The end-Cretaceous mass extinction restructured functional diversity but failed to configure the modern marine biota.

The end-Cretaceous (K-Pg) mass extinction shows how large-scale taxonomic loss affects functional diversity over short and long timeframes. In a macroevolutionary model system, we find that, despite losing ~60% of genera and ~20% of family-level diversity, marine bivalves lost only ~5% of their functional diversity, inconsistent with random extinction. Even with evolutionary opportunities presented by a disrupted ecosystem, low-diversity groups prior to the extinction or those originating in the Cenozoic rarely reach higher ranks today, implying long-term diversity ceilings to certain ecological roles. Clades that survived the extinction tend to dominate functions today, 66 million years post-extinction, but both relative richness and phylogenetic structure of those functional groups have been significantly shuffled. Thus, neither the composition of the pre-extinction biota nor the set of taxa that survived the extinction fully accounts for the functional and phylogenetic structure of today's biota. The extinction disrupted Mesozoic biodiversity but did not fully determine the present-day configuration.