COCHLIODONT SHARK TEETH FROM THE BIRD SPRING FORMATION (CARBONIFEROUS) OF SOUTHERN NEVADA

Cochliodonts were meter-size, shell-crushing sharks that lived in the late Paleozoic. They are known almost exclusively from their large, undulatory teeth. In North America, cochliodont teeth are relatively common in the carboniferous of the Midwest, and they have been reported as far west as Arizona. Here we report occurrences of cochliodont teeth in three separate locations in the Bird Spring Formation of the Spring Mountain Range of Southern Nevada. This is the first reported occurrence of these teeth in this area. Two of the samples are individual teeth from an unidentified genus. The third specimen is a complete mandible with six intact teeth belonging to the genus Deltodus. The Bird Spring Formation extends from late Mississippian into the Permian. The Deltodus jaw and one of the isolated teeth were recovered stratigraphically low within the Bird Spring Formation, so these teeth are probably early Pennsylvanian. The other isolated tooth was collected at a higher stratigraphic level, later in the Pennsylvanian. Further research is underway to more precisely determine the age of these teeth.

The lithologies of the shark-tooth bearing horizons are skeletal packstones and wackestones dominated by skeletal grains of crinoids and brachiopods. A lack of planer deposition and an abundance of disarticulated brachiopod valves indicates considerable turbulence. We conclude that these sediments accumulated above storm wave base. The Spring Mountains lay in equatorial latitudes during the Carboniferous. We conclude that the Bird Spring cochliodonts were living in an equatorial, open-marine setting in water depths no greater than around 30 meters. These shell-crushing sharks were probably feeding on brachiopods and crinoids that they scooped off the seafloor.