Message 2001-06-0123: Re: Crown groups (long)

Sun, 17 Jun 2001 20:44:38 -0500

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Date: Sun, 17 Jun 2001 20:44:38 -0500
From: kritosaurus <>
To: David Marjanovic <>, PhyloCode mailing list <>,
Subject: Re: Crown groups (long)

A few points from the Marjanovic/ Headden conversation I thought I'd try to

1) The idea of a crown clade is the clade stemming from the most recent
common ancestor of all living forms of a particular recognized group. There
are multiple ways to define one, including picking representative species
(note that the code DOES recommend specific specifiers, as opposed to
"higher" taxa). The sentence used above has not (to my knowledge) ever been
seriously used as a definition. Instead, as has been pointed out,
conventional node-based definitions are most commonly used (although other
schema have been proposed).

2) To my knowledge, no one interested in Phylogenetic Nomenclature has
seriously accepted a phylogenetic definition which could, within the general
context in which we approach PN, result in a para- or polyphyletic group,
apart from cases in which the result is actually a contradictory definition
which is effectively meaningless (see Article 11.9, example 3)... in the
past, I have pointed out to this group that improper wording of stem-based
definitions may result in paraphyly). PN begins and ends with the naming of
clades (and, for some of us, species).

3) Mike Keesey is a nice fella, but his website is not, in my opinion, a
PhyloCode resource. Mike appears to be trying to generate a useable system
for his own use. Whether his systematics conform to those published in the
literature or not is a matter to be investigated BEFORE his material is used
as a point of argumentation. I know Mike, I like Mike, but Mike has his own
ideas on Phylogenetic Nomenclature, ones which sometimes do not reflect the
mainstream. He may have some examples worth discussing, but there are some
departures from published work, and it may be difficult for nonspecialists
to separate Mike's ideas from those which are published.

4) Use of multiple internal specifiers in a stem-based definition *is*
explicitly discussed in the (draft) Code, under Article 11.9 example 3. This
was not only Mike's idea.

5) The draft PhyloCode does include a glossary. It does not include specific
instructions for how to convert established names to PN, other than for a
scattering of technical points. At least one author, Paul Sereno, has
proffered a "rationale" for such usage, based on ideas he appears to believe
would allow straightforward, rational conversion to a new system. I am not
sure I agree, and I am working on a paper with suggestions (rather than
"rules") on the matter. I think that suggestions are really all we'll ever
have. Individual disciplines may be forced to find the conventions which
serve them best. I know that, among ornithischian dinosaurs at least, no one
"rationale" will produce a satisfactory nomenclatural scheme.

6) The draft PhyloCode suggests normal parentheses for shorthand
definitions. I suggested curly brackets on another venue many years ago, to
distinguish this shorthand from content-based notations such as Newick.
However, I have not felt this to be worth the effort of attempting to amend
the draft Code, especially since use of regular parentheses appears to be
very common anymore.


Jonathan R. Wagner
9617 Great Hills Trail #1414
Austin, TX 78759

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