Regional paleoecology of Permian gastropod genera, Southwestern United States and the End-Permian mass extinction

The high survival rate of gastropod genera during the endPermian extinction (74% vs. 84% overall), their broad distribution, and their ecologic diversity make them an excellent group in which to analyze patterns of survival and extinction. The extraordinarily diverse, well-preserved, silicified gastropod assemblages in the Permian of the southwestern United States are found in basin-fringing carbonate shelves, patch reefs, restricted shelf-basinal carbonates and nearshore, clastic-rich carbonates. Using both field and museum collections I gathered information on distribution and species-richness of 78 genera at 53 localities throughout this province. Three distinct gastropod assemblages were identified using detrended correspondence analysis: a basinmargin assemblage of Leonardian-lower Guadalupian age located in and around the Permian Basin, primarily in the Glass Mountains, a lower Wolfcampian assemblage in the Glass Mountains associated with sponge-algal bioherms, and a carbonate shelf assemblage in southern New Mexico and Arizona of Wolfcampian and Leonardian age. Analysis of the lithotope-dependence, geographic distribution, and species-richness of genera within the province reveals that those genera which survived the end-Permian extinction were characterized by broad environmental distribution within the province and by both broad geographic range and species richness during the midto upper Permian. These characteristics are reflected in the older age of genera that survived the extinction relative to the age of those that went extinct, and suggest that the characteristics that enhanced generic survival during the mass extinction did not greatly differfrom those that enhanced survival during the intervals between mass extinctions.