VERTEBRATE BURROWS IN SANDSTONES OF THE LOWER JURASSIC GLEN CANYON GROUP IN THE VICINITY OF DINOSAUR NATIONAL MONUMENT, UTAH

We report the discovery of large burrows (about 20cm diameter), probably attributable to vertebrates, in sandstones of the Lower Jurassic Glen Canyon Group in the vicinity of Dinosaur National Monument, Utah. The burrows occur within a limited area in cross section on the exposure surfaces of the rock. The burrows are within the upper part of the Glen Canyon Group which is dominated by eolian dune sands. They occur within about a 2 meter interval of sandstone above a thin, discontinuous carbonate. Some of the burrows are truncated by an erosion surface at the top of this interval that is overlain by eolian sands.

There are gently curved, filled burrow segments up to a meter or more long, and there are some more extensive, branched burrows that are unfilled and supported by heavy iron oxide cement that lines the burrows. The burrows appear to be slightly slightly flattened ovals in cross section, wider than they are high. Their relatively large size and their irregular shape suggest that the burrows were made by vertebrates. Synapsids, including early mammals, are possible candidates, but dinosaurs cannot be ruled out.