SELECTIVE SURVIVORSHIP IN THE LATE DEVONIAN: INSIGHTS INTO EXTINCTION DRIVERS FROM INTEGRATED ANALYSIS OF MACROEVOLUTIONARY AND MACROSTRATIGRAPHIC PATTERNS

Patterns of differential survivorship (extinction selectivity) can provide valuable insight into the drivers of extinction events. The Late Devonian bio-crises – encompassing elevated marine diversity losses at the ends of the Givetian, Frasnian, and Famennian stages – have been linked to a variety of potential driving mechanisms, including the expansion of oxygen minimum zones and global cooling caused by the expansion of terrestrial ecosystems. Linking the environmental changes inferred from lithological and geochemical records to extinction selectivity has proven challenging, however, in part because of the need to control for potential biases introduced by the architecture of the stratigraphic record. To address this limitation, we integrated Devonian fossil occurrences from the Paleobiology Database with data on the spatiotemporal and environmental distribution of the North American stratigraphic record from the Macrostrat database. Placing fossil occurrences in a quantitative macrostratigraphic framework allows us to measure the stratigraphic context of genus ranges and determine which of the observed differential extinction patterns are likely to be artifacts of incomplete preservation and which are more likely to represent genuine biological responses to environmental forcings. We find that some selectivity patterns are common to most stages (for example great circle distance, a measure of geographic range, is a highly significant risk predictor most of the time), but that Late Devonian stages also exhibit distinctive selectivity signatures. Mean habitat depth is an important risk factor across both the Frasnian and Famennian boundaries, but the directionality of selection switches from one bioevent to the next: shallow water organisms experience preferential extinction at the end-Frasnian, while deep water taxa are slightly more likely to experience extinction at the end-Famennian. In contrast to other extinction intervals associated with global cooling, extinction risk does not appear to be strongly dependent on latitudinal range during any stage of the Late Devonian. We compare observed selectivity patterns to the extinction patterns predicted by a variety of potential drivers.