USING SEQUENCE STRATIGRAPHY TO PREDICT VERTEBRATE TRACKWAYS IN COASTAL SETTINGS: JURASSIC GYPSUM SPRING AND SUNDANCE FORMATIONS, BIGHORN BASIN, USA

Recent advances in sequence stratigraphy have made it an effective tool for understanding the occurrence of marine invertebrate and vertebrate fossils; here, we test its utility in predicting the occurrence of terrestrial vertebrate trackways. Our test was performed in the Jurassic Gypsum Spring and Sundance Formations of Wyoming, where the sequence-stratigraphic and facies framework is well known. The senior author discovered 267 new vertebrate tracks in these strata, all at horizons hypothesized to harbor potential tracks. 90 tracks from swimming terrestrial reptiles were found in the middle limestone-rich member of the Gypsum Spring Formation at one locality on Sykes Mountain. These are preserved as two or three parallel scratches ranging from 2.8–17.3 cm in length. Though similar swim tracks have been reported in this unit, they have not been reported at Sykes Mountain. 175 narrow-toed tridactyl theropod tracks were found at 3 Canyon Springs Formation localities near the Red Gulch Dinosaur Tracksite (RGDT) and the Yellow Brick Road Dinosaur Tracksite (YBRDT). These tracks have lengths ranging from 2.4–16.4 cm. In addition, 1 unidentified wide-toed track was found near a theropod trackway in the Canyon Springs Formation. Another enigmatic wide-toed track was observed in the Canyon Springs Formation on Sheep Mountain. In the Windy Hill Sandstone at Sykes Mountain, an unidentified track was found. All trackway localities display rippled, microbial surfaces, suggesting that microbial mats are responsible for track preservation. Trackway discoveries in the Gypsum Spring and Sundance Formations demonstrate the utility of sequence stratigraphy for discovering potential trackways. Theropod tracks near the RGDT and the YBRDT add to previous studies in this area, while new swim tracks on Sykes Mountain emphasize sequence stratigraphy’s usefulness for identifying new potential trackway horizons, as well as settings where microbial preservation of tracks is favored.