Manual and landmark-based morphometric comparison of two populations of Campeloma, sp. across the K-Pg boundary

Understanding how species survive mass extinction events allows scientists to more fully explore the effects of major biotic change in the fossil record. The Cretaceous-Paleogene (K- Pg) extinction 65.5 Ma was one of the largest extinction events in Earth's history and profoundly affected both terrestrial and marine life. Fossiliferous exposures of the Hell Creek and Fort Union Formations in the northern Great Plains of the western U.S. offer some of the best available records of conditions before and after the K-Pg boundary. Similarly, due to their hard aragonitic shells, conispiral geometry, and prevalence throughout the Phanerozoic Eon, well- preserved gastropods (snails) are perfect candidates for morphometric and stable-isotope analyses aimed at reconstructing paleoecological information.
In this study, I compared two populations of the freshwater gastropod <em>Campeloma sp.</em>, one from before and from after the K-Pg boundary at Hell Creek, Montana. I used principal components analysis (PCA) of 6 manually measured and 10 landmark-based components of shell morphological variation to compare the two populations, in order to investigate any possible anatomical differences that may have arisen in response to the extinction event. Likewise, I used stable oxygen isotope analysis to investigate potential differences in ontogeny or growth rate. Taken together, the stable isotope and morphometric analyses suggest that <em>Campeloma sp. </em>exhibited no major ontogenetic or anatomical differences in response to the events that triggered the K-Pg extinction. This suggests that <em>Campeloma </em>was capable of withstanding dramatic environmental change with little to no adaptation in shell morphology.