Has the utility of Dicynodon for Late Permian terrestrial biostratigraphy been overstated?

Abstract

Dicynodont therapsids have long played an important role in global Late Permian and Triassic biostratigraphy, including recent studies of the effects of the extinction at the Permian-Triassic boundary on terrestrial vertebrates. In particular, the last appearance of the Late Permian taxon Dicynodon has been used to mark the Permian-Triassic boundary in the Karoo Basin of South Africa and to correlate this basin with others in Africa, Europe, and Asia. These practices assume that the named taxon Dicynodon corresponds to a biologically real entity. Here we present the results of a phylogenetic analysis that suggests that this is not the case. Our analysis includes two species referred to Dicynodon that occur only in Russia and the type species that occurs in southern Africa. Our results suggest that these three species do not form a clade to the exclusion of all other dicynodonts; the alternative hypothesis of a monophyletic Dicynodon is more weakly supported. Although preliminary, our analysis challenges the use of Dicynodon for biostratigraphic correlations between Russia and South Africa, and we urge caution in using this taxon to correlate other widely separated basins. This study also emphasizes that without phylogenetic information, there is no guarantee that named taxa represent biologically real entities, and the uncritical use of named taxa can easily lead to spurious biostratigraphic correlations.