Cladistics and mass extinctions: the example of conulariids ( Scyphozoa, Cnidaria) and the End Ordovician Extinction Event

The End Ordovician Extinction Event (EOEE) had little impact on supra-specific diversity and disparity within the order Conulariida (Scyphozoa, Cnidaria). With two possible exceptions (Exoconularia and Glyptoconularia), all eight genera currently known from strata of middle or late Katian age survived the crisis, and nearly all of the discontinuous gross morphological features present in Ordovician and older genera are present in at least one of the surviving genera. A cladistic parsimony analysis of 17 genera, 12 of which occur in Ordovician strata, produced 3 major subclades and 7 less inclusive subclades within Conulariida. With one possible exception, the clade Anaconularia+Baccaconularia, all other monophyletic groups within Conulariida survived the EOEE. Moreover, additional, ghost lineages in the clade Climacoconus+Holoconularia+Notoconularia+Paraconularia+Reticulaconularia must have crossed the Ordovician-Silurian boundary. The minor impact of the EOEE on diversity and disparity within Conulariida probably reflects the eurytopic character and simple but efficient metabolism (possibly glycolysis-based) of this group.