Message 2004-02-0002: Re: a comment on ancestors

Wed, 04 Feb 2004 12:34:29 +0100

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Date: Wed, 04 Feb 2004 12:34:29 +0100
From: David Marjanovic <>
To: PML <>
Subject: Re: a comment on ancestors

> If you define a taxon by a character or by a type you mean that it
> is possible to allocate any newly discovered item to that taxon
> by observing respective character or type.

This would not guarantee that the taxon would stay monophyletic -- the
character in question could have evolved by convergence.

> The present PhyloCode definition of taxon membership
> presumes that in order to allocate a new item to one or
> another monophyletic group in existing classification, one
> has to run complete cladistic analysis in which all members
> of those groups + new item are to be included.

Correct. Well, not necessarily all members, but some that are universally
agreed to be members of that group (such as the specifiers).

> But what to do if those groups were recognized, say, by
> DNA analysis and no DNA data are vailable for the new item?

:-) Make a morphological analysis for them.
        This wouldn't change under an apomorphy-based definition. If
Afrotheria were defined by their unique 9 bp deletion in the gene BRCA1, and
if I wanted to find out if some Paleocene fossil was an afrothere, I'd
likewise have to make a morphological analysis of Placentalia.

> It seems to me that theoretical and empirical definitions of taxon
> membership are mixed in the PhyloCode.

I disagree. The theoretical definition is called "definition" in it, while
the empirical definition is called "diagnosis".


Feedback to <> is welcome!