BURROWS DUG BY LARGE VERTEBRATES INTO RAIN-MOISTENED, MIDDLE JURASSIC SAND DUNES

In south-central Utah, eolian cross-strata of the Escalante Member of the Entrada Sandstone contain inclined, cylindrical burrows up to 63 cm in diameter and 305 cm long. Twelve of the 14 large tunnels located during this study descend from 2nd and 3rd order bounding surfaces that formed on the lee slopes of large dune ridges, well above the water table. The tunnels are inclined 15-22 degrees; one tunnel ends in an expanded chamber. Eolian cross-strata fill proximal portions of four of the tunnels, and indicate that after abandonment, sand drifts migrated as much as a meter into the open shafts. Structureless sand and breccia blocks that were generated by roof collapse fill other tunnels. Animals dug the tunnels in rain-moistened, cohesive sand. The burrows may have served as temporary shelters from severe diurnal conditions in the shadeless, subtropical Entrada dune field.