You wrote:

Morphological data aren't the only valid data, though. Evidence of genetic disparity is, these days, generally considered to be of greater importance and utility in taxonomy, though only the hardcore cladists (Burbrink comes to mind) are willing to use it to split a taxon into morphologically indistinguishable taxa.



My response:

Molecular data of all sorts have indeed proven more useful than morphological similarities in elucidating branching order. However, it is cladistic dogma to ignore morphological disparity in classification, since Hennig rejects its use. The way Burbrink split Elaphe guttata is no different than the way Utiger et al. have splintered Elaphe; they both ignore morphological disparity and only rely on branching order only.



You wrote:

I'd guess that Utiger et al. don't explicitly mention morphology for some of their taxa simply because the morphological disparity among the members of Elaphe sensu lato is so conspicuous and has been previously reported often enough that they figure their readers are already well aware of it.



My response:

My interpretation is different. As one can see by the two new genera they coin, there isn't any good morphological character to distinguish one genus from another since these characters are variable intragenerically or even intraspecifically. On the other hand, the taxa they recognize clearly are delimited from their consensus cladogram. Each major branch in that cladogram is classified as a different genus. That is no different than Burbrink, who classifies each major branch in his analysis as a different species.



You wrote:

And that question is simply a judgment call--they could provide all the data on morphological disparity they wanted, and still have no objective means of demonstrating that the disparity is `enough'. I think most people familiar with Elaphe sensu lato will agree, though, that the disparity is indeed enough for generic distinction to be appropriate



My response:

It is true that there is no objective measure of morphological disparity. Darwinian taxa are indeed subjectively delimited. The alternative is far worse. The cladists, who have no guideline for delimiting taxa other than equal rank for sister taxa, are far more subjective. Kluge, for example, states that he can either recognize one, two or three genera given the particular topology of his cladogram. He finally decides that, for the sake of taxonomic efficiency, he will recognize but one genus for Charina bottae, Lichanura trivirgata and Calabaria reinhardtii. I submit that taxonomic efficiency is not an objective method for classifying organisms. In fact, it is far more subjective than if one relies on morphological disparity. Below I have two trees with very similar topologies to illustrate my point. The top one is from Kluge's study of erycine relationships. The bottom one is a hominoid tree that is accepted by most scientists. If one totally ignores morphological disparity, then a cladist may choose either one, two or three genera to classify the bottom set of taxa. The first alternative of lumping all three into the same genus results in a morphologically heterogeneous taxon. The second alternative is to recognize three genera, meaning that Pan paniscus and Pan troglodytes would be classified in different genera, not very satisfactory. The third alternative is to recognize Pan and Homo as valid genera, the nearly universally accepted classification. Without any guidelines, the cladist is free to choose among any of these three equally valid alternatives. The Darwinians, however, are far more likely than not to choose the third alternative of recognizing 2 genera since they take morphological disparity into account.



Finally, as Kluge demonstrates, it is equally valid for the cladist to lump all taxa sharing a single ancestor into one genus as it is to recognize each terminal node as a different genus. Hence Utiger et al. do not have to splinter Elaphe. They can lump all species of Elaphe into a single genus. Doing so, however, would mean that they would have to transfer all species in the Lampropeltini back into Elaphe. Neither alternative is satisfactory since the taxa that result are too heterogeneous. The best alternative unfortunately, is one that is not available to the Hennigians, who are intolerant of paraphyletic taxa. The Darwinians, since they have no ideological aversion to paraphyly, can maintain the status quo and recognize a paraphyletic Elaphe and all of the genera currently assigned to the species within the Lampropeltini, which include Pituophis, Lampropeltis, Arizona, Cemophora and Stilosoma.

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