Geographic and temporal patterns of evolution and extinction of brachiopods through the late Paleozoic ice age: Global and regional patterns

The serial pattern of mass extinctions and rebounds that characterized the Paleozoic history of marine invertebrate diversity was interrupted in late Paleozoic time by a long interval of weak diversification and unusually low rates of origination and extinction. This interval of sluggish macroevolution coincided precisely with the most extensive glaciation of the Phanerozoic Era, the late Paleozoic ice age. Using a database of geographic and stratigraphic occurrences of brachiopod genera, I show that climatic conditions of the late Paleozoic ice age caused low macroevolutionary rates by altering the biogeographic composition of the global brachiopod fauna. The onset of cold and highly seasonal temperatures in late Mississippian time caused the preferential extinction of brachiopod genera with narrow latitudinal ranges, which lived primarily at low latitudes and were therefore adapted to only small seasonal temperature changes. It was not until the late Paleozoic ice age waned in middle Permian time that narrowly-distributed genera were able to re-evolve at low latitudes and return the brachiopod fauna to its pre-ice age configuration. Because latitudinal range size was correlated with temporal duration, the preponderance of widespread genera with long average durations during the ice age caused macroevolutionary rates to fall and remain low while the glacial climate persisted. These data also demonstrate the causal linkages between climate and latitudinal gradients of diversity, latitudinal range size, and macroevolutionary rates for brachiopods during late Paleozoic time, and suggest that these same factors underpin the modern latitudinal diversity gradient of marine genera.; Further analyses of brachiopod genera from Mississippian strata of the Central Appalachian basin reveal that the Late Mississippian mass extinction did not strongly select against genera because of their species diversity, regional relative abundance, body size, preferred facies, or environmental breadth. Mass extinctions in general did not select for traits known to influence background extinction rates; however, they did intensify background rates of extinction. This paradox can be reconciled for the Late Mississippian mass extinction because one trait, thermal tolerance, was amplified in importance during the glacial climate. This selective regime lasted through the glacial climate and underpinned the whole of the late Paleozoic ice age.