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Date: Tue, 06 Feb 2001 10:42:16 -0500
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
To: PhyloCode@ouvaxa.cats.ohiou.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 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 e-mail: dequeirk@nmnh.si.edu