Message 2002-02-0009: Re: interesting style of definition

Fri, 15 Feb 2002 10:38:55 -0500

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Date: Fri, 15 Feb 2002 10:38:55 -0500
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
Subject: Re: interesting style of definition

I just wanted to point out that this is not a new style of definition but =
one (called a "stem-modified node-based definition") that has been =
described and discussed in the literature.  It is not particularly similar =
to an apomorphy-based definition but instead uses components of both =
standard node- and stem-based definitions (as implied by the name).  See =
Wyss and Meng 1996 Systematic Biology 45:559-568.

Kevin de Queiroz

>>> "T. Mike Keesey" <> 02/13/02 16:57 PM >>>
I've just received _New Perspectives on the Origin and Early Evolution of
Birds: Proceedings of the International Symposium in Honor of John H.
Ostrom_. The first chapter, "Feathered dinosaurs, flying dinosaurs, crown
dinosaurs, and the name 'Aves'" by Gauthier and de Queiroz, should be of
interest to anyone concerned with PhyloCode. It's written according to the
draft PhyloCode rules and recommendations (i.e., italicized clade names,
very specific and detailed definitions, etc.)

There's a big emphasis, it seems, on using apomorphy-based clades and
crown clades. Also, every stem-based clade mentioned has the prefix
"Pan-" (_Panaves_, _Panpaleognathae_, _Panneognathae_, etc. -- all new
clade names).

One of the more interesting styles of definition used therein runs like
"the crown clade stemming from the last common ancestor of A and all
other extant organisms sharing a more recent ancestor with A than with B."
(In essence, using the extant members of a stem-based clade as specifiers
for a node-based clade.)

This doesn't seem to me to be allowed under the draft PhyloCode, which
"11.3. When a species is used as a specifier, the author and publication
year of the species name must be cited"

Only one of the specifiers (A) is being cited with author and publication
year. (B is not a specifier of the clade in question.) The rest are
identified by a formula, not by citation.

Any thoughts on this style of definition? Should the final PhyloCode allow
identification of specifiers through formulae, and not just direct
citation? It seems useful to me (although potentially destabilizing if we
find some extant member outside what had formerly been the crown group).

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