Paleogeography modulates marine extinction risk throughout the Phanerozoic

Understanding the factors that have influenced the intensity and selectivity of extinction throughout Earth history is critical for explaining past biodiversity loss and associated implications for the present biotic crisis. Here, we investigate the role of coastline geometry and paleogeographic boundary conditions in shaping extinction risk for shallow-marine-restricted taxa across 540 million years of Earth history. Our findings reveal that interactions between the geographic distributions of taxa and the geometric configurations of continental margins significantly predict relative extinction risk throughout the Phanerozoic: taxa with longer potential dispersal pathways, often associated with east-west oriented coastlines, islands, or inland seaways, consistently exhibit higher extinction risk than taxa with shorter potential dispersal pathways. In contrast to many other predictors of extinction risk, dispersal distance selectivity is amplified during mass extinction events and hyperthermal intervals, suggesting geographic constraints become more important during periods of rapid climate change. Our results provide another potential mechanism for the generally elevated extinction rates during the Paleozoic, an interval characterized by complex inland seas and a preponderance of east-west coastlines. These insights underscore the importance of considering paleogeographic context when interpreting extinction patterns and assessing implications for future biodiversity loss.