Revision of the Carnian/Norian conodonts through the application of cladistic analyses

The taxonomy of the Upper Carnian/Lower Norian conodont platform elements is problematic for the large number of forms occurring in this relatively short stratigraphic interval and for the high intraspecific variability affecting many species. The abundance of synonymies per species and the absence of an established phylogenetic model contributes to increase this systematic confusion. In the attempt to solve the taxonomic and phylogenetic problems of the Upper Triassic P1 conodont elements, we applied numerical cladistic analysis to the species belonging to the five most widespread genera (Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella) from the Pizzo Mondello section (Sicani Mountains, Western Sicily, Italy), GSSP candidate for the Norian (Nicora et al., 2007; Balini et al., 2008). These analyses confirmed the validity of a series of evolutionary trends among the platform elements, evidenced the most important morphological characters for their classification and allowed to make order in the systematic position of the analyzed taxa. Metapolygnathus, Epigondolella and Norigondolella resulted in fact monophyletic groups and, thus, true phylogenetic genera. Paragondolella and Carnepigondolella emerged instead to be paraphyletic grades including basal members of, respectively, the whole clade and a less inclusive group containing Metapolygnathus and Epigondonella, and thus only primitive evolutionary stages of the other three taxa and not true phylogenetic genera. These results show the potentiality of applying cladistic methods also to parataxonomic taxa. Parsimoniously grouping by synapomorphies (shared derived character states) provides in fact always a more informative and natural classification than using simple similarities (phenetics).