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Re: ADV: Re: Classification: A Definition



Graydon writes:
 > > No, no, _alpha_ taxonomy, the naming of species and genera.
 > > Those we will never get rid of.
 > 
 > I am uncertain of that.
 > 
 > Specifically in paleontology, it's unclear that species level
 > resolution is possible at all, never mind generally, so the
 > question ought to be pretty much moot.

Species or genus -- doesn't matter which, we need one of them.  I
agree that two is overkill (hence my ha-ha-only-serious suggestion of
abandoning species and retaining genera, which have the advantage of
being uninomial).  It's either specimen numbers all the way down, or
you need an arbitrary kind of taxon (i.e. not in general a clade) that
mean "this type specimen and everything else sufficiently close to it,
where 'sufficiently' must be interpreted Just Right".

 > In biology, it doesn't strike me as genera are any less artificial
 > than families or orders, or that the "epithet <namer> <date>" style
 > of species reference wouldn't work at least as well.

Totally agree.  My fondness for genera is simply that they are more
PN-friendly than specues due to the uninomial and consequent
uniqueness.  But as we all know, in the world of dinosaurs, genera and
species are pretty much the same thing anyway.

 > > Above that level I am broadly in agreement that the ranks do more
 > > harm than good -- which should not particularly suprising given
 > > that most of what little there is of my publishing record is on
 > > rank-free phylogenetic nomenclature.
 > 
 > I am unclear how the designation of a species doesn't constitute a
 > phylogenitic hypothesis.  So why are species and genera special?

Because they are defined on a single anchor specimen.  That is
pragmatically useful.

 > > The buckets would still be arbitrary, dependent to a ludicrously
 > > unstable degree on the taxon selection.  Throw another basal sauropod
 > > in there and Neosauropoda is suddenly eleven nodes down from the root
 > > instead of ten, and the hypothetical chapter-headings scheme in which
 > > we use the level-ten nodes suddenly leaves with no Neosauropoda
 > > chapter but with an unexciting
 > > Node-uniting-Lourinhasaurus-with-Neosauroda chapter.  Picking an
 > > arbitrary level is also a horrible way to go -- which is why
 > > _Dinosauria_ 2nd ed. does what everyone sane would have expected it to
 > > do, and uses chapter headings based on the "well-known" clades.
 > 
 > Not for an individual book that's trying to document a particular
 > hypothesis -- some specific tree -- it's not.

Sure it is.  No-one wants to read an article about the clade uniting
Lourinhasaurus with Neosauropoda.  Neosauropoda is a fundamentally
more interesting clade than that one, because its root is the branch
point into two major groups, rather than one group and a singleton.

 > > ... but as soon as you've nominated some clades as more
 > > well-known than others, you've done taxonomy.  We may as well
 > > admit it to ourselves.  It's certainly true that PN requires us
 > > to do much _less_ taxonomy than previously, but it doesn't
 > > eliminate it.
 > 
 > What I'm unclear on is the necessity of nominating some clade as
 > "more well-known"; I mean, yes, certainly, a clade that's received
 > a lot of study based on hundreds of specimens is better known than
 > one based on two fragmentary specimens and a single paper, but that
 > is not a stable state of difference.  (Since in principle someone
 > can always find more specimens and more work can always be done.)

The Neosauropoda example should clear that up.  Clades based on and
immediately branching from major branch-points are always interesting.
A few examples that spring to mind are the node-stem triplets
{Archosauria, Panaves and Pancrocodylia(*)}, {Dinosauria, Saurischia,
Ornithischia} and of course {Neosauropoda, Diplodocoidea, Macronaria}.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor    <mike@indexdata.com>    http://www.miketaylor.org.uk
)_v__/\  "There was a brief period when it looked like the midfield
         partnership of Stewart and Thomas could do something for us.
         Then again I was drinking more heavily back then." - Kev Howson.


(*) or whatever it's called.  Hopefully the PhyloCode companion volume
will sort this out.