DIVERSIFICATION THROUGH GLOBAL COOLING: DECOUPLED RESPONSES OF MARINE BIVALVE ORIGINATION AND EXTINCTION TO CHANGES IN CENOZOIC TEMPERATURE

The accumulation and loss of diversity within animal clades depends on a multitude of biotic and abiotic factors. Teasing apart the relative contributions of these factors enables a more precise estimation of biodiversity response to biological and environmental perturbations. Aiming towards this coupled biotic and abiotic model of diversification dynamics, we analyze the relation between a major abiotic factor, temperature, and the two components of diversification, origination and extinction.

Using the rich Cenozoic fossil record of marine bivalves and multiple Cenozoic climate proxies from the marine record, we examine the correlation of both origination and extinction with two aspects of climate dynamics within geological stages: the mean temperature state and the magnitude of the linear rate of temperature change. We account for variable stage duration by first modeling the relationship between stage duration and per-capita origination (strongly correlated) and extinction (not correlated but still positive), then using the residuals from that relationship to derive the expected excess or dearth of origination and extinction in a stage given its duration.

We find that global per-capita origination tends to increase in warmer mean temperature states, though the effect is damped as linear rates of temperature change increase. In contrast, per-capita extinction tends to increase with higher rates of temperature change, and appears to be unaffected by the mean temperature state. Suspension-feeders drive the extinction pattern, with other trophic groups unrelated to the climate signal, possibly suggesting phytoplankton responses to climate as a factor. Although this extinction pattern is largely a product of cooling through the Cenozoic, the few episodes of warming also correlate with elevated rates of extinction–a sobering result considering the pace and mode of projected climate change into the future.