IMPROVING OUR UNDERSTANDING OF BRITTLE STAR (OPHIUROIDEA: ECHINODERMATA) BIODIVERSITY: RECONCILING DISARTICULATED SKELETAL ELEMENTS WITH ARTICULATED SKELETONS

Paleozoic brittle star biodiversity is both poorly documented and poorly understood. Brittle stars are echinoderms that easily disarticulate into many individual skeletal elements. Previous studies of Paleozoic brittle stars have relied heavily on fully articulated skeletons which are biased to those faunas, environments, and taxa with excellent preservation. Studies of Mesozoic and Cenozoic brittle stars focus on disarticulated skeletal elements collected from poorly lithified sediments. Weathered shale collected from the Upper Mississippian (Chesterian) Big Clifty Fm. in Sulphur, IN and the Glen Dean Fm. in Hopkinsville, KY bears relatively high brittle star generic diversity (at least six taxa). Preliminary analysis has proposed the presence of two furcasterid-type taxa, one eospondylid, one modern-type taxon (possibly Aganaster), one Onychaster-like taxon, and one Cholaster?-like taxon; however, specific genera and species assignments is currently unknown.

To better constrain the generic and species identification of these disarticulated skeletal elements, a morphological character suite modified from studies of Mesozoic brittle stars was constructed. These characters encompass features of the brittle star vertebrae (fused paired ossicle that core the arm) and lateral arm plates (ossicles on the side of the arm that bear spine articulations) including: muscle scars, vertebrae articulation processes, lateral arm plate general outline, inner and outer shape, ornamentation, and spine articulations. The character suite will be utilized to analyze the five genera of disarticulated vertebrae and six genera of disarticulated lateral arm plates in addition to published Mississippian-aged brittle stars housed in museums. Reconciling disarticulated brittle star skeletal elements to articulated skeletons will improve our knowledge of Paleozoic brittle star biodiversity, and increase our understanding of brittle star evolutionary relationships, biostratigraphy, paleoecology, and paleobiogeography during an important time in Earth’s history.