Geologic setting of a new Paleocene mammal locality in the northern Powder River Basin, Montana ( USA).

The fossil-bearing unit is at approximately the same stratigraphic horizon as the lowest coal bed in the Tongue River Member of the Fort Union Formations. The fossils occur approx 50m above the base of the Tongue River Member in a 0.6m thick, yellowish-gray, sandy conglomerate that is interpreted to be a fluvial channel-lag deposit. The fauna includes fossils of fish, turtles, crocodiles, and mammals. Mammals thus far recovered include 21 species distributed between 17 families. Genera known from rocks of both the Torrejonian and the Tiffanian land mammal ages (middle and late Paleocene) are present, but the evolutionary stage of Aphronorus and the mutual presence of Nannodectes and a primitive species of Ectocion suggest a Tiffanian (late Paleocene) age for the deposit.-from Authors