Local diversity remained relatively stable across the Great Ordovician Biodiversification Event (GOBE) in South China

The Great Ordovician Biodiversification Event (GOBE) marks one of the most profound radiations of marine life in Earth history. Numerous hypotheses have been proposed for the drivers of the increase in richness during this interval. Distinguishing among these factors requires biodiversity to be evaluated at both local and regional scales across different environments. Here, we compiled a high-resolution, assemblage-level dataset comprising 557 stratigraphic sections and 12,898 fossil occurrences from South China. We integrated these records using a quantitative stratigraphic approach, to examine changes in local (assemblage-level) and regional marine species richness from the Furongian (late Cambrian) to the Middle Ordovician across four depositional environments: littoral, platform, slope, and deep-shelf. We additionally assessed faunal differences across environments and geographic space. Our results suggest regional richness increased four-fold during the GOBE, closely paralleling the spatial expansion of fossil-bearing environments, especially the platform and slope. In contrast, local (assemblage-level) richness remained relatively stable and low through the study interval, despite fluctuations within the slope environment. The taxonomic composition of the platform and slope environments diverged during the GOBE, and spatial turnover increased from the early to late stages of the GOBE. Our findings suggest the expansion of shallow-marine environments tied to increasing sea levels may have been one of the primary drivers of the Ordovician marine biodiversification in South China, with increased faunal differentiation across both environment and space.