Paraphyly and names

SKÁLA Zdenek skala at INCOMA.CZ
Mon Jan 21 13:34:09 CST 2002

From: Thomas DiBenedetto:
>Thus the amnion is an apomorphy of Amniota - discovery of the apomorphy
>evidence of the divergence of the lineage - i.e. it is good and useful
Zdenek Skala:
>> while there is a straightforward logic why synapomorphies are
>>crucial for constructing cladogram, there exists no logical reason why
>>they should be *exclusively* used for splitting the cladogram into

Thomas DiBenedetto:
>Oh yes there is. The reason is that synapomorphy (evolutionary
>recognized at their true level of generality) is the only
>that offers evidence for historical groups.

Tom, your arguments are circular. You are saying that holophyletic taxa
(including *by definition* only clades and based solely on
synapomorphies) are best *because* they are based on
clades/synapomorphies (see above: "...evidence of the divergence=good
data"). However, I perhaps understand the assumption underlying your
position and will try to rephrase; please correct me if I am wrong.
For you, I believe, the taxa (or better system) should contain
information on the phylogenetic divergence pattern. Then, holophyletic
taxa and exlusive use of synapomorphies gives perfect sense and you are
really on the best way.
However, I would like to recall that taxonomy/system (at least in its
original and most widespread meaning) is intended to summarize
information on the existing organisms' diversity (i.e. character
diversity) in a natural way. The "natural way" of course currently means
phylogeny; however I doubt that we can simply re-define taxonomy as
phylogeny reconstruction and leave the character-information aspect.
Perhaps the ways of systematics (in the original sense) and
phylogenetics now diverge; anyway this distinction is behind the
disagreement in the current thread. 
(It does not mean that holophyletic taxa have no character-information
value; they only are not *optimized* in this way.)
skala at

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