FOSSIL TRACKS IN THE JURASSIC AZTEC SANDSTONE OF RED ROCK CANYON NATIONAL CONSERVATION AREA, CLARK COUNTY, NEVADA

At the request of Red Rock Canyon National Conservation Area (RRCNCA) managers we have completed a systematic study of trace fossils in the Aztec Sandstone exposed within RRCNCA (on the west side of Las Vegas Valley), including photogrammetric documentation of the main tracksites. Prior to 2011 no tracksites were known to occur within RRCNCA. In that year, some Grallator (tridactyl theropod dinosaur tracks) undertracks were discovered by hikers and publicized in the local newspaper. This immediately led to the discovery of another Grallator site, which also includes an invertebrate trackway. In 2012, eight additional tracksites (including a variety of vertebrate and invertebrate traces) were discovered, mostly by hikers who were actively looking for tracks. Four additional sites were discovered in 2015.

We have now documented a total of fifteen trace fossil sites to occur within RRCNCA, and we have no doubt that more sites will be found in future years. Seven ichnotaxa occur at these fifteen sites. Three of these are vertebrate ichnotaxa: Grallator, Brasilichnium, and Ichnotaxon A (a previously undescribed track type). The remaining four invertebrate taxa include Entradaichnus, Octopodichnus, Paleohelcura, and Planolites; all four of these were probably produced by arthropods. All of these ichnotaxa except Ichnotaxon A have also been reported from the Navajo and/or Nugget sandstones (correlative units in Utah and adjacent states). Four of the RRCNCA sites contain multiple ichnotaxa.

A key aspect of this study has been photogrammetry, which involves the use of overlapping photographs and special software to produce 3-dimensional digital models of tracksites. Such models can be used for research, interpretive displays, and also for monitoring the natural weathering or vandalism of a tracksite.

Our future research will involve a comparison of the RRCNCA tracksites with those in other areas where the Aztec Sandstone is exposed, as well as with the Navajo and Nugget sandstones.