METABOLISM IN A CHANGING OCEAN: EXTINCTION SELECTIVITY DURING HYPERTHERMAL EPISODES IN THE FOSSIL RECORD

Climate change is believed to be a major driving mechanism behind mass extinctions. Warming and associated hypoxia during episodes of rapid climate warming, dubbed ‘hyperthermals’, are expected to have had drastic and far-reaching consequences for marine faunas—as water temperatures rise and oxygen solubility decreases, the metabolic rates and consequently oxygen demands of organisms increase. For a habitat to be metabolically viable, the rate of supply of environmental O₂ must exceed the resting metabolic demand of organisms. This ratio, dubbed the metabolic index, is a major constraint on the distribution of viable habitat for marine organisms, especially in a changing climate.

Here, we explore the effects of metabolism on extinction selectivity in gastropods and bivalves during post-Paleozoic hyperthermal episodes. We estimate metabolic rates using a general model of metabolism based on biomass and temperature, originally derived by Gillooly et al. (2001). Included are genera from the Paleobiology Database (PBDB) for which body size (maximum log-volume by genus) data are available in Payne and Heim (2020) and for which taxon-specific metabolic rate coefficients have been determined (Vladimirova 2001; Vladimirova et al. 2003), applied at the finest taxonomic resolution possible up to the ordinal level. Paleotemperatures at the location of each taxon occurrence in the PBDB are obtained from HadCML3 climate model outputs. Following the approach of Reddin et al. (2020), we synthesize across multiple binomial regression models using these metabolic rate estimates to calculate relative hyperthermal vulnerability (RHV), the difference between the likelihood of extinction during hyperthermal events and baseline extinction probability, in order to determine how an organism’s metabolism may affect patterns of taxonomic extinction and survival across hyperthermal-driven extinction events. Understanding the potential responses of modern fauna to rapid episodes of warming remains incredibly topical, especially with regards to current projections of the rate and magnitude of anthropogenic climate change.