Message 2002-02-0002: Re: interesting style of definition

Thu, 14 Feb 2002 11:23:23 +0100

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Date: Thu, 14 Feb 2002 11:23:23 +0100
From: Michel Laurin <>
Subject: Re: interesting style of definition

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 formulae that they have reportedly used.  It is a 
convenient way of insuring that we define a crown-group, even when 
the phylogeny of that group is poorly understood.  And of course, it 
would be unreasonable to ask the author to cite the papers in which 
all the species indirectly alluded to in such a formula were erected.



>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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Michel Laurin
Equipe 'Formations squelettiques'
CNRS - UMR 8570
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