DRIVERS OF CEPHALOPOD BIODIVERSITY DURING A CRITICAL INTERVAL OF EARTH HISTORY (Invited Presentation)

The Cenomanian and Turonian stages of the Late Cretaceous represent a critical interval of Earth history. Greenhouse warming led to marked sea level rise, the formation of broad epicontinental seaways through the Cenomanian, and initiation of Ocean Anoxic Event 2 (OAE2) in the latest Cenomanian. A global database of cephalopod occurrences is used to determine how these environmental perturbations affected standing diversity, speciation, and extinction of this important marine animal group. Origination and extinction patterns varied regionally, with some clades experiencing endemic radiations within epicontinental seaways while others expanded their geographic ranges. Globally, species with larger geographic ranges had lower extinction rates throughout the C-T interval. The high-resolution record within the Western Interior Seaway (WIS) of North America permits a more detailed analysis of cephalopod diversity dynamics. Integrating cephalopod occurrences with a paleoceanographic model for the WIS during OAE2 shows how water mass conditions controlled the distribution of cephalopods within the WIS and how this distribution changed through OAE2. Cephalopod extinctions in the WIS were associated with carbon isotopic excursions throughout the C-T interval as well as with initiation of ocean anoxia and episodes of increased runoff during OAE2. During the peak of OAE2, cephalopod species became restricted to a refugium in the southwest portion of the WIS, then quickly expanded back into the rest of the WIS in the earliest Turonian. With sufficient sampling of cephalopod occurrences and relevant environmental data, ecological niche modeling has the potential to demonstrate how the geographic distribution of suitable habitat changed during OAE2. It could also test whether niches were conserved in specific ammonoid clades and whether endemic radiations of cephalopods within the WIS were aided by partitioning of cephalopod populations into microhabitats. This integrative approach will help constrain drivers of cephalopod diversity through times of environmental crisis.