THE NOVEL OCCURRENCE OF A LINTEL STONE CONTAINING VERTEBRATE ICHNOFOSSILS IN A PUEBLO III STRUCTURE IN UTAH

The Early Jurassic Navajo Sandstone is a vast eolian deposit that represents the largest erg to have existed on Earth. Exposed throughout southern Utah, the Navajo Sandstone contains localized, water-lain interdune deposits consisting of impermeable, fine-grained sediments. Through both trace and body fossil evidence, these interdunal “lakes" are known to have supported a relatively diverse biota, and are increasingly the subject of paleontological studies. Additionally, these impermeable interdune deposits are studied by geomorphologists for their role in groundwater sapping and the creation of alcoves and box canyons within the Navajo Sandstone.

The ruins of a Pueblo III period structure with some Basketmaker II/III components is located in a small, multi-component cliff dwelling in a Navajo Sandstone alcove located on Bureau of Land Management land in San Juan County, Utah. These ruins indicate the structure was constructed almost entirely of rectangular blocks of creme-colored eolian Navajo Sandstone, except for a single slab of flat, pinkish, fluvial sandstone which serves as the lintel over the struture entrance; the lintel likely originated in either the Late Triassic Chinle Formation or the Early Jurassic Kayenta Formation (although other formations remain a possibility), which are both fluvial and are both located nearby (within walking distance). The lentil is also unique in that it bears a fossilized dinosaur track, facing down into the constructed passageway. The track is preserved in convex hyporelief and is identified as Grallator isp., made by a relatively small, three-toed, theropod dinosaur. This track type is well-documented in southern Utah where the Navajo Sandstone, Chinle Formation, and Kayenta Formation are exposed.

As the Chinle and Kayenta Formations are not immediately adjacent to this cliff-dwelling, and the Navajo Sandstone does not contain fluvial beds of this nature nearby, the slab with the fossilized track appears to have been transported here from another location and then deliberately placed as the lintel in this structure by the builders. The practice of incorporating vertebrate ichnofossils into cliff-dwelling structures, Pueblo III or otherwise, in the American southwest is heretofore unknown and this discovery is the first such documented occurrence.