Biodiversification of Late Ordovician Hirnantia fauna on the Upper Yangtze Platform, South China

The Hirnantia Fauna is a globally-represented, cool water brachiopod fauna that originated and flourished in shallow marine environments at intermediate to low latitudes after the first episode of the end-Ordovician mass extinction. It was well-developed, widely distributed, long in stratigraphical range, and complex in palaeoecological differentiation on the Upper Yangtze Platform of the South China paleoplate, where it has been extensively studied. Qualitative and quantitative analyses show that the FAD of the Hirnantia Fauna in South China becomes stratigraphically higher from nearshore to offshore localities on the Yangtze Platform, while the range of the fauna becomes shorter whereas the taxonomic diversity increases. Over its stratigraphical range the diversity of the Hirnantia Fauna at nearshore localities consistently decreases, but trends in the opposite direction at offshore, deeper water localities. The fauna was represented by different communities, subcommunities or associations with changing environmental factors (such as water depth and substrate) at different localities or horizons.