ASSESSING THE PALEONTOLOGICAL UTILITY OF GEOMETRIC MORPHOMETRICS FOR DELINEATING SAND DOLLAR SPECIES: A PRELIMINARY ANALYSIS OF THE GENUS ENCOPE

Encope is a sand dollar genus restricted to the New World. Encope fossils date back to the Middle Miocene, with extant species originating in the Pliocene or Pleistocene. Of the six extant Encope species that can be found in the Atlantic and Gulf coasts of North America; E. aberrans and E. michelini are also found in the fossil record. Although E. michelini can be distinguished from E. aberrans by its five nearly equal-sized ambulacral notches at the ambitus and its larger anal lunule in the posterior interambulacrum, the differentiation of E. aberrans from E. michelini has proven difficult as E. aberrans has often been misidentified in the literature as E. michelini or E. emarginata and E. michelini as E. aberrans or E. emarginata. The primary objective of this pilot study was to evaluate the suitability of landmark-based geometric morphometrics for differentiating E. michelini from E. aberrans. Our long-term goal is to augment standard qualitative taxonomy with quantitative approaches to improve the delineation of fossil echinoid species. Samples were collected in three different localities in Florida (Carrabelle, Cedar Key, and the Florida Keys) along 20m transects. Invertebrate paleontology collections of the Florida Museum of Natural History were used to supplement the sample size. All specimens were photographed with a GSA scale. Thirty-two landmarks were digitized on the aboral side of the specimens using tpsDig and the data were successively subjected to Procrustes transformation with MorphoJ. Subsequently, a principal component analysis (PCA) was performed to determine the linear combinations of variables that explain the majority of the variation in the data. The PCA revealed clear separations between the species, with some intra-specific variation likely due to site-specific or population-specific factors. Much of the interspecific variation was primarily observed in the ambulacral notches. To evaluate the intra-specific variation, additional specimens will be analyzed in the future. The results of this study indicate that landmark-based geometric morphometrics can help to differentiate E. michelini from E. aberrans. Understanding the evolution and systematics of Encope offers valuable insights in conducting broader ecological and evolutionary studies.