PALEOCLIMATIC IMPLICATION OF LOWER-MIDDLE UNIT OF THE KAIPAROWITS FORMATION USING THEROPOD TEETH FROM THE RAINBOW AND UNICORN QUARRY FROM THE GRAND STAIRCASE-ESCALANTE NATIONAL MONUMENT

The Late Campanian age Kaiparowits Formation (74-76.5 Ma) is a thick, fossiliferous fluvio-overbank-lacustrine complex deposited in south-central Utah. Despite its rich fossil record, the physical environment of the Kaiparowits ecosystem, particularly the dynamics of the hydrologic system, remains obscure. In 2014, an extensive bonebed was found in a conglomeratic sandstone unit of fluvial origin, known as the Rainbows and Unicorns quarry. The quarry has yielded a diverse fossil assemblage that includes gar and amiid fish, a variety of turtles, a giant alligatoroid (Deinosuchus), and multiple individuals of tyrannosaurid. Because tyrannosaurs frequently shed teeth, one tooth could potentially record short term changes in water sources. Additionally, their large tooth size allows for higher frequency sampling. Thus, isotopic compositions of serially sampled tooth enamel phosphate (δ¹⁸O_p) from tyrannosaur teeth were analyzed to see if they provide data that could clarify the paleohydrology of the Kaiparowits Formation. The mean δ¹⁸O_p value of the tyrannosaur teeth was 13.14‰ VSMOW, and the δ¹⁸O_p value ranges from 10.23 to 14.81‰ VSMOW in a single tooth. Assuming the dinosaur body temperature is comparable to the modern bird (37°C) and relative humidity is 70%, the δ¹⁸O of ingested water ranges from -20.96 to -14.41‰ VSMOW. In contrast, the δ¹⁸O value of pedogenic carbonate from the quarry ranges from 22.83 to 24.05‰ VSMOW, and δ¹⁸O value of meteoric water estimated using these values ranges from -7.79 to -6.11‰ VSMOW. This suggests a strong seasonal variability in the water δ¹⁸O composition, which is not discernible on pedogenic carbonate isotopic composition.