Upper Jurassic dinosaur bonebeds at Ten Sleep, Wyoming: stratigraphy, preliminary results and field reports of 2016 and 2017

The Upper Jurassic Morrison Formation that outcrops throughout the Western Interior of the United States is well known for its diverse environments and for its vertebrate, invertebrate and floral biodiversity, in great part fueled by the numerous paleontological expeditions focused on extensive fossil record of the formation’s dinosaurian fauna, since late 19th century. In 2014, plans started to be made for a new expedition into the Morrison Fm. outcrops close to the town of Ten Sleep, where digs have been carried out in private land since 2006. This expedition represented the return of the American Museum of Natural History (AMNH) to the Big Horn Basin since Barnum Brown’s Howe Ranch expedition in the early 1930s, however this time, work would be under taken in public land. As such, a project was submitted to the Bureau of Land Management in order to obtain permission to dig and survey two distinct localities between the towns of Ten Sleep and Hyattville: Cosm and Dana quarries. The expedition counted with elements from AMNH and Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa (FCT-UNL), and was carried out between the months of August and September, of 2016 and 2017. At the end of two years, the yellowish to tan massive cross bedded sandstones that outcrop along the hills of the Ten Sleep-Hyattville area, have proven to rich fossiliferous riverbank deposits, both in quantity and diversity, mainly preserving dinosaurian remains (some preserving cranial elements) representative of the upper levels of the Morrison Fm. such as Allosaurus sp., Apatosaurus sp., Camarasaurus sp., and unidentified diplodocids, ornithopods, and stegosaurid. This information, along newer stratigraphical data for the area, and the detailed description of the digging season, are here reported as to record the first steps taken in what is to be a long term project