EOCENE FOSSIL DECAPOD CRUSTACEAN OF THE ATLANTIC COAST OF SOUTH CAROLINA, USA – PRESERVATION TYPES

The middle Eocene formations of the Atlantic Coast have yielded an exceptional decapod fauna. The vast majority of the fossils from carbonate facies in eastern North America have been collected from the Santee Limestone and Tupelo Bay Formation of South Carolina and the Castle Hayne Formation of North Carolina. 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 the Charleston Museum, South Carolina; a smaller, private collection of about 50 specimens of Gale A. Bishop; and material collected by us.

The relatively high diversity of decapods in the Santee Limestone and Tupelo Bay Formation of South Carolina can be interpreted as resulting from depositional environments in clean water at shallow shelf depths. The decapods typically consist of fragmented carapaces, chelipeds, or leg parts resulting from deposition in a moderately high energy environment, strong enough to disarticulate the remains but not to destroy them (Bishop and Palmer, 2006). The decapod fossils described here are mostly small, well preserved carapaces with a thin, white layer of cuticle.

Studies of decapod cuticle focuses on understanding cuticular construction and calcification. The exocuticle and endocuticle in living decapods show a great variability in the distribution of the mineralization (Waugh, 2002). This variation is controlled by the molting cycle that occurs more frequently in juvenile crabs than in adults. Death and burial at different stages of the molt cycle can affect the quality of preservation (Waugh et al., 2009). Some of the specimens retain a chalky cuticle that is easily removable, whereas others have well preserved cuticle. Just one species, Martinetta palmeri Blow and Manning, 1996, has the venter preserved. This may be because of the greater degree of calcification in this species of crabs or because of its larger size. The presence of chalky cuticle on some of the specimens can be a result of alteration due to exposure of the fossils for a long period of time or due to water infiltration in porous limestone. Museum work funded by NSF EF-0531670 to Feldmann and Schweitzer.