220-2 Climate-Driven Morphological Changes in Eocene Taxa on Seymour Island, Antarctica

Session: Life and Environments Through Time and Space: Multi-Record Approaches to Stratigraphic Paleobiology (Posters)

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Abstract:

Climate change plays a large role in controlling diversity, which can be tracked throughout time. The Eocene marks the onset of global cooling, and the well-preserved contemporaneous mollusk communities from Seymour Island, Antarctica provide us with the opportunity to examine marine mollusk communities throughout this time period. We hypothesize that this climatic shift is reflected in corresponding morphological changes within these communities, as taxa adapt to the harsher environmental conditions associated with the colder intervals. In this study, we use geometric morphometrics to quantify the morphological variation through the Eocene in three mollusk genera: the bivalves Eurhomalea sp. and Saxolucina sp., and the gastropod Polinicies sp. 

The examined material is from the La Meseta Formation on Seymour Island, Antarctica. This material includes all six stratigraphic units, ranging from Telm 2 to Telm 7. The materials are housed in the Paleontological Research Institute in Ithaca, NY, and the Florida Museum of Natural History Collections in Gainesville, FL. In total, we photographed over 1000 specimens across all six Telms. 

All specimens were digitized, including the placement of homologous landmarks, such as e.g., hinge teeth in bivalve or the apex and umbilicus in the gastropods, and semilandmarks were used to capture shell outlines of all three groups. These steps were performed in tpsDig2 and tpsUtil. The landmark data was scaled, translated, and rotated with Procrustes fit, then analyzed with a Principal Components Analysis using the software package MorphoJ.

Our analysis shows an overall decline in morphological diversity within these groups as temperatures decrease. Among the bivalve taxa, we observed a trend toward rounder shell shapes and a reduction in number of specimens with more ellipsoid morphologies. A similar pattern is evident in the Polinices samples. This shift toward more compact forms with a lower surface area-to-volume ratio could indicate an adaptive response to cooler temperatures, potentially as a strategy to minimize heat loss.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9489

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