A COMPUTATIONAL APPROACH TO QUANTIFYING MORPHOMETRIC DIFFERENCES IN PLANKTONIC FORAMINIFERA; A CASE STUDY FROM THE CRETACEOUS WESTERN INTERIOR SEAWAY DURING OCEANIC ANOXIC EVENT 2

Foraminifera are marine protists that mineralize a calcareous shell (or test). As heterotrophs, changing oxygenation and trophic conditions influence their metabolism, their body size, and the shape of their test’s constituent chambers. However, recent studies on foraminifera have revealed that changes in test morphology in response to shifts in oxygenation are not fully understood. To test multiple drivers of variation, we employ a comparative morphometric analysis of assemblages of fossil planktonic foraminifera from two different localities within a single basin. Specifically, we examine assemblages from the Late Cretaceous U.S. Western Interior Seaway (WIS) during Oceanic Anoxic Event 2 (OAE2), an ancient interval of global environmental change. The event is well defined within the strata of the WIS and is associated with shifts in ocean oxygenation and productivity. In this study, we use carbon isotope chemostratigraphy to compare specimens from central New Mexico and northeastern Kansas before, during, and after OAE2. Assemblages were imaged and batch processed through AutoMorph software to measure the body size of thousands of individual specimens. Preliminary data shows differences in major axis length based on locality, where specimens from the eastern margin of the seaway are generally larger than specimens from the western margin. Although we do not find evidence for a strong temporal driver of morphological change, we do detect subtle differences in body size in response to OAE2 at both localities. We interpret these preliminary findings to support the hypothesis that the eastern and western margins of the seaway were dominated by distinct water masses and to indicate that water mass oxygenation is a primary driver of body size shifts. This study showcases the utility of foraminiferal morphology as a geologic archive and demonstrates the necessity of re-exploring preexisting collections, in this case micropaleontological slides, with computational approaches to glean greater ecological meaning.