220-4 Ostracod Evolutionary Tradeoffs in Response to the Paleocene-Eocene Thermal Maximum (PETM)

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

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Abstract:

Ostracods are highly sexually dimorphic microbenthos that are some of the few multicellular fossils that range through early Cenozoic hyperthermals, such as the Paleocene Eocene Thermal Maximum (PETM) (Hunt et al, 2017). The record of the PETM in the Atlantic Coastal Plain has excellent geochemical proxies, but fewer studies on how these environmental changes affected ecosystems and organism’s evolutionary trajectory.  We measured size and length to width ratio amongst male and female adult ostracods to see if sexual dimorphism decreased with increased stress due to high water temperatures. Shell formation is one of the most energy expensive maintenance processes in ostracods, and can be reduced without directly compromising survival. However, shells provide protection from predators and display male sexual fitness (Fernandes et al. 2018). We found that sexual dimorphism lessened after the carbon isotope excursion (CIE), as male ostracods experience metabolic burden on making large tests. We found that this trend encompassed community change (in that species with less extreme sexual dimorphism made up a larger part of the community post- PETM than pre-PETM) and evolutionary change in single species.

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

doi: 10.1130/abs/2025AM-11301

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