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Re: Greg Paul is right (again); or "Archie's not a birdy"

 Provided a clean dichotomy. Our analyses by necessity treat "species"
 as individuals with zero dimension in space and time. This assumption
 is usually accurate enough (at least for nonmolecular datasets), but
 there is no guarantee it is correct. And for paleontological
 datasets, it is usually not even testable.

 Besides, the neontological experience is that nodes as dichotomies
 may be more fiction than fact - not always, but often (alternatively:
 that nodes as dichotomies are arbitrary and evolutionary quite
 meaningless entities).
 http://sysbio.oxfordjournals.org/content/57/5/719.full It is unlikely
 that this is a recent phenomenon.

But, you know, a million years or three of extinction make it look like a clean dichotomy in the vast majority of cases, and 100 Ma most definitely do.

Besides, the PhyloCode has two articles that deal with reticulation and hybridogenesis. They are problems for phylogenetics, but not for nomenclature (and they aren't intractable problems for phylogenetics either).

And finally, our knowledge of "species" of Mesozoic dinosaurs usually _is_ restricted to a single individual. :-)