ECHINOID FAUNA OF THE LOWER PLEISTOCENE WACCAMAW FORMATION

The lower Pleistocene Waccamaw Formation of northeastern South Carolina and southeastern North Carolina is recently understood to contain at least ten species of echinoids making it the most diverse Pleistocene echinoid fauna along the east coast of North America. An exposure along the Intracoastal Waterway in North Myrtle Beach, South Carolina displays the basal bed of the unit with an exceptionally diverse echinoid assemblage. A new species (Encope dubarorum) recently described by some of the authors has attributed to this increase in local diversity. Additionally, the variable morphologies of Mellita caroliniana may either represent other new species or a single, highly-plastic species. These two recognized species are abundant components of the Waccamaw Formation, occurring more frequently within the basal shelly, calcareous sand of this unit. Together, they both account for over half of the relative abundance of echinoid species.

In addition to the general morphology of these echinoids, their oral plate sutures and patterns are diagnostic and used to distinguish closely related species. Given that E. dubarorum is an exceptionally robust, thick margined species, with a somewhat inflated oral surface, the oral suture plates and patterns were not easily discerned. The visibility of these sutures were enhanced by gentle polishing with carbide and subsequent staining with a mixture of Alizarin Red S and potassium ferricyanide. In future studies, such stains may be applied to better observe plate margins and suture patterns.