Geographic dynamics of some major graptolite taxa of the Diplograptina during the Late Ordovician mass extinction in South China

The study of graptolite paleobiogeography is important for understanding the relationship between geography and evolutionary dynamics in graptolites. However, there have been few detailed studies of graptolite paleobiogeography during the Late Ordovician, or the role that geography played in the Hirnantian Mass Extinction (HME). In this study, in order to investigate the geographic dynamics of major graptolite taxa during the HME, a data-set of graptolite occurrences in the late Katian-Hirnantian from 61 localities in South China was compiled using the GBDB online database. The minimum polygon method was used to reconstruct 14 distribution maps of 5 major taxa belonging to the Diplograptina. The geographic dynamics of most diplograptine taxa show a small reduction in their geographic ranges from the Dicellograptus complexus Zone to the Paraorthograptus pacificus Zone, probably because of the contractions in the distribution areas of the coeval marine sediments. A substantial reduction in the distributions of most diplograptine taxa from the P. pacificus Zone to the Metabolograptus extraordinarius Zone mainly represents the effect of the major extinction event. Our study also demonstrates a reduction in the geographic ranges of each taxon to the center of the Yangtze epicontinental sea during the HME. The changes in geographic ranges are mirrored by a similar reduction in species-level total diversity during the study interval.