Message 2001-09-0006: Re: Apomorphy-based definitions

Fri, 24 Aug 2001 11:20:42 -0400

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Date: Fri, 24 Aug 2001 11:20:42 -0400
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
Subject: Re: Apomorphy-based definitions

I think you are misconstruing function of the specifier Passer in the =
definition, which is not to define the what is meant by "feathers" but to =
protect the definition against homoplasy.  Thus, saying that the feathers =
are synapomorphic with those in Passer does not mean that they must be =
more similar to those in Passer than to those in ratites.  It only means =
that whatever features we consider necessary to call something a feather =
(presumably shared by Passer and ratities) must be shared with Passer as =
the result of inheritance from a common ancestor for the organism to be =
considered to fit the definition.  The only way that ratities would be =
excluded is if they evolved their feathers homoplastically with those in =
Passer.  Note that the PhyloCode (Rec. 9F) recommends that if an apomorphy-=
based definition is used, the apomorphy needs to be described in sufficient=
 detail that users of the definition can understand the author's intent.  =
Therefore, you wouldn't just say "feathers homologous with those in =
Passer"; you would also have to specify what you meant by "feathers."

>>> David Marjanovic <> - 8/23/01 5:11 PM >>>

>   This definition would be a very bad idea. For one thing, the feathers =
*Passer* are suddenly
> the defining feature for feathers as a phylogenetic tool; ratite =
are different, foir the
> bulk of their morphology, and it is conceivable that Ratitae would be
excluded from this
> definition.

Completely true; I have used this example because I have read it somewhere
(probably Sereno's rationale in Neues Jahrbuch) and for a moment thought =
was in the PhyloCode (wrong).


Feedback to <> is welcome!