THE K-PG MASS EXTINCTION DID NOT PERMANENTLY RESTRUCTURE MARINE ECOSYSTEMS

The Cretaceous-Paleogene (K-Pg, 66 Ma) mass extinction event caused the loss of ~76% of marine species globally and it is hypothesised that massive ecological turnover occurred in its wake^1,2. In the marine realm, early Cenozoic radiation following the K-Pg led to the appearance of many modern species and it has been hypothesised the K-Pg extinction resulted in the emergence of modern marine community structure⁴. Additionally, debate continues as to whether or not the Deccan Traps Large Igneous Province Region (LIP) contributed to this mass extinction by degrading global ecosystems during the latest Cretaceous, or whether effects of volcanism were negligible, leaving the Chicxulub impact as the sole cause of the mass extinction^5,6,7. Here, we show that (i) The K-Pg mass extinction did cause temporary structural shifts in a well-preserved, high latitude marine community at Seymour Island Antarctica, however no changes were permanent; and (ii) The Deccan Traps LIP caused no observable structural changes in Late Cretaceous ecosystems at Seymour Island. Thus, we suggest that broad community structure and function in the marine realm was likely maintained across the K-Pg boundary, despite a major reduction in standing biodiversity. We used a novel trait-based model to reconstruct four food webs across the K-Pg extinction (from the Campanian to the Eocene), using Seymour Island fossil occurrences and associated ecological traits. We compared network metrics and motifs between the food webs, to investigate the effects of both the K-Pg mass extinction and Deccan Traps LIP volcanism on community structure and function. Our findings refute the suggestion that the K-Pg represents a turning point in marine community structure, nor do we deem it the origin of modern marine community structure. Finally, our results indicate the Deccan Traps LIP did not cause any detectable deleterious effects on marine ecosystem structure or function in the latest Cretaceous, lending further strength to the theory that the Chicxulub impact alone caused the mass extinction.