ABSTRACT The Morrison-Golden Fossil Areas National Natural Landmark, Colorado, USA, including Dinosaur Ridge, is rich in geological and paleontological history, ranking historically as the premier location and type area for Late Jurassic dinosaurs like Stegosaurus and Diplodocus . As the type area for the Morrison Formation, it famously became central in the “Bone Wars” underway in the 1870s. After a brief historical introduction at Stop 1, the trip will explore the ‘mid’-Cretaceous Dakota Sandstone (Stop 2), which yields the top-ranked dinosaur tracksite in the United States, with two type ichnospecies and the most accessible “nest scrape display trace” evidence of dinosaurian sexual display found anywhere. It also an important location for the study of microbial mat in association with dinosaur tracks, now photogrammetrically surveyed in detail. Dinosaur Ridge serves as the type area for the “Dinosaur Freeway” and the transgression of the Western Interior Seaway. Its diverse invertebrate traces have also been described in detail. After lunch at the Dinosaur Ridge Visitor’s Center exhibit (Stop 3), the trip will move a short distance to Golden to view the type localities for the first bird and crocodilian tracks ever reported from the Mesozoic (Stop 4). We will also visit the younger (Late Cretaceous) Laramie Formation, exposed in the Golden clay pits, cut by the Golden fault, and the source of historically famous paleofloras, the first known Ceratopsian tracks, and other type traces now developed as Triceratops Trail (Stop 5), constituting part of the well- documented Fossil Trace and School of Mines Geological Trail complex. The field excursion will involve easy walks and no strenuous climbs.

Abstract The Late Campanian-aged Kaiparowits Formation (72.5–76.6 Ma) is a thick, fossiliferous fluvio-overbank–lacustrine complex deposited in south-central Utah. Host to one of the richest, most diverse Campanian terrestrial fossil records in North America, the physical environment of the Kaiparowits ecosystem, particularly the dynamics of the hydrological 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. Isotopic compositions of serially sampled tooth enamel phosphate (δ 18 O p ) from tyrannosaur teeth were analysed to see if they held data that could clarify the palaeohydrology of the Kaiparowits Formation. To assess a greater palaeoecological context for the tyrannosaurs, the isotopic composition of their teeth was compared to other faunal elements, including the giant alligatoroid Deinosuchus , and turtles (Baenid, Gilmoremys , Neurankylus and Trionychid) from the same quarry. The δ 18 O w calculated from tyrannosaur was low, suggesting that isotopically-light, high-altitude runoff strongly influenced the local hydrology of the Kaiparowtis Formation. The seasonal change in δ 18 O of tyrannosaur drinking water ranged from −21.0 to −14.4‰ V-SMOW, while δ 18 O w calculated from turtles and crocodiles ranged between an average of −9.3 and −10.9‰, respectively. The seasonal precipitation pattern and temperature of the Kaiparowits Formation was then compared to analogue settings, such as the monsoonal climate of Hanoi, Vietnam and Cuiaba, Brazil. While similarities exist between these sites, the unique configuration of the Sevier Mountains adjacent to the nearby Western Interior Seaway provides the unique setting for a complex palaeohydrological system that results in a wide range of δ 18 O w as a result of cold seasonal precipitation at high elevation that runs off and mixes with local precipitation (−6.0 to −4.68‰) sourced from the Western Interior Seaway. This study demonstrates the importance of serial- and micro-sampling of multi-taxa comparisons for isotopic investigations of palaeohydrological systems.