Document Type
Thesis
Abstract
With global climate shifting at a rapid and unpredictable pace, researchers need additional tools to assess the effects these changes will have on modern organisms. The fossil record can be used to document long-term evolutionary changes in taxa over a variety of ancient climatic events to predict how modern climate change will affect present-day populations. The goal of this study is to quantify trends in size, sha pe, and morphological diversity of the bivalve genus Venericardia from the U.S. Atlantic Coastal Plain in response to global temperature changes over the early Cenozoic. Paleocene, Oligocene, and Miocene specimens were obtained from museum collections, identified to the species level, and photographed in both interior and crosssectional views. The resulting photos were used to collect landmark coordinates, which were the raw data used to quantify mor phology. Landmark data from Eocene specimens were com piled from previous studies, for a total of 848 interior specimens, 541 crosssectional specimens, and 32 species. Body size trends were quantified over time by calculating an average centroid size for each venericard species and subsequently plotting average centroid sizes over time based on species' stratigraphic ranges. To describe shape changes over time, the landmark coordinates were transformed into Procrustes coordinates to remove any variation due to rotation, translation, or size. Principal components analysis was then used to define principal com ponents and create a morphospace, which facilitated comparisons of temporal differences in shell shape. To quantify morphological diversity over time, multivariate variance was calculated using the principal components from the P C A. All three mor phological variables were correlated to global temperature to see if statistically significant relationships existed. Venericard body size is positively correlated with temperature, although a time lag exists between size changes and temperature changes. Venericard shape is also significantly correlated with temperature. Body size and shape do not change significantly over the Paleocene-Eocene Thermal Maximum, but venericards become smaller and more globose in shape with more compact hinges and wider-set adductor muscles after the Eocene-Oligocene cooling. Morphological diversity does not show a strong relationship to temperature, but is more likely related to taxonomic diversity.
Date Awarded
2011
Department
Geology
Advisor 1
Rowan Lockwood
Recommended Citation
Reed, David, "Morphological Trends in Venericardia (Bivalvia: Carditidae) of the U.S. Coastal Plain in Relation to Early Cenozoic Global Climate Change" (2011). Geology Senior Theses. William & Mary. Paper 260.
https://scholarworks.wm.edu/geologyseniors/260
