The first of the five major Phanerozoic extinction events unfolded near the Ordovician/Silurian (O/S) boundary, leading to approximately an 85% decline in marine species. The impact of the extinction varied across higher taxa, with complete loss in some groups, partial declines in many, and others navigating through the end-Ordovician extinctions relatively unscathed. However, the translation of these changes into first-order biogeographic patterns remains elusive. Using network analysis and a large compilation of fossil occurrences, we delineate bioregions of marine invertebrates across the O/S boundary. Simultaneously, by integrating the spatial and temporal dynamics of diverse biological assemblages, including sampling-standardized global diversity, beta diversity, and alpha diversity, we scrutinize how faunal turnover and nestedness influence paleontological spatial patterns. Our findings indicate that the decline in beta diversity during the Hirnantian and Rhuddanian stages was primarily driven by a significant drop in spatial turnover of marine invertebrates. Environmental stress during the main pulses of the extinction even led to an increase in nestedness, mirroring contemporary cases. These results unveil crucial environmental drivers, providing insights into the co-evolutionary mechanisms of life processes and the environment during mass extinctions.
 

Ordovician extinction,network analysis,biogeography,nestedness,turnover