Message 2001-02-0011: Re: apomorphy-based names

Tue, 06 Feb 2001 10:42:16 -0500

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Date: Tue, 06 Feb 2001 10:42:16 -0500
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
Subject: Re: apomorphy-based names

David Baum wrote:
"at the same time, I remain unconvinced that, as Kevin put it, "....
sometimes an apomorphy-based definition is the appropriate definition for
the clade concept being named."  A good synapomorphy certainly can provide
good evidence that one has identified a clade, and can be immensely useful
when communicating the identity of a clade to somebody.  However, I cannot
see why it would ever be the appropriate DEFINITION of a clade concept.
What is to stop you aiming for a stem-based or node based definition, even
a conservative one listing lots of specifiers?"

When one examines the way in which certain names are used, it becomes very =
clear that some people have an apomorphy-based concept of the clade to =
which they are referring.  For example, some authors clearly wish to name =
the clade stemming from the first vetebrate species to evolve feathers =
rather than either the clade of Passer domesticus and everything sharing a =
more recent common ancestor with it than with Deinonychus antirrhopus, or =
the clade stemming from the most recent common ancestor of Passer =
domesticus and Archaeopteryx lighographica. =20

"Systematists are very good at not reading too much into the literal =
meaning of names."

Although there is some truth to this statement, the situation is not =
nearly as simple as David suggests.  That is, sometimes they're good at =
it, and other times they are very bad at it.  In addition, names are =
generally most easily remembered (which makes them more useful) when used =
in a way that is consistent with their etymology.

"I hope that one day the vertebrate paeontological types, and whoever else =
is inclined towards apomorphy-based definitions, can be convinced to =
make-do with stem-based and node-based definitions."

It probably isn't a coincidence that paleontologists may want to name =
apomorphy-based clade concepts more often than do neontologists.  After =
all, paleontologists often (though not always) have to make finer =
distinctions than neontologists.  Thus, for neontologists, all of the =
clades that I described above (i.e., clade from first featered vert; clade =
P. domesticus <-- D. antirrhopus; and clade A. lithographica + P. =
domesticus) all have precisely the same composition (i.e., considering =
only extant organisms).  But for paleontologists, the composition of these =
taxa differs, and thus additional names, which neontologists can do =
without, are often useful for them.  Although it might be argued that =
paleontologists could name intermediate nodes or stems instead, it is =
sometimes clear that these are not the clades tht they really want to =
name.  To my way of thinking, one of the great strengths of phylogenetic =
nomenclature is that it permits systematists to name the clades that they =
really want to name.  If we restrict this freedom, our system becomes more =
arbitrary and artificial, and in these respects, more like the traditional =
system. =20

"P.S.  I think "node-based," "stem-based," and "apomorphy-based" should be
in the PhyloCode glossary"

I agree.


Kevin de Queiroz
Division of Amphibians & Reptiles
National Museum of Natural History
Smithsonian Institution
Washington, DC  20560-0162
Phone:  (202) 357-2212
FAX:  (202) 786-2979


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