A Morphometric Analysis of the Highly Variable Clypeasteroid, Periarchus Lyelli
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 from these three states. Continuing the initial research, this study will analyze the test shapes of P. lyelli over its entire North American geographic distribution, along the gulf coast and southern Atlantic coast of the United States. Echinoid test analysis will incorporate multivariate statistical analysis techniques such as Elliptical Fourier Analysis, Procrustes Analysis, and Thin Plate Spline Analysis. In addition to physical examination, substrate analysis will be performed to determine if differences in test shape correlate to differences in lithofacies and paleoenvironmental differences.
The correct classification of index fossils is extremely important for accurate stratigraphic and geologic identification. An examination of the highly variable clypeasteroid, P. lyelli will not only provide insight to the precise classification of the sand dollar, but also the evolution of new architectures and the difference between interspecies variation and intraspecies variation