NEW PERSPECTIVES ON THE SIGNIFICANCE OF THE MULTI-PHASED PLIENSBACHIAN/TOARCIAN EXTINCTION ON REEF ECOSYSTEMS

Most geoscience research on extinctions and environmental perturbations has focused on the five largest biotic crises of the Phanerozoic, the “Big 5”. Nevertheless, research on mass extinctions that are less severe has yielded important information about biotic turnover, collapse of different paleocommunities, and recovery from severe paleoenvironmental perturbations. Our research in the Atlas Mountains of Morocco on the Pliensbachian/Toarcian extinction and subsequent Toarcian Oceanic Anoxic event (Early Jurassic) reveals that this interval of time was particularly catastrophic for corals and reef ecosystems. A revised and greatly expanded taxonomy of Tethyan coral faunas reveals 49% extinction at the genus level and 91% extinction at species level across both events. This massive coral extinction is paralleled by the loss of lithiotid bivalves at the Toarcian Oceanic Anoxic Event and one of the five largest reef collapses (by volume) of the Phanerozoic. The devastation during the late Pliensbachian and early Toarcian biotic crisis suggests that this interval is potentially the most important extinction event for scleractinian corals and fundamentally shaped the future of diversity and morphological disparity within the later Mesozoic coral clades. Consequently, this interval should be considered a key period in the evolutionary dynamics of scleractinian corals and reef ecosystems more broadly. Despite these extinctions, coral reefs recover relatively rapidly in Morocco and so these data on coral and reef survival and recovery during the Early Jurassic event are particularly pertinent for questions about present day ecosystem collapse and conservation of coral habitats.