FIRST REPORT OF CHELICHNUS GIGAS IN THE LOWER PERMIAN (WOLFCAMP) QUEANTOWEAP SANDSTONE OF SOUTHERN NEVADA

We report the discovery of a tetrapod trackway in the Lower Permian (Wolfcampian) Queantoweap Sandstone in the Gold Butte area of Clark County, Nevada. The Queantoweap Sandstone is correlative with the Esplanade Sandstone (uppermost formation of the Supai Group) of Grand Canyon. The preserved trackway consists of six strides, with an average stride length of about 15 cm and a trackway width that varies from 17 to 18 cm. Pes lengths are about 9.5 cm, and the pace angulation is 80˚. Three distinct, forward-directed digits are present on the pes prints, which overprint and obscure the details of the manus tracks. Pes sole impressions are round. We tentatively assign this trackway to Chelichnus gigas.

Chelichnus trackways are very common in the Coconino Sandstone (Leonardian) of the Grand Canyon region, but they have not previously been reported from the older Esplanade Sandstone or the correlative Queantoweap Sandstone. Also, most Chelichnus tracks in the Coconino are much smaller than the tracks reported here. The occurrence of this trackway extends the range of C. gigas downward into the Wolfcampian. The Queantoweap trackway is similar in size and morphology to a trackway reported in the 1980s in the uppermost Wescogame Formation of Grand Canyon, which suggest that the range of this ichnospecies extends into the uppermost Carboniferous (Virgilian). 

Chelichnus is commonly interpreted to occur in eolian deposits. However, the Queantoweap Sandstone section examined in this study consists of tidally-dominated and storm-dominated facies. The fossil trackway occurs near the top of the formation within a ripple-marked bed that we interpret to represent a ripple-marked tidal flat. We therefore conclude that the Chelichnus gigas trackmaker lived at least part of the time in a shallow marine environment.