ECHINOIDS OF A MIDDLE TO LATE PLEISTOCENE DEPOSIT FROM THE CENTRAL ATLANTIC COAST OF FLORIDA

Complete tests of three echinoid species were collected from a middle to late Pleistocene deposit at Dickerson Quarry in St. Lucie County, Florida. The sand dollar, Encope michelini L. Agassiz, 1841, the sea biscuit Rhyncholampas sp., and the regular sea urchin Arbacia punctulata (Lamarck, 1816) were present. This is the first record of a regular urchin reported from middle to late Pleistocene sediments in Florida. In addition, it is only the second fossil record of the extant sea urchin A. punctulata. The one previous report, by F.S. Holmes (1860), was derived from Simmons' Bluff, South Carolina. The discovery of Rhyncholampas sp. in this deposit represents the youngest fossil occurrence of the genus in Florida.

Ten complete tests and numerous radioles of A. punctulata were collected along with dozens of complete tests of E. michelini and Rhyncholampas sp. The low number of spines associated with each intact test of A. punctulata, in addition to the presence of the two burrowing echinoid species indicate that the echinoids probably died offshore and were washed inshore where deposition and fossilization occurred. Many of the specimens had barnacles attached to their surface signifying that the tests sat on the seafloor for some time prior to burial. Living specimens of both A. punctulata and E. michelini are found in Florida's coastal waters today, while prior to this study, no known species of Rhyncholampas had survived past the upper Pliocene/lower Pleistocene Caloosahatchee Formation. All three echinoid species were collected from Unit 4 of the Dickerson Quarry. Unit 4 is a sandy coquina limestone layer that is lithologically similar to the Anastasia Formation that is found along much of Florida's Atlantic Coast. A vertebrate faunal assemblage below the echinoid layer helped confirm that specimens in this study are no older than middle to late Pleistocene.