GLOBAL DISTRIBUTION PREDICTS REGIONAL GEOGRAPHIC RANGE AND LONGEVITY IN MARINE GENERA OF NORTH AMERICA

Geographic range is a good predictor of extinction susceptibility of genera, but the determinants of geographic range are poorly constrained. Using an integration of the Macrostrat (http://macrostrat.geology.wisc.edu) database of North American geology and the Paleobiology Database (http://paleodb.org), we show that non-endemic genera across a wide range of Linnaean classes have longer durations and wider geographic ranges within North America than do genera endemic to North America. Previous explanations for longevity and geographic range in the fossil record have focused on larval dispersal. However, our new results suggest that within-region environmental breadth may contribute to both broad geographic range and decreased regional extinction risk.

The Macrostrat database provides two important advantages over other studies of geographic range based solely on the Paleobiology Database or similar compilations: we can account for the area of preserved marine sediments and we can estimate rates of environmental change. The spatially explicit structure of Macrostrat allows us to measure geographic range as the proportion of available marine sediments occupied by each genus. Macrostrat also allows us to quantify the rates of marine sediment expansion and contraction in a way that is analogous to genus origination and extinction rates. Thus we are able to measure the extinction responses of endemic and non-endemic genera to pulses of marine sediment contraction (i.e., sea level fall). We find that non-endemic genera have a significantly lower rate of regional extinction than endemic genera during episodes of marine regression.

Our results are robust to variations in sampling intensity and show that non-endemic genera persist longer, occupy a large proportion of available marine sediments and occupy a larger number of habitat types within North America than their endemic counterparts. In conclusion, we demonstrate that habitat breadth is likely to have exerted a strong influence on stratigraphic durations and the regional and global distributions of marine genera.