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Date: Thu, 23 Aug 2001 16:05:04 +0200
From: David Marjanovic <david.marjanovic@gmx.at>
To: PhyloCode mailing list <phylocode@ouvaxa.cats.ohiou.edu>
Cc: Mike Taylor <mike@tecc.co.uk>
Subject: Apomorphy-based definitions
I tried to help Dinosaur mailing list member Mike Taylor with his explanation of cladistics at http://www.miketaylor.org.uk/dino/faq/s-class/phyletic/index.html. The following came back: ----- Original Message ----- From: "Mike Taylor" <mike@tecc.co.uk> To: <david.marjanovic@gmx.at> Cc: <dinofaq@yahoogroups.com> Sent: Thursday, August 23, 2001 10:43 AM Subject: Re: [dinofaq] "What do terms like monophyletic" etc. "mean?" > > Date: Thu, 23 Aug 2001 10:06:10 +0200 > > From: "David Marjanovic" <david.marjanovic@gmx.at> > > > > >> Clade(X in A) is an apomorphy-based definition meaning ``the first > > species to possess character [X] synapomorphic with that in A, together with > > all its decendants.'' > > > > Whatever the hell that means.<< > > > [...] > > > - Suppose you'd be naive enough do define birds as possessing > > feathers. 8-) Then the definition would read "the first species that > > possessed feathers synapomorphic with those of *Passer*, and all its > > descendants" and be abbreviated as (Feathers in *Passer*). > > I guess I sort of knew that really, I just couldn't resist the > side-swipe at apomorphy-based definitions, which seem like a bit of a > stupid thing to me, since you can't really say _anything_ useful about > their membership. > > But what does "synapomorphic with those of *Passer*" mean in this > context? Isn't it circular? How can you decide whether the feathers > are synapomorphic? > > > PhyloCode recommends such definitions for character-based names such > > as Macronaria or Pygostylia. > > I'm amazed the PhyloCode allows this behaviour at all. Coming to think of it, apomorphy-based definitions _are_ circular, aren't they? Are any apomorphy-based definitions in use?