COMPARING THE SHALLOW BENTHIC INVERTEBRATE RECOVERY FROM THE END-CRETACEOUS MASS EXTINCTION AT TWO U.S. GULF COAST SITES

Research on ancient mass extinction events contributes critical understanding of modern ecosystems’ potential responses to extreme stresses. The Cretaceous-Paleogene (K-Pg) mass extinction event, 66 million year ago, is a well-known interval of taxonomic and ecological shifts in both terrestrial and marine communities. This study provides the opportunity to test for differences in functional ecology during the extinction recovery in two distinct shallow marine environments on the U.S. Gulf Coastal Plain.

To examine patterns of ecological change in the Early Danian samples were collected from two K-Pg boundary sites, the Darting Minnow Creek section in Brazos, Texas and the Ouachita River section in Malvern, Arkansas. Both represent shallow marine environments, but the Malvern site was in close proximity to the Late Maastrictian coastline, while Brazos was further offshore. Bulk samples of shallow marine invertebrates were collected from three fossiliferous horizons at Darting Minnow in Texas and at 50 cm intervals for the 4 meters above the K/Pg at Malvern. For each sample, specimens were identified to the lowest possible taxonomic level and were assigned an ecological life-mode (feeding, motility, and position relative to the substrate). Shell volume as a proxy for body size was approximated using length, width, and height for complete fossils.

Fossil preservation at each site was noticeably different, with moldic preservation more common at Darting Minnow and primary shell at Malvern. The total abundance of specimens increased through time at both Darting Minnow and Malvern. Taxonomic richness and diversity increased above the boundary at Darting Minnow. Mean body size increased through the early Danian at both sites. At the Darting Minnow site, the majority of molluscs were epifaunal mobile carnivores and infaunal suspension feeders. At Malvern, preliminary analysis shows the majority of molluscs were epifaunal and infaunal suspension feeders. While some patterns of extinction recovery are similar at the two sites, variation in functional ecology between the two sites is likely caused by environmental differences across the shallow shelf.