A New Triassic Bonebed from the Bears Ears Region of Utah

Poster presented at WAVP 2017. Abstract is as follows:<br>In the summer of 2016, field crews from the Museums of Western Colorado: Dinosaur Journey discovered a bonebed of large-bodied archosaurs in the vicinity of Fry Canyon, San Juan County, Utah. Nicknamed “Portal to NeCrocPolis” (P2N), the site preserves at least three armored archosaurs in brown mudstone with fine, <2cm thick white sandstones. The bonebed extends over 64 m in a NNE by SSW exposure and appears to be present across a draw, 80 m to the east, though colluvial deposits currently prevent precise correlation. The fossil-bearing deposit is situated approximately nine meters above a large, grayish-white channel sandstone that locally marks the boundary between the underlying Monitor Butte Member and the Church Rock Member of the Chinle Formation. The mudstone/sandstone beds are laterally extensive within the lower Church Rock Member within the Fry Canyon-Red Canyon area, though additional extensive fossil deposits like P2N have not been discovered. We interpret the bonebed to be monotaxic based on the presence of one articulated individual discovered during the initial survey. Surface-collected elements with morphology matching that of the in situ material have been recovered site-wide. Elements from all portions of the skeleton of the P2N animal have been recovered, and the in situ specimen preserves nine dorsal vertebrae, a partial pelvis, left and right thoracic ribs, and gastralia. Additional material from the cranium, lower jaw, cervical, dorsal, and caudal vertebral series, limbs (including phalanges and unguals), and dermal armor have been recovered. While the taxa bears some resemblance to both phytosaurs and aetosaurs, several characters seem to be ambiguous. Unique characters include dorsoventrally flattened, spade-shaped unguals, osteoderms with a distinct lateral bend and anterior articular surface, and teeth with higher-than-normal serration densities (5-6/mm vs. 1-2/mm in phytosaurs). This bonebed likely represents an accumulation of a poposaurid taxon from the Bears Ears region; additional fieldwork in 2017 is planned in order to fully excavate the site.<br>