ADDITIONAL VERTEBRATES FROM THE CARBONIFEROUS BURLINGTON-KEOKUK BONE BED OF THE ILLINOIS BASIN

The regionally continuous bone bed at the boundary between the Burlington and Keokuk Formations (Carboniferous: Viséan, 346.7-330.9 Ma) has been known to the paleontological community for nearly 150 years and contains a large assemblage of fossil fishes and Chondrichthyans. Given the multitude of fossils, many more species are likely present than currently known. Samples recently collected from the Nelson Quarry (Des Moines County, Iowa) report Acanthodians (Ishnacanthiformes indet.) and numerous Chondrichthyans such as Holocephalians (Stethacanthus sp., Deltodus undulates, and Venustodus sp.) and primitive Elasmobranchs (Orodus daedalus, Saivodus striatus, and Protacrodus sp.) as well as a diverse group of Petalodontiform sharks: Antilodus sp., Chomatodus sp., Petalodus sp., and Polyrhizodus sp. We collected samples from this horizon at two other quarries (Mediapolis, IA and Biggsville, IL) for acid dissolution and report six taxa that were absent from the quarry in Des Moines County. Our understanding of Phoebodontiform shark diversity from this region has increased with the report of Thrinacodus nanus. The diversity of the genus Orodus has also increased with our discovery of “O.” catanaus (the taxonomy of this species is uncertain) and O. vericostatus. We also report material belonging to bony fishes (Paleonisciformes indet.) as well as unknown Hybodontiform teeth and the large durophagous Chondrichthyan Deltodus grandis. Overall, this means that every major group of vertebrates known from this layer (Chondrichthyans and Osteichthyans) is much more diverse than previously thought.