Feldman and Parham (2002) are proposing to split the small North American turtle genus Clemmys because "The paraphyly of the genus Clemmys Ritgen 1828 requires a taxonomic revision of the nonhinged emydines."

The word "required" is dubious. There is no requirement, for example, under the rules of the ICZN to revise a taxon because it is paraphyletic. Nor does the Darwinian or evolutionary school of systematics require the revision of a taxon because it is paraphyletic. Only the Hennigians who straightjacket themselves with Hennig's arbitrary principle of holophyly are "required" by their methodology to destroy paraphyletic taxa.

In fact, R. L. Carroll (1988:13) wrote: "The existence of paraphyletic groups is an inevitable result of the process of evolution. Their existence requires that we define them in terms of the absence of the characters of their descendants as well as the presence of characters absent in their ancestors."

Hence all that a paraphyletic taxon requires is a definition. There is no requirement that paraphyletic taxa be revised, disqualified or destroyed.

Mayr and Ashlock (1991) went further than Carroll. They wrote: "Hennig developed the cladistic method on the basis of the assumption that new species originate by the splitting of a stem species into two daughter species. hence on the principle of dichotomy: The parental species disappears with the birth of the two daughter species. He saw the origin of new higher taxa in an equivalent manner as a dichotomous process. Much research of the last 50 years has indicated, however, that budding is a far more frequent way of originating new taxa than is splitting. When a new species originates by means of peripatric speciation, this has no effect on the parental species from which the neospecies has budded off. However, by Hennig's criteria, a species which has given rise to a new species by budding thereby becomes paraphyletic and has to be removed from the classification, even though it has not been affected by the budding event. The same alignment pertains to higher taxa, most of which evidently originated by the budding off of an enterprising new species that was successful in a new niche or adaptive zone. The parental taxon continued to flourish unchanged in its traditional niche, but it has become paraphyletic by cladistic definition and must be excluded from the classification. It is now fully evident that the proposal to disqualify paraphyletic groups from recognition in classifications is not only impractical and destructive but scientifically untenable."

If Hennig's classificatory philosophy is based on an erroneous assumption, then why do many systematists follow this scientifically untenable practice of destroying paraphyletic taxa?

Regardless of the reason for the disqualification of paraphyletic taxa, the result is often the splintering of a morphologically homogeneous group that is also monophyletic to most scientists who do not subscribe to Hennig's redefinition of the term monophyletic. In the case of Clemmys, Feldman and Parham are proposing to splinter the 4 species within this genus into 3 different genera: Emys, Calemys and Clemmys. Just like Utiger et al., Feldman and Parham do not even attempt to define the genera they resurrect. That is not a mystery because as Lazell (1989) pointed out, contrived genera cannot be consistently defined because the species in which these genera are placed are similar to one another and to their common ancestor because they have not changed for long periods of time. So, the cladists are replacing morphologically homogeneous paraphyletic taxa that can be defined, as Carroll pointed out, "in terms of the absence of the characters of their descendants as well as the presence of characters absent in their ancestors" with contrived taxa that cannot be consistently defined because they are not distinguishable from one another. This is scientific progress? Or is the cladists' destruction of paraphyletic taxa, as Mayr and Ashlock pointed out, scientifically untenable?

Reference

Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. W.H. Freeman and Company. New York

Feldman, C. R. and J. F. Parham 2002. Molecular Phylogenetics of Emydine Turtles: Taxonomic Revision and the Evolution of Shell Kinesis. Molecular Phylogenetics and Evolution 22(3): 388–398

Lazell, J.D., Jr. 1989. Phylogenetic systematics of iguanine lizards (Review). Copeia 1989:807-809

Mayr, Ernst and P. Ashlock 1991. Principles of Systematic Zoology, 2nd. ed. McGraw Hill

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