Paleogeography modulates marine extinction risk throughout the Phanerozoic

Understanding the factors that have influenced the intensity and selectivity of extinction throughout Earth's history is important for explaining past biodiversity change and forecasting biotic responses to environmental change. Here, we investigated the role of coastline geometry and paleogeographic boundary conditions in shaping extinction risk for shallow-marine taxa over the past 540 million years. We show that interactions between the geographic distributions of taxa and the geometric configurations of continental margins consistently predict relative extinction risk: Taxa with potential dispersal pathways that are long relative to the range of latitude traversed-such as those that occur along east-west-oriented coastlines, islands, or inland seaways-consistently exhibit higher extinction risk than taxa with potential dispersal pathways that provide more direct latitude-traversing paths. This dispersal distance selectivity is amplified during mass extinction events and hyperthermal intervals, suggesting that geographic constraints become more important during periods of rapid climate change. Our results provide another mechanism that potentially contributes to 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 past extinction patterns and provide empirical support for assumptions that underlie extinction risk assessments of extant species.