PLANT TAXONOMIC TURNOVER AND DIVERSITY ACROSS THE CRETACEOUS-PALEOGENE BOUNDARY IN NORTHEASTERN MONTANA

The Cretaceous-Paleogene (K-Pg) mass extinction was a pivotal event in Earth history, the latest of five mass extinctions that devastated marine and terrestrial life. Whereas much research has focused on the global demise of dominant vertebrate groups, relatively little is known about local scale changes, particularly among plant communities across the K-Pg boundary. This study investigated a suite of 11 floral assemblages spanning the K-Pg boundary in northeastern Montana constrained within a well-resolved chronostratigraphic framework. We evaluated the impact of the K-Pg mass extinction on local plant communities as well as the timing of recovery after the mass extinction. Our results indicate that taxonomic richness dropped by ~28% from the Late Cretaceous to Paleocene, a moderate decline compared with other records of plants across the K-Pg boundary. We also find that plant taxonomic composition changed; 63% of latest Cretaceous plant taxa disappeared across the K-Pg boundary, and whereas conifer taxa were more likely to survive the K-Pg event, conifers overall declined in abundance. Plant taxonomic richness returned to Late Cretaceous levels within 900 kyr after the K-Pg boundary. Overall, plant communities experienced major restructuring (changes in relative abundance) during the K-Pg mass extinction, even though no large (e.g., family-level) plant groups went extinct and local communities were quick to recover in terms of taxonomic diversity. These results have direct bearing on our understanding of vegetation change during diversity crises, including the differing responses of various plant taxonomic groups to major environmental perturbation, and the spatial variation in extinction and recovery timing.