A COMPARISON OF BRITTLE STAR (OPHIUROIDEA: ECHINODERMATA) BIODIVERSITY FROM THE UPPER MISSISSIPPIAN (CHESTERIAN) BIG CLIFTY FM. IN SULPHUR, IN AND GLEN DEAN FM. IN HOPKINSVILLE, KY

Paleozoic ophiuroid biodiversity is poorly documented and taphonomically biased. Previous identification has relied heavily on the study of fully articulated skeletons, limiting our knowledge of individual ossicle morphology and taxonomy. Utilizing techniques common in studies of Mesozoic and Cenozoic taxa has shown surprisingly high generic diversity that was previously undocumented. A study of Upper Mississippian (Chesterian) aged shale washings from the Sulphur, IN locality of Indian Springs Shale Mb. of the Big Clifty Fm. and Hopkinsville, KY locality of the Glen Dean Fm. has recovered a diverse ophiuroid fauna that are taxonomically similar, but show differing abundances among taxa.

Sulphur, IN and Hopkinsville, KY localities are approximately 170km apart with similar megafauna and ophiuroid diversity. Preservation at both locations is pristine with skeletal remains of ophiuroids, edrioasteroids, echinoids, bryozoans, crinoids, and blastoids. However, bryozoans dominate the Hopkinsville megafauna while Sulphur bears a homogenous mixture dominated by disarticulated echinoderm ossicles and is noted for well preserved fish teeth that are uncommon at the Hopkinsville locality. Ophiuroid diversity recovered from both localities is similar with five taxa identified based on disarticulated vertebrae (ossicles coring the arm) and lateral arm plates (bearing spine articulations). Two furcasterid species, one eospondylid species, an Onychaster-type taxon, and a modern type species are represented at both localities; however, species similarities between localities is currently unknown. While faunal similarities are not surprising, there is a discrepancy in taxon abundance, with a dominance of the Onychaster-type vertebrae present at Hopkinsville and minimal lateral arm plates currently found at Sulphur. Additionally, a modern type species discovered at both localities is represented by both vertebrae and lateral arm plates from Hopkinsville, but only by vertebrae from Sulphur sediment. It is currently unknown if these differences result from taphonomic differences or collection bias. Further exploration of isolated ossicles from diversity rich sediment is important in resolving Paleozoic ophiuroid biodiversity worldwide.