-typological approach to the naming of names. These authors
established the fundamentals of a new taxonomy based on common ancestry.
Phylogenetic taxonomy was not concerned with "taxon concepts." It redirects
systematics from the search for the validity of groups of organism formed _a
priori_ of an analysis, to the discovery of the natural attributes (e.g.,
content, diagnosis) of clades already known to exist, but named _a priori_.
        Within such a context, and given an already established typological
taxonomy, it must have seemed easiest to these authors to adapt the
traditional taxon names to the new system. Indeed, they took it as given
that this would be done, and they provided a criterion for determining the
appropriate names: the first association of a taxon with a particular common
ancestor would be considered the correct name. For taxa which were
more-or-less monophyletic to begin with, this was not as much of a vexing
issue (except in the case of clades which included extant members, in which
case the divisive issue of "crown" clades continues to draw sometimes
aggressive comment). However, for traditionally paraphyletic taxa, this was
something of an issue, as the name was originally associated with a
paraphyletic group.
        Three options seem immediately clear. In all cases it should be
noted that traditional taxonomists would not be happy since the new taxon
would not conform to its original "concept":

1)      Apply the traditional name to the common ancestor of the
paraphyletic group and all of its descendants. This would, of course,
include traditionally excluded taxa, but would be true to a holistic
application of the principle of common ancestry and descent, and would, to a
certain extent, grant access to the literature, if only by retaining a
traditional taxon name.

2)      Apply the traditional name to a monophyletic subset of the original
group. This would greatly reduce the scope of the taxon, and inhibit access
to the literature a bit more than option #1, but does not involve as large
an "error" in taxon content (because any six-year-old knows a bird isn't a
dinosaur!). This is a less ideal option under DeQ&G's original conception of
PT, since it associates the taxon with a new ancestor.

3)      Discard the name and create new taxa as necessary.
        
        Note that both options 1 and 2 treat the original taxon almost as if
it were already a phylogenetic taxon which has been incorrectly assessed due
to improper phylogeny or methodology. There are therefore arguably more
preferable as they are consistent with PT as a whole. Option #3 treats taxa
as typological constructs formulated on a "concept"; the taxon being void
because the "concept" of paraphyletic taxa must inherently be fallacious.
        Option three promotes taxonomic proliferation. The accusation of
that crime having already been levelled against "cladists" (despite ample
evidence that this is more a affliction of systematics in general than of
any particular camp), it is unsurprizing that this option was eschewed by
Gauthier and other early practitioners of PT.
        The same thought process which lead to the principles behind option
#1 lead to the adoption of Pseudosuchia. Subsequent attempts to discard this
usage as "inappropriate" (e.g. by Sereno and Benton) have been rightly
dismissed (Padian and May 1993). An inappropriate name is a typological
consideration, not a recognition of a real problem as regards phylogenetic
taxonomy. I think alot of taxon names are inappropriate (anything beginning
with "Eu-" or "Neo-", for example). However, in PT, a name is a name. The
name can be sunk by priority (as Avemetatarsalia may someday be), but the
definition is what must be challenged for appropriateness. IMHO, this should
happen only in the context of priority, potential logical contradiction,
access to the literature, or failure to acknowledge a type taxon.

        So, the way I see it, you have three options:

1)      Abandon PT.

2)      Make up your own rules.

3)      Try to make the best of the situation. Maybe it does make sense that
the "true crocodyles" rose from among the "false crocodiles". It may seem
sinful for a cladist to say this, but does *everything* have to be an
exclusive dichotomy?

        :)

        Wagner
--------------------------------------------------------------------------------
     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