Thermal niche determines marine species loss and assemblage succession during Early Jurassic warming pulses

Marine assemblages are expected to undergo substantial reorganization under anthropogenic climate change but some species may be better situated to track their preferred conditions. Assemblage vulnerability can thus be indicated by the thermal niches of its component species. However, the link between this vulnerability and extinction risk of its species is unclear and cannot yet be tested with modern species since widespread climate-driven extinctions are not yet manifest. To address this gap, we inferred fossil species’ thermal niches based on observed distributions on paleoclimate maps over the hyperthermal pulses of the Late Pliensbachian to Early Toarcian. We tested whether species extirpated from fossil invertebrate assemblages after warming, alongside those species that went extinct, were most likely from the pool of species that were above their thermal optima, in contrast to assemblage immigrants. The fossil record has the potential to reveal unique information about natural system responses to climate change. We discuss how much can it tell us about marine ectotherm vulnerability to extinction under climate change.