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



On Fri, 28 May 1999 Dinogeorge@aol.com wrote:

>  > 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<.

Then how can you refer to "Class Reptilia" and "Clade Reptilia"?

> > 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. 

By valid I mean that it is recognized as a real taxon and can be named. In
Linnaean taxonomy if Coelurosauria is (let's just pick some rank here) an
infraorder and Oviraptorosauria is a parvorder (if I have that prefix
right), then Maniraptora cannot be named -- there's no room for it. PT,
OTOH, always has enough room to accomodate new discoveries and hypotheses.

> > > 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.

I was just trying to keep the math simple. Remember, for every clade we
add, that's five (I think) more paraphyletic groups that must be added to
the para/monophyletic system. 

> And character-based, 
> too, although these aren't held in as high regard these days.

That's putting it mildly.

> << 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.

Then we can dispense with any higher-level taxonomies. I give you the
{_Triceratops_ + Neornithes} Mailing List! (Or perhaps some would prefer
the {_Triceratops_ + Neornithes} - {_Archaeopteryx_ + Neornithes} Mailing
List.)

> 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.

I think the two I mentioned are pretty interesting.
  
> << 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.

And do you prefer "avians and dinosaurians" to "dinosaurs" every time? (Or
should that be "avialans and dinosaurians", given your usage of "Aves"?)

Why is it so much more useful to refer to this particular paraphyletic
taxon than to another paraphyletic taxon? Why should Dinosauria exclude
Aves as opposed to Neornithes, or Ornithothoraces, or Tetanurae, or
Coronosauria and Iguanodontoidea and Thyreophoroidea and Sauropoda?

> 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.

Perhaps I'm missing your point, but phylogenetic taxa *are* divided into
non-overlapping subtaxa.

> 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...

I suppose it can be chalked up to personal preference -- some prefer
objectivity and precision to subjectivity and vagueness.

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