Message 2001-02-0025: Re: apomorphy-based names

Wed, 07 Feb 2001 16:46:03 -0500

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Date: Wed, 07 Feb 2001 16:46:03 -0500
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
Subject: Re: apomorphy-based names

In response to a previous posting from me, David Baum wrote:

"It is true that we sometime conceptualize clades based on apomorphies. =
example, like most botanists I think of Angiospermae as being "defined" by
the enclosure of ovules/seeds in carpels.  (Perhaps this reflects some =
of essentialistic core in us all that drives us to insert evidence
[characters] as proxies for things [clades] whose existence we cannot
directly observe.)  However, I think that when we get to the point of
naming a clade within the framework of the PhyloCode (or converting a
preexisting name) we should be required to go beyond a "primitive,"
character-based understanding and say something about historical
relationships.  Thus, I think the name, "Angiospermae"  should be attached
to a specific genealogically specified clade:  E.g.,"The most inclusive
clade including Arabidopsis thaliana but not Gingko biloba, Pinus
sylvestris, Welwitschia mirabilis......" or " the least inclusive clade
including Amborella trichopoda, Nyphaea, etc......)."

"Similarly, just because hair, mammary glands, a dentary-squamosal joint =
whatever (!) have been taken to "define" (I prefer "diagnose") a clade
named Mammalia does not, in my mind, negate the responsibility to attach
the name to one unambiguously indicated clade.  And the least ambiguous =
to attach names to clade is using specifiers (and even then we are =
a strictly divergent tree [but that's another topic!])."

First, apomorphy-based definitions also associate names with genealogically=
 specified clades.  But the point I was trying to make is not that any =
particular name, such as Angiospermae or Mammalia, out to be defined using =
an apomorphy-based definition.  Indeed, I would define both of these names =
as the names of crown clades using node-based definitions.  Instead, the =
point I was trying to make was that someone might want to name the clade =
stemming from the first species ancestral to Homo sapiens that evolved a =
dentary-squamosal jaw articulation, and they ought to be able to do that. =

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


Feedback to <> is welcome!