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Re: PhyloCode: Senter, 2005 and the definition of _Aves_



On 1/18/06, David Marjanovic <david.marjanovic@gmx.at> wrote:
> T. Michael Keesey wrote:
>
> > Furthermore, Charig's definition doesn't tie the character to a
> > particular specimen or species, so it seems to me that the form is
> > invalid, anyway.
>
> Of course.
>
> > Would PhyloCode accept Charig's definition even if it
> > did cover unregistered taxa published before its starting date?
>
> I can't imagine it.

Actually, now that I consider it again, it seems to me that it *will
be* possible to define a clade under PhyloCode without reference to
species or specimens. The draft PhyloCode only *recommends* using
node-, stem-, and apomorphy-based definitions, but allows that other
forms are possible (Note 9.4.1: "this list is not exhaustive"). I had
thought there was a provision stating that all definitions must
contain at least one internal species or specimen specifier, but I
can't seem to find it.

Charig's definition is essentially of the form, "The final common
ancestor(s) of all organisms to possess character M, plus all
descendants thereof." It's a node-based definition, but the internal
specifiers are not species or specimens but the set of organisms which
possess a character (M). You might call it a "character-specified
node-based definition." Thus it seems to me that _Aves_ sensu Charig
1985 and _Avifilopluma_ Gauthier and de Queiroz 2001 (an
apomorphy-based definition) are heterodefinitional synonyms (at least
unless we find some group of organisms that has convergently evolved
feathers [_Longisquama_? just kidding!], in which case _Aves_ sensu
Charig 1985 becomes more inclusive).

Not a very stable way to frame a definition, but it seems technically
valid, on second thought.
--
Mike Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com