IMPROVING OUR UNDERSTANDING OF LATE PALEOZOIC BRITTLE STAR DIVERSITY: A NEW BRITTLE STAR FAUNA FROM THE INDIAN SPRINGS SHALE MEMBER OF THE BIG CLIFTY FORMATION, SULPHUR, IN

Brittle stars, echinoderms with a large central disk and long, slender arms, are the most species-rich class of modern echinoderms. However, our current understanding of brittle star diversity during the Paleozoic presently does not show a similar pattern. Until recently, the known record of this group has been limited because of outdated study methods that focused on descriptions of fully articulated skeletons, biasing the record towards localities that preserve pristine, articulated skeletons. Here, we use a new method centered on the identification of dissociated skeletal elements of the arm, called lateral arm plates (LAPs), to describe a new fauna of Late Paleozoic brittle stars from the late Mississippian (Chesterian; Serpukhovian) and discuss its implications for a more robust picture of Late Paleozoic brittle star diversity.

Friable shale was collected from the Indian Springs Shale Mb. of the Big Clifty Fm. (Upper Mississippian) in Sulphur, IN. Sediment was boiled overnight in a hydrogen peroxide bath to separate rock from fossil material. LAPs were picked by hand from sieved fossil residues and photographed using a scanning electron microscope. Lateral arm plates were compared to descriptions of known articulated brittle stars when possible. This method allows us to identify and characterize numerous taxa even though articulated specimens were not preserved at the locality.

In total, fourteen brittle stars species were identified including one stenuroid, two protasterids, one cheiropterasterid, three furcasterids, one Cholaster-like taxon, one Aganaster-like taxon, and five new species of unknown affinities. This new fauna expands the stratigraphic range of several brittle star taxa into the Upper Mississippian. This includes stenuroids which became almost entirely extinct by the end of the Devonian. In addition, this fauna is one of the most species rich brittle star faunas known from the Paleozoic and is twice as diverse as the most speciose Mississippian fauna based on fully articulated specimens. This study shows that to understand the diversity of Paleozoic brittle stars, the focus must include the collection and description of disarticulated skeletal elements at pivotal times in Earth’s history.