PhD Defense - Elvis Guillam

The Late Devonian is marked by two first order extinction events: the Kellwasser event at the Frasnian-Famennian boundary and the Hangenberg event at the Devonian-Carboniferous boundary.

Ostracods, essentially benthic microcrustaceans, were greatly affected at low taxonomic level (species and genera) by these 2 events. Based on a taxonomic study realized on the material from the Blue Snake section and compiled data from the literature, specific extinction rates are estimated at 80% for the Kellwasser event and 69% for the Hangenberg event. Supra-generic levels were poorly affected. These events affected ostracod diversity in various paleoenvironmental compartments (nearshore, outer continental shelf, and bathyal environments) and in numerous geographic areas, demonstrating the global nature of these extinctions.

The recovery of ostracod faunas following these events was certainly influenced by variations in environmental and climatic parameters. It is mainly characterized by the diversification of cosmopolitan taxa, notably within the Bairdiidae and Bairdiocyprididae. The Paraparchitidae also diversified during the Tournaisian (Lower Carboniferous).

The paleobiogeographic distribution of ostracods over the Frasnian-Tournaisian interval suggests that four main factors influenced their distribution. Climate, especially temperature, appears to have influenced the paleobiogeographic distribution of ostracods, with the distribution of identified communities roughly following the latitudinal distribution of climates. Oceanic circulation could explain the affinities observed between faunas from relatively distant geographical areas. The sea level and its variations as well as the dynamics of the tectonic plates seem to have mainly influenced the global connectivity between the faunas of the different geographical areas on a global scale.