[Previous by date - Re: interesting style of definition]
[Next by date - Ostrom Vol ms]
[Previous by subject - RE: crown clade convention]
[Next by subject - RE: interesting style of definition]
Date: Fri, 15 Feb 2002 11:34:31 -0600
From: "Bryant, Harold MAH" <HBryant@mah.gov.sk.ca>
To: Mieczyslaw Wolsan <wolsan@twarda.pan.pl>, PhyloCode@ouvaxa.cats.ohiou.edu
Subject: RE: interesting style of definition
Issues concerning the potential ambiguity of the meaning of the terms "stemming" and "ancestor" can be avoided by the following wording: "The least inclusive clade that includes A and all extant organisms that are more closely related to A than to B." I have not been a fan of the use of "extant" in phylogenetic definitions because of the potential effect (no matter how slight) of future extinction on the clade referred to by the definition. Jonathan Wagner's recent suggestion is one solution to that problem that could be useful in stem-modified node-based definitions. However, if one wants the definition to always refer to a crown clade, then one would want to give priority to stability in that aspect of the definition, and if later extinction changes the inclusiveness of the clade so be it. Harold ---------------------------------------------------------------------------- ------------------------------------------------ Harold Bryant Royal Saskatchewan Museum 2340 Albert Street Regina, Saskatchewan S4P 3V7 Canada 306-787-2826 FAX 306-787-2645 -----Original Message----- From: Mieczyslaw Wolsan [mailto:wolsan@twarda.pan.pl] Sent: Friday, February 15, 2002 5:11 AM To: PhyloCode@ouvaxa.cats.ohiou.edu; phyloadvisors@ouvaxa.cats.ohiou.edu Subject: Re: interesting style of definition Sorry, there was a problem with my previous posting. Now it's ok (I hope). 1) "extant" This problem has already been addressed comprehensively in the literature (see, e.g., Bryant 1996, Syst. Biol. 45: 174-189). 2) "stemming" If clade A stems from B, is it necessary for clade A to contain B? I feel it is not. And this is my point. Of course, a clade consists of an ancestor and all its descendants. The problem I find with the discussed definition is that it is not clear (for me) whether the specified "last common ancestor" is contained in the clade. If I correctly recognize the meaning of the word "stemming" , the phrasing "clade A stemming from B" referes to two different clades: one containing B, and the other without B. 3) "ancestor" There has been much discussion related to the problem, also on the list (recently by Kevin de Queiroz, as far as I remember). The draft PhyloCode defines the term "clade" as "a group of species comprising a common ancestor and all of its descendants". (I would say "a group of lineages" and would replace the word "comprising" by "composed of" because I feel the word "comprise" meant to contain or include, but not to constitute or to compose.) I think that the majority of systematists agree with the draft PhyloCode's definition. However, I do not think that according to this definition it is necessary for the ancestor to be a species. I think many systematists agree that it is not necessary for a clade to begin with a complete species. If one wishes to have a species as an ancestor, this should be explicitly stated in the definition. Mieczyslaw 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