The first dinosaur postcranial body fossils from the Lower Jurassic Kayenta Formation of Utah

Abstract

The vertebrate assemblage of the Lower Jurassic Kayenta Formation is known for its preservation of post-end Triassic mass extinction lineages, including lissamphibians, lepidosaurs, turtles, mammaliamorphs, crocodylomorphs, pterosaurs, and ornithischian, theropod, and sauropodomorph dinosaurs. Most of the body fossils from the formation are known from its ‘silty facies’ in north-central Arizona and southwestern Utah, whereas the sandier ‘typical facies’ of northeastern Arizona preserves few body fossils, and until recently they were completely absent in the typical facies of southeastern Utah. A 2011 team conducting a paleontological survey of Arches National Park discovered the first body fossils from the typical facies of the Kayenta Formation in Utah, here identified as belonging to a single individual of a saurischian dinosaur, likely a theropod. The fossil elements include a partial centrum articular face, a prezygapophysis, part of a caudal vertebra, the distal end of a left radius, part of the distal end of a left femur, a shaft fragment from the left fibula, the distal end of right metatarsal I, and the proximal portion of left metatarsals III and IV. This specimen from Arches National Park underscores the importance of federally protected land in fossil resource management and suggests that the typical facies of the Kayenta Formation may be undersampled and could preserve more vertebrate bones than previously thought.