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Re: Taxonomy (was Re: Fixing dinosaurian carnivour question)



In a message dated 5/27/99 10:30:17 PM EST, tkeese1@gl.umbc.edu writes:

<< 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.>>

By no means. The idea is to pick one >and stick with it<.
 
<<> 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).>>

Heaven knows what the word "valid" has come to mean in this context. 
Certainly every clade is >real<, but it's only potentially valid as a taxon 
until it has been given a name, definition, and diagnosis.

<< > 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).>>

Don't forget stem-based versus node-based definitions. And character-based, 
too, although these aren't held in as high regard these days. Considerably 
more than four; that's just the number of branch points in a tree for five 
species.
 
<< 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}).>>

Your notation is all that's really necessary to specify any clade. Add 
subtraction and you can specify any group you want without having to make a 
formal taxon out of it. Formal taxonomy should be reserved for the 
interesting and important groups, such as they are. The ones people keep 
using in their papers and discourse.
 
<< 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. >>

I prefer "dinosaur" to "non-avian dinosaur" every time. Also, I like the 
handy partitioning aspect of Linnaean taxonomy: each taxon divided into 
nonoverlapping subtaxa. That kind of thing is lost in strictly cladistic 
taxonomies. But that's more a matter of personal preference. A lot of this 
debate is theological rather than scientific. Like I said, you can please 
some of the people all of the time...