A Description of the New Hybodont Shark Genus, Columnaodus, from the Burlington and Keokuk Limestones (Carboniferous, Mississippian, Osagean) of Illinois and Iowa, USA

Bonebeds occurring in exposures of the Burlington and Keokuk Limestones (Mississippian/Osagean) along the Iowa and Illinois border (USA) contain an abundant and diverse collection of chondrichthyan remains that includes teeth, spines, denticles, and coprolites. These remains represent cochliodont, hybodont, petalodont, ctenacanthid, symmoriid, and acanthodian (stem chondrichthyan) taxa. The thickest of these beds, herein referred to as the Burlington–Keokuk bonebed, occurs at the top of the Burlington Limestone and presents a remarkable opportunity to study the assemblage of mid-continent, Middle Mississippian chondrichthyans. Bulk matrix samples of this bonebed were collected from two quarries (Biggsville Quarry, Biggsville, IL, USA, and Nelson Quarry, Mediapolis, IA, USA) and disaggregated. Among the multitude of previously known taxa, several teeth represented a new genus and species of hybodont shark. Herein, we describe these teeth as Columnaodus witzkei (gen. et sp. nov.), a hybodontiform with dental features comparable to unnamed specimens reported from elsewhere.