Document Type
Thesis
Abstract
Recent studies of extinction in the fossil record indicate that morphological selectivity can drive evolutionary trends. These investigations have focused primarily on specific morphological traits, and none have directly analyzed the role of morphological variability in promoting survivorship. This study seeks to examine morphological variability, body size, and survivorship in veneroid bivalves during the Plio-Pleistocene extinction in Florida. The Plio-Pleistocene extinction (1.8 Ma) occurred in response to global cooling and changes in ocean circulation possibly related to the emergence of the Isthmus of Panama. Stratigraphic occurrences of veneroid bivalves were compiled from the literature to determine victim and survivor species. Fourteen pairs of species from the same genus or closely related genera were selected for study, each containing one extant species and one species that became extinct during the event. A total of 1429 specimens representing 27 localities were examined from collections at the Florida Museum of Natural History and the Virginia Museum of Natural History. Specimens were sampled from the Pinecrest Beds, the Caloosahatchee Formation, the Jackson Bluff Formation, and the Nashua Formation in Florida. Specimens were identified to the species level and digitally imaged. Landmark coordinate points for morphometric analysis were collected from the hinge, the adductor muscles, the pallial line, and along the shell outline at points representing maximum length and height. Generalized Scaled Procrustes was applied to assess morphological variability and centroid size was calculated to quantify body size. The relationships among morphological variability, body size, and survivorship were assessed using both parametric and non-parametric statistical tests. Results indicate that survivor species have significantly higher morphological variability than victim species. Allometric growth and sampling range do not significantly affect this pattern. A locality-controlled comparison of victims and survivors found no statistically significant differences in morphological variability, possibly indicating that differences in morphological variability are due to ecophenotypic variation. Body size does not appear to significantly affect survivorship in veneroid bivalves. These results suggest that morphological variability may be a significant factor in promoting the survivorship of species.
Date Awarded
2006
Department
Geology
Advisor 1
Rowan Lockwood
Recommended Citation
Kolbe, Sarah Elizabeth, "Morphological Variability, Body Size, and Survivorship in Veneroid Bivalves During the Plio-Pleistocene Extinction in Florida" (2006). Geology Senior Theses. William & Mary. Paper 164.
https://scholarworks.wm.edu/geologyseniors/164
