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.
Prothero, Donald R. and Jensen, James A.
"A mammalian humerus from the Upper Jurassic of Colorado,"
Great Basin Naturalist: Vol. 43
, Article 3.
Available at: https://scholarsarchive.byu.edu/gbn/vol43/iss4/3