DOES THERMAL TOLERANCE MEDIATE EXTINCTION RISK OVER THE PHANEROZOIC?

Thermal tolerance is an important determinant of extinction risk for species in the modern. However, little is known about the importance of thermal tolerance in predicting extinction risk over the Phanerozoic relative to other determinants of extinction risk, such as body size and geographic range size. We investigate the selective signature of thermal tolerance over the Phanerozoic, focusing on median occupied temperature and realized thermal range for marine invertebrate genera. Thermal tolerances were quantified using the HadCM3 coupled-atmosphere-ocean generalized circulation model (AOGCMs) for each Stage of the Phanerozoic. Extinction selectivity was estimated for thermal tolerance using a Generalized Linear Mixed-effects Model (GLMM) with Stage and Family as random effects. The model included 400,000 spatio-temporally unique occurrences for over 10,000 marine invertebrate genera from the Paleobiology Database. Both median occupied temperature and realized thermal range were found to be important determinants of extinction risk over the Phanerozoic. To evaluate the relative importance of thermal tolerance compared to other known determinants of extinction risk, we ran GLMMs on all combinations of the following predictors: median occupied temperature, realized thermal range, geographic range size, and body size. The best-supported model, based on Akaike’s Information Criterion (AIC), included all four variables, highlighting the importance of a multivariate approach when evaluating extinction risk over the Phanerozoic. Our results also suggest these predictors should be considered together when identifying at-risk taxa today.