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Date: Thu, 14 Feb 2002 15:37:56 +0100
From: Mieczyslaw Wolsan <wolsan@twarda.pan.pl>
To: PhyloCode@ouvaxa.cats.ohiou.edu, phyloadvisors@ouvaxa.cats.ohiou.edu
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= =20 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= =20 speaker I cannot evaluate this properly, but I do not think that the word=20 "stemming" specifies this unambiguously). Third, "the last common ancestor"= =20 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= =20 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. Mieczyslaw 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= =20 > 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 >>so: >>"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 >>states: >>"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). >> >>__________________________________________________________________________= ___ >>T. MICHAEL KEESEY >> The Dinosauricon <http://dinosauricon.com> >> BloodySteak <http://www.bloodysteak.com> >> personal <keesey@bigfoot.com> -->= <tmk@dinosauricon.com> >> Dinosauricon-related <dinosaur@dinosauricon.com> >> AOL Instant Messenger <Ric Blayze> >> ICQ <77314901> >> Yahoo! Messenger <Mighty Odinn> > > >-- >********************************** >Michel Laurin >Equipe 'Formations squelettiques' >CNRS - UMR 8570 >Case 7077 >Universit=E9 Paris 7 - Denis Diderot >2, place Jussieu >75251 Paris cedex 05 >France >Tel. (33) 1 44 27 36 92 >Fax. (33) 1 44 27 56 53 >http://phylogeny.arizona.edu/tree/laurin/Laurin_Home_page.html >********************************** 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 E-mail: wolsan@twarda.pan.pl http://www.paleo.pan.pl