MORPHOMETRICS OF FOSSIL MERCENARIA SHELLS FROM THE MID PIACENZIAN WARM INTERVAL AND THE SUBSEQUENT EARLY PLEISTOCENE COOLING, MID ATLANTIC COASTAL PLAIN

The study of fossil bivalves provides valuable information on the influence of paleoenvironmental and paleoclimatic conditions on shell growth in a context that can be useful for conserving modern bivalve populations in the face of climate change. The hard clam, Mercenaria, is economically important and a common constituent of fossil deposits along the Mid Atlantic Coastal Plain (MACP). Here, we investigate whether shell shape is influenced by warm vs. cold climate state. To achieve this goal, we analyze changes in the morphology of fossil Mercenaria shells from the Mid Piacenzian Warm Interval (MPWI) and early Pleistocene cooling. We hypothesize that there is greater disparity in morphology between shells from different paleoclimates than populations within the same climate state. We analyzed the length of corporeal characters (n = 8) in 45 right valves from 2 North Carolina localities: MPWI (Duplin Formation, Robeson Farm) and early Pleistocene (Lower Waccamaw Formation, Register Quarry). All characters were normalized to shell length to eliminate size bias. Preliminary results based on ANOVA scores show significant differences among 2 of the characters (height: F = 14.12, p-value < 0.001, α = 0.05; and length of posterior cardinal tooth: F = 6.62; p-value = 0.01; α = 0.05). Future work will incorporate additional Mercenaria specimens from other MPWI and early Pleistocene localities in North Carolina and Virginia.