Biodiversity patterns of Silurian Radiolaria

Data analysis of all published and well-dated Silurian radiolarian localities was conducted with the goal of revealing long-term patterns in Silurian radiolarian biological diversity. The chronostratigraphic distribution of 161 species was compiled from 25 publications, each selected because of their independent age control. The pattern and dynamics of changes in biodiversity are described using indices that allow for the assessment of changes in taxonomic richness through time. Following the Hirnantian (end-Ordivician) mass extinction, the Rhuddanian stage records very low levels of diversity, which then increase gradually throughout the Llandovery series and reach a maximum by the Sheinwoodian stage, before decreasing during the Homerian, and finally, rebounding during the Gorstian stage. The early Silurian (Llandovery) appears to be an interval during which few species went extinct, although the number of last occurrences increases progressively to reach a peak in the Ludfordian. At the same time first occurrences progressively decrease and are relatively low during the Silurian. Only the Gorstian is marked by a sudden increase in origination. The early Silurian is an interval of faunal recovery from the end-Ordovician mass extinction event. Similarly, the Gorstian stage is characterized by a recovery following the Homerian low in radiolarian diversity that may be correlated with the C. lundgreni extinction event, which affected a number of other pelagic groups (e.g. graptolites, acritarchs, conodonts, and chitinozoans), and with the Mulde event, which coincides with a 4.6‰ positive excursion of the δ13C curve.