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Date: Tue, 26 Feb 2002 18:45:22 -0600 (CST)
From: jonathan.r.wagner@mail.utexas.edu
To: "T. Mike Keesey" <tmk@dinosauricon.com>
Cc: "Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu>, -PhyloCode Mailing List- <PhyloCode@ouvaxa.cats.ohiou.edu>
Subject: Re: Crown clade definitions (was: Re: interesting style of definition)
Quoting "T. Mike Keesey" <tmk@dinosauricon.com>:
> I guess what bugs me is that in this case content could change based on
> something OTHER than a new understanding of topology. (Although I suppose
> the same could hold true for apomorphy-based definitions....)
Well, the content of ANY phylogenetic taxon can change based on changes
other than new interpretations of topology. In fact, there is one way in which
the interpreted content of a clade named by any type of definition can change
in the same manner as you described for explicit crown-clade definitions:
discovery of a new taxon. Discovery of a new member of a clade always increases
the interpreted content by one member.
Now, this will sometimes change the *ancestor* of the clade, which is a
point worth examining. Discovery of a previously unrecovered, extant form
outside the currently known clade of extant forms *does* associate the name
with a new ancestor (assuming an explicit crown-based definition). However, we
can rationalize this by stating that our error lay in associating the name with
the wrong ancestor.
Wagner