This subject has been discussed ad nauseum in the threads below and in the older threads of this forum. Nevertheless, Pantherophis is a genus that is proposed not because it is morphologically disparate from Elaphe, and not because it does not share a common ancestor with Elaphe, but because some systematists have the misguided belief that paraphyletic taxa are not acceptable.

As R. F. Carroll (1988:11-13) pointed out:

"Hennig coined the term PARAPHYLETIC for groups that have a common ancestry, but from which one or more descendant groups have been excluded. Cladists in general discourage the recognition of paraphyletic groups..., the existence of paraphyletic groups is an inevitable result of the process of evolution."

To briefly summarize, to recognize Pantherophis is to ignore the fact that evolution produces paraphyletic groups such as Elaphe. Elaphe is paraphyletic because some of its descendant groups, e.g. Pituophis, Lampropeltis, Arizona and Bogertophis, have not been included in the genus Elaphe by past systematists because of morphological disparity. Some systematists that adhere to cladistic ideology have therefore sought to eliminate paraphyly by redefining Elaphe as a much smaller genus, and by resurrecting long forgotten names (like Pantherophis) or erecting names to accomodate the remaining fragments of their wholesale destruction of the paraphyletic taxon Elaphe. People who do not adhere to cladistic ideology therefore have no compelling reason to recognize Pantherophis.

As for the status of the population known as emoryi, some cladists have also proposed that it be recognized as a species on the basis that it is a lineage. But species are not lineages. Species are a set of actually or potentially interbreeding populations. mtDNA data has shown that emoryi shares a common ancesor with the eastern subspecies of Elaphe guttata, and that it is in fact ancestral to the eastern subspecies. Reproductive isolation has not been demonstrated between emoryi and E. g. guttata. Therefore no compelling evidence for the recognition of emoryi as a full species has been proffered.

Reference

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

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