THE INFLUENCE OF SEASONAL TEMPERATURE VARIABILITY ON SURVIVAL DURING BACKGROUND AND MASS EXTINCTIONS

Many mass extinctions coincided with rapid temperature warming caused by flood basalt eruptions. Although selectivity during these multi-stressor extinctions included a strong taxonomic component, arising from differences in organism physiology, the role of physiological plasticity is harder to assess in fossil organisms. In modern oceans, organisms that inhabit areas with greater inherent seasonal temperature variability either have broader thermal tolerance windows or the ability to shift thermal tolerance, potentially conferring greater capacity for short-term acclimatization and/or long-term evolutionary adaptation in the face of changing temperatures. To test whether environmental variability improved survival during ancient extinctions, we combined Permian-Neogene marine fossil occurrences from the Paleobiology Database with monthly sea-surface temperature data from the HadCM3L climate model, measuring variability as seasonality – the difference between mean warmest and mean coldest month temperatures. The mean seasonality experienced by a genus did not significantly improve the odds of survival, either during background or extinction intervals. However, the maximum seasonality experienced by a genus was more often a significant predictor of survival, but not particularly during extinctions. Although this could suggest that having some representatives in more variable habitats is beneficial, the result is actually driven by differences in geographic range, an important predictor of survival during background intervals. If seasonality was not important, perhaps acclimatization and adaptation are unrelated to environmental variability, unnecessary because of migration, or unimportant relative to physiological differences among groups.