SANTONIAN MAMMALS FROM SOUTHERN UTAH AND IMPLICATIONS FOR THE AQUILAN LAND MAMMAL “AGE”

Mammals of Santonian age have been recovered from the John Henry Member of the Straight Cliffs Formation within the Grand Staircase-Escalante National Monument, southern Utah. The multituberculate fauna includes the oldest record of Mesodma, the Cimolomyidae is represented by a possible species of Cimolomys, Cimolodon foxi (formerly only known from the Judithian) is present along with other two other cimolodontids, and there are two species of Cedaromys. The therian fauna includes Potamotelses sp., Picopsis sp., Spalacotheridium sp. and the marsupials Varalphadon sp., Alphadon sp., and a stagodontid. The presence of Potamotelses and Picopsis, neither of which are known from the overlying lower Campanian Wahweap Formation, suggests closer affinities with the fauna of the Milk River Formation of Alberta, Canada, and may indicate that the Milk River fauna is of latest Santonian age rather than early Campanian. As the fauna from the Wahweap Formation is considered to be Aquilan, and the Aquilan Land Mammal “Age” is based on the fauna recovered from the upper part of the Milk River Formation, it is likely that the Aquilan spans at least some part of the Santonian through the early Campanian.