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Taxonomy (was Re: Fixing dinosaurian carnivour question)



On Thu, 27 May 1999 Dinogeorge@aol.com wrote:

> Taxonomists seem to overlook the fact that once clade A is defined, and clade 
> B within clade A is defined, one can unambiguously define a taxon A-B by 
> subtracting (removing) clade B from clade A. This is what cladists are forced 
> to do when they talk and write--informally, of course--of "non-avian 
> dinosaurs." If mammals are found to nest within Reptilia, one could still 
> define the >class< Reptilia as the >clade< Reptilia minus the >clade< 
> Mammalia (which = class Mammalia).

But then one would have to specify which version of Reptilia they were
referring to every single time they used the word.

> There is no subjectivity in such paraphyletic definitions except as
> concerns which clade to subtract from which and how the taxa thus formed
> should be ranked; but this kind of subjectivity is precisely the same as
> the kind that attends the naming of "important" clades versus not naming
> "unimportant" clades in a strictly cladistic taxonomy wherein all the
> taxa are clades (monophyletic) and ranking, if any, is done by
> inclusion. 

BUT phylogenetic taxonomy *recognizes* all clades as being valid taxa,
even if all are not named. Traditional taxonomy does not recognize
anything unnamed as valid, and only names relatively few clades and
paraphyletic taxa, all of which are arbitrarily picked. If you want a
taxonomic system which includes both monophyletic and paraphyletic taxa to
have the same objectivity as PT, it would have to recognize *all*
monophyletic *and* paraphyletic taxa as valid (even if it did not name
them all).

> Where cladistic taxonomists and I really part company is over the idea that 
> taxa must >only< be clades. This arbitrary rule, along with differentiating 
> stem-based and node-based definitions, results in a truly unnecessary 
> proliferation of taxonomic names ("dinosauromorpha," "eudinosauria," 
> "eusaurischia," etc., etc.), so that we ultimately wind up with more 
> higher-level taxa than we have species to be classified: like having seven 
> managers for five workers.

Four, going by membership. But a para- and monophyletic system as
objective as PT would have 29 (again going only by memberhip).

Once you start getting into the nitty-gritty it's really NICE to have a
lot of precise terms. In a post yesterday I was rather frustrated by the
LACK of names for certain clades (namely {_Oviraptor_ + Neornithes} and
{_Oviraptor_ > Neornithes}).

And another great thing is that it *is* possible to delineate paraphyletic
groups very precisely by explicitly stating which clade or clades has/have
been excluded, as in phrases like "non-avian dinosaur" or "non-hominine
animal" or "non-mammalian amniote" are whatever other paraphyletic
group you may wish to discuss.

--T. Mike Keesey                                    <tkeese1@gl.umbc.edu>
WORLDS                                  <http://www.gl.umbc.edu/~tkeese1>