CKing:
You claim that "species and or clades with distinctive apomorphies" are "natural objects." You also claim that species can be paraphyletic. Then you claim that paraphyletic taxa are "imaginary." How can a species, which is both paraphyletic and natural, be imaginary?

Me:
Species CAN be paraphyletic because bits of them can bud off as new species which are then more closely related to some members than others in the 'parent' species. BUT THEY GET OVER IT - because of reproductive continuity, a species can re-establish monophyly over time (as all individuals living at some later time will share common ancestry since the last speciation). Species are the most inclusive groups that can be 'ancestral to themselves' in this way (under the BSC). And THAT's why rules for naming species have to be different from those for naming higher taxa. Paraphyly in species is a passing phase; paraphyly in higher taxa is irremediable except by the taxonomic action of re-including the other descendants of the common ancestor. Paraphyletic higher taxa are unnatural because, in reality, those other descendants NEVER LEFT THE LINEAGE.

CKing:
I agree with you that taxonomy is important for communication both among scientists and between scientists and the general public. A term such as reptile is universally understood among both scientists and the general public. By redefining reptiles to include birds, some taxonomists have made communication more difficult. Further, since mammals are also descended from a reptile, the exclusion of the mammals from the Reptilia creates a paraphyletic basal group of primitive amniotes, which were once considered reptiles but is not a paraphyletic group without a name. This paraphyletic group is still part of Amniota, but it now has no name, making it impossible for scientists who adhere to this sort of cladistic absurdity to communicate with each other. This is madness, not progress.

If clades are natural, how come we can no longer classify some groups (such as the paraphyletic basal amniotes) if we recognize other groups such as mammals and Gauthier's "Reptilia"?

Me:
The clade called Reptilia is a useful thing to name because it is a natural object in the world. I notice you seem to have no trouble with the concept of Amniota, which is equally natural and also does NOT correspond to a unitary 'concept' in the languages used by the biologically naive or otherwise pre-cladistic general public (people like Romer whose concept of 'reptiles' might be restated as: amniotes that aren't mammals or birds; as well as those who group reptiles and amphibians as a single concept like Linnaeus' 'Amphibia'). If the problem is that Reptilia (unlike Amniota) has the same name as a traditional paraphyletic concept, that is something that can be clarified in a moment if somebody gets confused in the course of discussion. (Two different words can have the same origin and spelling, that's just one of the ways language evolves, like gene duplication.)

Cladists recognising a monophyletic Reptilia DOES NOT create a paraphyletic group of basal amniotes; that's what people like your heroes do. Organisms that are are amniotes but not reptiles or mammals form a paraphyletic assemblage that doesn't deserve a collective name in formal taxonomy, although we can easily refer to them collectively - as I just did. Of course they're all extinct, so the details of their biology are the province of specialists who can give an explicit list of the monophyletic or species-level taxa they are discussing rather than trying to adapt a folk taxonomy that just doesn't apply. Your objection is refuted.
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John D. Scanlon
Riversleigh Fossil Centre
Outback at Isa
Mount Isa, Queensland, Australia

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