Underprints of vertebrate and invertebrate trackways in the Permian Coconino Sandstone in Arizona

The only fossils in the Permian Coconino Sandstone of northern Arizona are abundant fossil trackways. A slab of Coconino Sandstone contains underpants of both vertebrate and invertebrate animals, exposed at two levels separated by a 1-2 mm layer of sand. The underprints on the lower level are deeper and much more distinct than the same trackway exposed on the higher level. The tracks on the upper level were partly infilled by the fine sand, which does not contain clays or other material that could provide cohesiveness. The trackways on this upper level also appear to be underprints, but formed closer to the surface. Many other fossil trackways in the Coconino Sandstone are probably also underprints, since they closely resemble the documented underprints. The mechanics of underprint formation may also explain the origin of some tracks that are very deep, with steep sides that even overhang the front of the track.