Publication Date

Spring 2022

Degree Type


Degree Name

Master of Science (MS)




Carlie Pietsch

Subject Areas



The Gulf Coastal Plain, in the southeastern United States, contains several sites with well-preserved fossil assemblages from the Cretaceous- Paleogene boundary (K/Pg). Changes in benthic macroinvertebrate assemblages after mass extinction events commonly include reduction in body size of surviving organisms and preferential survival based on ecospace occupation. This study examines patterns of functional ecology and body size change in mollusk fossils from bulk samples collected throughout the post-extinction recovery interval at a well-studied boundary site from Darting Minnow Creek in Brazos, Texas USA and a recently described K/Pg boundary section on the Ouachita River in Malvern, Arkansas USA. The proportional abundance of mollusk ecological life modes at Malvern, AR shows a shift from an assemblage dominated by immobile, epifaunal suspension feeding oysters in the first 1.5 meters of the Paleogene to a community composed of mobile, infaunal, suspension and deposit-feeding bivalves. The change from a disaster assemblage to a recovery assemblage is consistent with previous community ecology studies documenting the recovery from the end-Cretaceous mass extinction. The shift in functional ecology is matched by a significant increase in bivalve body size and is interpreted as an increase in the available energy from primary productivity at this site. The disappearance of oysters suggests additional changes to the substrate, sedimentation, and/or freshwater input. Across the U.S. Gulf Coastal Plain, both sites show evidence of multiple stages in the recovery of diversity, ecological complexity, and body size of the benthic mollusk community in the aftermath of the K/Pg.