NEW TRIASSIC VERTEBRATE TRACKS FROM THE MOENKOPI FORMATION OF LAKE MEAD NATIONAL RECREATION AREA: A RECORD OF THE OLDEST MESOZOIC TRACKS FROM THE STATE OF NEVADA
The traces are found along bedding planes in epirelief. The host sediment is dark brown, very fine-grained sandstone to siltstone with symmetrical ripple marks. Traces are shallow in relief with a least one track-maker being quadradactyl. Some shallow claw impressions are reminiscent of swimming tracks from Triassic units in neighboring Utah.
By measuring a detailed stratigraphic section of the Moenkopi Formation throughout the area, combined with sedimentological data, we conclude that the tracks were produced in a tidal flat depositional paleoenvironment. Interbedded with the ripples, trace fossil-bearing beds are finely-laminated mudrocks more indicative of subtidal deposition. Photogrammetry will be used to digitally model the tracks in three dimensions. The models can reveal details of the fossils not apparent to the naked eye. Due to the partial preservation of tracks from this site, ichnotaxonomic identifications cannot be made, nor potential track-makers, at this time. However, these tracks do represent the oldest Mesozoic vertebrate traces from Nevada, and some of the western-most terrestrial Triassic traces in North America expanding the record of Moenkopi ecosystems further afield. Further work in the region will likely reveal additional tracks making identifications possible.