Restructuring but no loss of functional diversity at the end-Cretaceous extinction: testing its role in configuring the modern biota

The end-Cretaceous (K-Pg) mass extinction shows how large-scale taxonomic loss impacts 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 surviving the extinction tend to dominate functions today, 66 Myr post-extinction, but both relative richness and phylogenetic structure of those functional groups have been significantly shuffled. Thus, neither 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.