ENIGMATIC, LARGE- AND MEGA-DIAMETER BURROWS IN THE LOWER PERMIAN CEDAR MESA SANDSTONE, COMB RIDGE AND MOQUI DUGWAY, SOUTHEASTERN UTAH

Preliminary fieldwork in the lower part of the Cedar Mesa Sandstone has found enigmatic large- and mega-diameter, subhorizontal burrows in the southern part of Comb Ridge and the Valley of the Gods. Large-diameter burrows in the southern part of Comb Ridge occur in interbedded sandstone, siltstone, mudstone, and gypsum beds, but prominently found in pedogenically modified clastic interbeds. Overall, the architectural morphology of the burrows is simple. Burrows are subhorizontal and at ~10–15 degrees from horizontal. The longest exposed burrow is nearly 50 cm. Burrow shape is elliptical and ~5–15 cm in diameter and ~2.5–5 cm in height, with the majority larger in diameter, rather than smaller. The surficial morphology preserved on the burrow walls is mostly smooth, however, the best-preserved burrows contain nearly 1-cm-diameter knobby surfaces, and scratch marks that are longitudinal to the burrow wall, as well curvilinear as C-shaped scalloped marks. Mega-diameter burrows discovered to date in outcrops above the Valley of the Gods vary from simple to moderately complex in architectural morphology, as simple branched networks rather than three-dimensional boxwork. The longest exposed burrow is nearly 150 cm. Burrows are strongly subhorizontal and at ~5–10 degrees from horizontal, with a short, J-shaped entrance. Burrow shape is strongly elliptical. Burrow diameter ranges from ~25–50 cm in diameter and ~5–10 cm in height; these dimensions likely indicate that the original diameter was also strongly elliptical. The surficial morphology preserved on the burrow walls varies from smooth to finely knobby and hummocky surfaces. Both sizes of burrows are interpreted to have been constructed by vertebrates of different sizes and likely from different families or orders. Squamate reptiles likely constructed the large-diameter burrows, whereas the mega-diameter burrows where likely excavated by very large reptiles or possibly by large labyrinthodont amphibians.