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RE: Taxa nomy?



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
> > > Forgive me for the amateur question, but if species were abandoned how
> > > would a new organism be labelled?
>
> As a clade.
>
> > So for example, to the extent that there are no known monophyletic
> > subdivisions of the specimens we know as Microraptor gui, we
> can call this
> assemblage
> > the LITU microraptor (or whatever). If they were ever discovered to form
> > monophyletic subgroups, "microraptor" is shifted to a capitalized
> "Microraptor", and
> > the smaller subdivisions get new, lower-case LITU names.
>
> *M. gui* and *M. zhaoianus* do seem to be monophyletic.

As a group? Yes.  As distinct taxa: that hasn't been demonstrated (and
personally I wouldn't put too much support in the idea that they are
distinct...).

> They are therefore
> good candidates for LITUs -- the difference to species is that the names
> would have be defined as clade names, and that we wouldn't have to worry
> about the 25 or so species concepts. :-)

Incidentally, very few researchers have adopted the LITU concept so far.
(Granted, it is only a few years old).  So I don't want folks to get the
idea that all phylogenetic taxonomists use LITUs, any more than all cladists
use phylogenetic taxonomy.

Incidentally, the LITU concepts fails is the same way that most other
species concepts (most especially the Biological Species Concept, which is
the one everyone learns in biology classes): the things we call "species" or
"LITUs" are horizontal segments of a continuous vertical sequence (with Time
being the vertical axis), rather than fixed points.  Also, the ability to
breed with your relatives is a plesiomorphic trait, so unless you evolve
attributes to prevent this, you still can.  Consequently, many taxa that
everyone would regard as distinct (morphologically, behaviorally, etc.):
lions and leopards and tigers; brown bears and polar bears; _Pseudorca_ and
_Tursiops_; _Amblyrhynchus_ and _Conolophus_, can all interbreed and produce
viable, fertile (in at least the first three cases!) offspring.
Furthermore, perfectly reasonable species by pretty much every criterion
(like _Branta canadensis_) can produce multiple distinct descendant lineages
(like the Hawaiian goose radiation, including the oviraptorosaur mimic).

This is, largely, the reason that the PhyloCode workers regard "species" and
"clades" (complete vertical branches of the Tree of Life) as distinct
things.  If there will be two alternative mutually compatible systems of
taxonomy in the future, my suspicion is that it will be a species system and
a clade system, not a cladistIC system and a Linnean heiarchy one.

My $0.02.  Off to the Proterozoic...

P.S.  Chris B.  Please come back!!!  We need you!!!

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796