BIOSTRATIGRAPHIC UTILITY OF SANTONIAN-CAMPANIAN (LATE CRETACEOUS) NONMARINE RAY (RHINOBATOIDEA) TEETH, SOUTHERN UTAH

The Upper Cretaceous Santonian through Campanian nonmarine strata of southern Utah contain isolated teeth of Myledaphus sp., Myledaphus bipartitus, and several unnamed form genera and species of the Rhinobatoidea. Although these teeth are of limited value in rhinobatoid systematics, they may be of utility in biostratigraphic and paleoenvironmental studies. Myledaphus sp. first appears near the base of the John Henry Member (Santonian or Coniacian) of the Straight Cliffs Formation. The record of Myledaphus bipartitus is older than previously reported, as it has been recovered from the upper part of the John Henry Member (Santonian) approximately 100 m below the Wahweap Formation. Myledaphus appears to be absent in the overlying Wahweap Formation (early Campanian), but reappears in the younger the Kaiparowits Formation (late Campanian). The oldest record of the unnamed form genera A and B were recovered within the lower Santonian (or Coniacian?) of the John Henry Member of the Straight Cliffs Formation approximately 25 m above the Smokey Hollow - John Henry Member contact. Unnamed form genus C first appears in the Wahweap Formation. Further analysis may yet reveal more diversity. As Myledaphus rarely occurs in the same locality as the other unnamed taxa, some environmental factor may be controlling their distribution.