A new aetosaur (Archosauria: Pseudosuchia) from the upper Blue Mesa Member (Adamanian: Early–Mid Norian) of the Late Triassic Chinle Formation, northern Arizona, USA, and a review of the paratypothoracin <i>Tecovasuchus</i> across the southwestern USA

The Late Triassic Chinle Formation in northern Arizona and Dockum Group in northwestern Texas preserve a high aetosaur biodiversity within the Adamanian teilzone, including Desmatosuchus spurensis, Desmatosuchus smalli, Calyptosuchus wellesi, Adamanasuchus eisenhardtae, Typothorax coccinarum, Paratypothorax sp., Tecovasuchus chatterjeei, and Sierritasuchus macalpini. Here, we present a new aetosaur Kryphioparma caerula gen. et sp. nov. from the upper Blue Mesa Member of the Chinle Formation, Adamanian teilzone, in northern Arizona. Kryphioparma caerula sp. nov. is documented based on several isolated osteoderms collected from the Placerias Quarry and Petrified Forest National Park. Although fragmentary, it is evident that the paramedian osteoderms of Kr. caerula exhibit a dorsal ornamentation composed of large, randomly oriented oblong pits; a low concentration of pits relative to available surface area; well-developed anterior bar; a probable high width-to-length ratio; dorsoventrally thickened; well-developed ventral strut; and grooves along the posterior margin. This suite of morphological characters indicates that Kr. caerula is a typothoracine similar to Ty. coccinarum, Te. chatterjeei, and P. andressorum; its stratigraphic occurrence within the upper Blue Mesa Member makes it the oldest documented typothoracine to date. The documentation of Kr. caerula within the Placerias Quarry brings to question the taxonomic affinities of paratypothoracin material identified as “Tecovasuchus” by previous authors, as well as the biostratigraphic utility of Te. chatterjeei across the southwestern United States. We present the first unambiguous material referable to Te. chatterjeei from the Downs Quarry and Petrified Forest National Park. The documentation of Te. chatterjeei in the Chinle Formation of northern Arizona and Tecovas Formation of northwestern Texas suggests that this taxon may be biostratigraphically informative as it is currently constrained to strata within the Adamanian teilzone similar to Desmatosuchus and Ca. wellesi.