Aetosaurus from the Upper Triassic Bull Canyon Formation, Quay County, New Mexico, and its significance

Aetosaurus is an Upper Triassic genus of relatively small and inornate aetosaurs known from three species: A. ferratus, A. crassicauda, and A. arcuatus. A record of A. arcuatus from the Bull Canyon Formation of the Chinle Group in east-central New Mexico correlates these strata to Aetosaurus-bearing strata in the eastern United States, Italy, Greenland, and Germany. The genus has been stated to be a reliable tetrapod index fossil for the Revueltian (Norian), making the specimens of A. arcuatus from the Bull Canyon Formation in Quay County, New Mexico, which are part of the characteristic Revueltian tetrapod assemblage, important to Late Triassic tetrapod biochronology. While many specimens have been collected from the Aetosaurus locality in the Bull Canyon Formation (NMMNH L-501), only the most diagnostic have been previously reported. Here we describe additional aetosaurian material in the collection of the New Mexico Museum of Natural History from L-501, including a partial skeleton, numerous paramedian and lateral scutes, lateral appendage scutes, vertebral fragments, and various limb and hip elements. After Typothorax, Aetosaurus is the second most common aetosaur in the Bull Canyon Formation. The distribution of Aetosaurus in Chinle Group strata includes records in the Rock Point Formation, well documented from the Eagle basin of Colorado. These records indicate that the Revueltian-Apachean boundary is not, as previously assumed, coincident with the base of the Rock Point lithosome, but instead is at least locally above its base.