Publication Date


Document Type


Committee Members

Burt Carter (Committee Member), Charles Ciampaglio (Committee Chair), David Dominic (Committee Member)

Degree Name

Master of Science (MS)


The Late Eocene echinoid, Periarchus lyelli (Conrad, 1834), known for its wide geographic range, high abundance, and specific stratigraphic range, is an ideal example of a guide fossil. However, due to its highly variable test morphology, many have questioned if, in fact, this sand dollar is actually two or three distinct species that have been misclassified. A preliminary study on this subject has been performed on specimens from Mississippi, North Carolina and South Carolina (Williamson, 2006), showing significant separation in test shapes. Continuing previous research, this study analyzes the test shapes of P. lyelli over its entire North American geographic distribution. Multivariate statistical techniques combined with substrate and structural analysis support the idea of three species instead of one in the case of P. lyelli. This examination of P. lyelli provides insight to the precise classification of the sand dollar and the difference between interspecies variation and intraspecies variation.

Page Count


Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded