Late Paleozoic ophiuroid biodiversity based on a diverse fauna from the Indian Springs Shale Member of the Big Clifty Formation, Sulphur, Indiana, USA

Ophiuroids (brittle stars and basket stars) are a diverse echinoderm group (i.e. star fish, sea urchins, and sea lilies) found in almost all marine environments and often major components of seafloor communities. Originating in the early to middle Devonian, the group quickly diversified and is today the most species rich echinoderm clade. Unfortunately, our knowledge of their diversity and evolutionary pathways during the Late Paleozoic has been understudied leaving a large gap in our understanding of their true biodiversity. This can be attributed to study methods and a poor understanding of Paleozoic ophiuroid skeletal morphology. Ophiuroid skeletons are composed of thousands of individual calcite ossicles which easily disarticulate shortly after death, but individual ossicles can be found in high numbers in washed sediment. Taxonomic studies of Paleozoic ophiuroids have historically been focused on morphologies of the central-disk, with sparse attention being paid to the intricate morphology of the skeletal elements of the arm. Recent studies of Mesozoic and Cenozoic ophiuroids, however, have focused on the morphologies of skeletal elements of the arm called lateral arm plates which bear spine articulations. These plates are morphologically distinctive, numerous, and have proven to be diagnostic for taxonomic assignment. Here, we use similar methods established with studies on Mesozoic and Cenozoic ophiuroids to describe a Late Mississippian ophiuroid fauna from the Indian Springs Shale Member of the Big Clifty Formation in Sulphur, Indiana utilizing lateral arm plates collected from washed sediment. The goal of this study is to establish a framework for describing Paleozoic ophiuroids to fill in the gap of our knowledge of Late Paleozoic ophiuroid biodiversity. We find that this single locality has higher taxonomic diversity than previously described for Mississippian global diversity and has higher diversity than the most diverse locality known during this time period utilizing wholly articulated ophiuroid skeletons. In all, eleven taxa are described, with five new species and one new genus described, and four taxa with unknown affinities. Utilizing these methods, we can continue to investigate Late Paleozoic localities to get a better understanding of true Late Paleozoic ophiuroid biodiversity.