QUANTIFYING THE MORPHOLOGY AND RECONSTRUCTING THE PHYLOGENY OF VENERICARD BIVALVES ALONG THE GULF COASTAL PLAIN DURING THE PALEOCENE AND EOCENE

Recent projections of anthropogenically-influenced climate change have emphasized the importance of understanding how organisms respond to long-term climate change, using data from the fossil record. Recent studies have focused primarily on quantifying the ecological and biogeographic effects of climate change, with relatively little attention paid to the evolutionary responses of faunas. The goal of this research is to explore whether the evolutionary history of planicostid venericards was significantly impacted by Paleogene climate change along the U.S. Gulf Coastal Plain, focusing specifically on the Paleocene-Eocene thermal maximum, a 200,000 year interval of rapid warming. To do this, we have reconstructed venericard phylogenetic history, quantified morphology, and compared both to records of climate change during the Paleocene and Eocene.

Planicostid venericards are abundant, diverse, and often well-preserved throughout the Paleogene units of Alabama and Mississippi. We collected specimens from eleven field sites in Alabama and Mississippi and augmented these with specimens from the Smithsonian Museum of Natural History, the Virginia Museum of Natural History, the Paleontological Research Institute, and the Mississippi Department of Environmental Quality. Species examined include Venericardia alticostata, V. wilcoxensis, V. planicosta, V. turneri, V. bashiplata, V. nanaplata, V. claiboplata, V. hatcheplata, V. densata, V. aposmithii, and V. mediaplata. We digitized images of venericards in lateral orientation and quantified venericard morphology using thirteen prominent landmarks, distributed along the beak, hinge, adductor muscles, and shell outline. We then reconstructed the phylogeny using 39 characters compiled for 11 ingroup and 4 outgroup taxa. Planicostid venericards have received relatively little taxonomic attention in the past and this research will contribute significantly to our knowledge of venericard systematics. We then qualitatively compared morphological and phylogenetic patterns with paleoclimate data across this interval to explore the evolutionary response of planicostid venericards to climate change. Preliminary results indicate that traditional species designations in this clade appear to be supported by morphometric analysis.