Great Basin Naturalist


The first reported mammal fossil from Dry Mesa Quarry (Upper Jurassic Morrison Formation, Mesa County, Colorado) is the distal end of a right humerus. It is very similar to humeri described by Jenkins (1973) from the Morrison Formation at Como Bluff, Wyoming. It has a distinct ulnar condyle and a spiral humero-ulnar joint, both features found in prototherian mammals but not in therians.