The Late Cretaceous (Maastrichtian) Coon Creek Formation of Mississippi and Tennessee possesses a diverse and abundant assemblage of decapods including lobsters, ghost shrimp, and crabs. The formation lies in a temporally and paleogeographically significant location, situated between the Atlantic Coastal Plain and the Western Interior Seaway, shortly before the closing of the seaway and the K-Pg Mass extinction.
Coon Creek decapods have been little studied since the fauna was first described in the 1920’s. A large collection of specimens, ranging in preservation from poor to excellent, has recently become available for study. Because of the visible variation in preservation, the abundant material, and the paucity of cuticular data of this type of preservation, an investigative study of elemental composition of the sediment and cuticle of six species of decapod from six families (Palinuridae, Nephropidae, Callianassidae, Dakoticancridae, Raninidae, and Retroplumidae) is conducted using material collected at the Blue Springs Locality in Mississippi.
Cuticle, concretions, decapod burrow, and sediment from the site are analyzed with X-Ray Florescence and Elemental Reflectance for preliminary elemental composition and subsequent mineral composition. Concretions and the burrow were observed in thin section and were mapped for elemental distribution using Energy-dispersive X-Ray spectroscopy and dot mapping. The six species of decapod were analyzed using the same techniques. Taphonomic data supports preservation ranging from well preserved phosphatization to secondary alteration to silica-rich exterior and weathering clay minerals. Because the silica is not replacing the phosphatized exocuticle and microscopic structure of cuticle in cross section is not preserved in the silica layer, the cause of this alteration is uncertain. This preservation is un-like the decapod cuticle preservation of the concretions of the Bearpaw Shale Formation (Late Cretaceous) of Montana.
Species of the Coon Creek Formation were re-assessed and assigned to modern taxonomic schemes. Sixteen species are identified and two new species are described including Hoploparia tennesseensis, Hoploparia mcnairyensis, Linuparus new species, Linuparus sp., Palaeopetrochirus enigmus, Seorsus wadei, Bournelyreidus new species, Cristipluma mississippiensis, Hoploparia georgeana, Mesostylus mortoni, Tetracarcinus subquadratus, Avitelmessus grapsoideus, Cretacoranina testacea, New genus new species (Carcineretidae), Dakoticancer australis, Prehepatus harrisi, and Latheticocarcinus atlanticus. This decapod assemblage shares common species with correlative units of the Western Interior Seaway, the Gulf Coastal Plain, and the Atlantic Coastal Plain, supporting the hypothesis that the Mississippi Embayment is an ecotone for North American decapods.