Re: Apomorphy-based definitions

["David Marjanovic" <david.marjanovic@gmx.at>]

> << Drop apomorphy-based definitions... >>

BTW, the semilunate, about whose evolution we know too little, is IMHO not
an apomorphy worth of being used in a definition.

> Say a species splits into two
> isolated populations, A and B. After a while, A and B accumulate
characters
> that distinguish them (and prevent interbreeding) at the species level.
Where
> do we draw the line and say that populations A and B have become different
> species? At the split (which is where a cladist might draw the line), when
> they were still the >same< species, or afterwards, when they have acquired
> evolutionary novelties and >really are< different species?

The boundaries of clades and species need not coincide. The split you
describe is the split between 2 clades and not between 2 species, IMHO.
(Really a humble opinion -- there is still a discussion about these
nomenclatorial issues.)

> Given a fossil,
> how do you tell which taxon it belongs to? By the characters it
exhibits--not
> by trying to guess whether it falls above or below the split.

Wait a little. When we're talking about clades, we first look at its
characters. Then we use the characters to find out whether it falls above or
below some split, and then we use this hypothesis to tell which taxon it
belongs to.

> Apomorphy-based
> definitions are truer than node-based definitions.

I do think we should generally keep definitions and diagnoses separate.

Anyway, from what little traffic there is on the PhyloCode mailing list it
seems like apomorphy-based definitions are not going to be forbidden. See
Note 9.4.1 and Recommendation 9F at
http://www.ohiou.edu/phylocode/art9.html.