Santonian (late Cretaceous) mammals from the John Henry Member of the Straight Cliffs Formation, Grand Staircase-Escalante National Monument, Utah

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Abstract
The first North American mammals of definite Santonian age are described from the John Henry Member of the Straight Cliffs Formation of the Grand Staircase-Escalante National Monument of southern Utah. The fauna includes the oldest documented record of the multituberculates Mesodma (Mesodma sp., cf. M. minor and Mesodma sp.), the Cimolomyidae (?Cimolomys sp.), the tribotheres Potamotelses sp., Picopsis sp., and the marsupial Varalphadon sp. Also present in the fauna is the multituberculate Cimolodon foxi (formerly only known from the Judithian), other cimolodontids (Cimolodon spp., ?Cimolodon sp.), Cedaromys sp., cf. C. hutchisoni, Cedaromys sp., the symmetrodont Spalacotheridium sp., and the marsupials Alphadon sp., cf. A. halleyi, and a stagodontid(?). The fauna has close 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.