Message 2002-02-0003: Re: interesting style of definition

Thu, 14 Feb 2002 15:37:56 +0100

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Date: Thu, 14 Feb 2002 15:37:56 +0100
From: Mieczyslaw Wolsan <>
Subject: Re: interesting style of definition

There are at least three problems with this definition. First, the clade=20
referred to by the definition changes with the extinction of taxa; and this=
is the most serious problem. Second, it is not clear whether "the last=20
common ancestor" is contained in the clade or not (as a non-native English=
speaker I cannot evaluate this properly, but I do not think that the word=20
"stemming" specifies this unambiguously). Third, "the last common ancestor"=
may refer to either a species or a population, or a breeding pair,=20
individual organism, etc.; in each instance, we have to do with a different=
clade. This might seem like extreme pedantry, but if explicitness in=20
phylogenetic nomenclature is important, this should be reflected in the=20
wording of phylogenetic definitions.


At 11:23 14-02-2002 +0100, you wrote:
>Dear fellow phylocoders,
>         I have not seen the chapter by Gauthier and de Queiroz alluded to=
> by Mike, but I think that we should allow the type of definition by=20
> formulae that they have reportedly used.  It is a convenient way of=20
> insuring that we define a crown-group, even when the phylogeny of that=20
> group is poorly understood.  And of course, it would be unreasonable to=20
> ask the author to cite the papers in which all the species indirectly=20
> alluded to in such a formula were erected.
>         Sincerely,
>         Michel
>>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).
>>  The Dinosauricon        <>
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>Michel Laurin
>Equipe 'Formations squelettiques'
>CNRS - UMR 8570
>Case 7077
>Universit=E9 Paris 7 - Denis Diderot
>2, place Jussieu
>75251 Paris cedex 05
>Tel. (33) 1 44 27 36 92
>Fax. (33) 1 44 27 56 53

Mieczyslaw Wolsan
Professor and Chair
Department of Vertebrate Paleontology
Institute of Paleobiology
Polish Academy of Sciences
Twarda 51/55
00-818 Warszawa, Poland
Phone: +48-22-697-8793
Fax: +48-22-620-6225


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