[Taxacom] Paraphyletic species and paraphyletic higher taxa

[Kenneth Kinman]

Hi Curtis,
        That can often be a difficult question to answer.  Where is the
best place to draw that line, which is another way of asking which
synapomorphy or synapomorphies should define the exgroup (or
autophyletic taxon as Richard Zander prefers to call such groups).  
         Given the limited morphological information available from
fossil taxa (even more limited for molecular information), it can be
frustrating trying to narrow down the best place to make the cut.  We
might make a cut based on one synapomorphy and then later find fossils
which show a slightly earlier or later developing synapomorphy is better
for some reason.        
       However, this difficulty should not deter us from exploring and
debating such cuts, not only to better define the exgroup clades, but
also to focus our attention on these most important transitions in the
history of life.  Such transitions are where paraphyly is most
informative and useful.  It's difficult and debatable, but it is still
worth concentrating our efforts on such transitions.  Such efforts have
helped focus our attention in particular on filling the fossil gaps
between sarcopterygian fishes and early amphibians, as well as the
dinosaur-bird transition.  And if it makes classifications more stable
and useful in the long run, all the better.          Perhaps more
importantly, I would rather such cuts be made by open-ended scientific
debates that narrow down to the best choices as new evidence is
discovered and reaching a consensus (subject to minor changes by
consensus when new evidence is uncovered).  That's FAR better than
making cuts arbitrarily by some committee of PhyloCoders legalistically
proclaiming arbitrary cuts based on their authoritarian specifiers.
PhyloCode pays a tiny bit of lip-service to possibly defining some
clades with synapomorphies, but almost all of their proposed definitions
are based on certain included species (specifiers) setting the limits,
not on synapomorphies.  Those cuts are FAR MORE arbitrary than anything
I am talking about.  PhyloCode in particular takes authoritarianisn to a
whole new level.  
          --------Ken                              
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Curtis Clark wrote:   
        But where, exactly, do you draw the line? Because every
paraphyletic group precludes the existence of many others, that's where
it's argument by authority. Clades can be nested, and every synapomorphy
can diagnose a named clade, but one has to choose one paraphyletic group
over others with slightly larger or smaller excluded clades.