Conodont assemblages from the Bashkirian-Moscovian boundary interval in the Naqing section, South China have been studied in detail. A landmark-based geometric morphometric analysis of the evolution of Diplognathodus ellesmerensis is presented. This analysis helps demonstrate that a distinct new species, D. benderi sp. nov., is the direct evolutionary ancestor of D. ellesmerensis. The potential of using the first appearance datum (FAD) of D. ellesmerensis as the Bashkirian-Moscovian boundary marker is re-evaluated via biostratigraphic correlations of conodonts and other fossil groups between different palaeogeographical basins. The FAD of D. ellesmerensis from within the D. benderi sp. nov.-D. ellesmerensis lineage is an excellent potential marker to recognize a global Bashkirian-Moscovian boundary because of its global distribution, the abundance of supplementary marker species at similar stratigraphical levels, and the close stratigraphic proximity of the FAD to the traditional Bashkirian-Moscovian boundary, thus largely preserving the original concept of the base of the Moscovian Stage.