Abstract

The Red Peak Formation includes a large part of Wyoming's thick sequence of Triassic red beds. The perplexing dearth of fossils in this extensively exposed unit has handicapped determination of its depositional environment. A new interpretation of distinctive sole marks from the formation provides a glimpse of vertebrate activity at three localities in west-central and southeastern Wyoming. At each locality, the basal surface of a fine-grained sandstone exhibits subparallel, striated ridges, each several centimeters long and one to two centimeters in relief. Both projections and reflexures define a consistent polarity for the ridges at any one locality. This unique hypichnial relief was formerly interpreted as casts of prod marks made by driftwood. The striated ridges are now known to be very similar to distinctively clustered and spaced sole traces in the correlative Moenkopi Formation of southern Utah. The Utah features have been interpreted (Webb, 1980) as marks made by an amphibious tetrapod pushing along a river bottom with the tips of its toes. Although the best exposed Red Peak surfaces have the sole marks so crowded that neither digit spacing nor individual footfalls can be discerned, similarities between individual ridges at the Utah and Wyoming localities indicate a genetic relationship.--Modified journal abstract.

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