EOCENE FOSSIL DECAPOD CRUSTACEAN DIVERSITY OF THE ATLANTIC COAST OF SOUTH CAROLINA, USA

The middle Eocene formations of the Atlantic Coast have yielded an exceptional decapod fauna. This study focuses on the evaluation of a collection of over 300 specimens of Eocene decapod crustaceans from the Santee Limestone and Tupelo Bay Formation, collected by Billy Palmer in 1996, and housed at Charleston Museum, South Carolina. The rocks of the Tupelo Bay Formation have previously been considered part of the Santee Limestone. Sanders and Katuna (2000) informally proposed that the Cross Member be elevated to the rank of formation, and Geisler et al. (2005) proposed the name Tupelo Bay Formation to incorporate both the Cross Member and Pregnall Member, both previously considered part of the Santee Limestone. Ten families, 15 genera, and 24 species of brachyuran decapod crustaceans, including one new genus and species of Dynomenidae, were recorded from the Santee Limestone and Tupelo Bay Formation. The new genus is morphologically similar to the extant Metadynomene spp. but differs from them in having a pentagonal carapace and poorly defined grooves. The new taxon is one of the few confirmed dynomenid crabs in the fossil record. Five of the genera identified are so-called primitive crabs, 10 are heterotremes, and there are no thoracotremes. Both the Santee Limestone and Tupelo Bay Formation are highly fossiliferous, with an abundant fauna of bryozoans represented by many growth forms; bivalves, especially oysters; gastropods; echinoids; brachiopods; corals; decapods; and some vertebrates. The presence of bryozoans with a high diversity suggests an environment of deposition in subtropical, clear water at shallow shelf depths. The decapods preserved in the limestone usually consist of fragmented carapaces, chelipeds, or leg parts resulting from deposition in a moderate energy environment, strong enough to disarticulate the carcasses but not to destroy the remains. Museum work funded by NSF EF-0531670 to Feldmann and Schweitzer.