Proceedings of the South Dakota Academy of Science,Vol. 76 (1997) 275 FOSSIL VERTEBRATES OF THE NIOBRARA FORMATION IN SOUTH DAKOTA James E. Martin and Bruce A. Schumacher Museum of Geology SD School of Mines & Technology Rapid City, SD 57701 David C. Parris and Barbara Smith Grandstaff Bureau of Natural History New Jersey State Museum Trenton, NJ 08625 ABSTRACT The Niobrara Formation through the mid-continent has been classically known for its assemblage of fossil fish, birds, and reptiles. Within this area, the Niobrara chalk of South Dakota has received relatively little attention. Only a few fish, a mosasaur, and a plesiosaur have been described from this marine formation heretofore. With additional investigations by the authors, the known vertebrate assemblage from South Dakota now includes: Squalicorax falcatus, Squalicorax kaupi, Cretoxyrhina mantelli, Echinorhynus, Ptychodus mortoni, Pachyrhizodus caninus, Pachyrhizodus minimus, Protosphyraena gladius, Protosphyraena nitida, cf. Apateodus, Ichthyodectes ctenodon, Xiphactinus audux, Bananogmius evolutus, Cimolichthys nepaholica, Stratodus apicalis, Saurodon leanus, Saurocephalus lanciformis, Enchodus shumardi, Enchodus petrosus, Enchodus gladiolus, cf. Lophochelys, Toxochelyidae, Polycotylus latip- innus, Pteranodon, Clidastes propython, Platecarpus tympaniticus, Tylosaurus proriger, cf. Ichthyomis, and Hesperomis regalis. Most of these taxa represent new records from the Niobrara Formation of South Dakota and attribute an ear- ly Coniacian to early Campanian age to the unit. The type specimens of Enchodus shumardi Leidy 1856 and Cladocyclus occidentalis Leidy 1856 (a taxon based upon fish scales which are most likely those of Ichthyodectes ctenodon) are from the Niobrara Formation of South Dakota and may have been collected from deposits near the Cheyenne River..