A Lateral Osteoderm From Kryphioparma Caerula (Pseudosuchia: Aetosauria) From the Upper Triassic (Norian) Chinle Formation of Arizona

Recent collecting of fossil vertebrates in the Chinle Formation at Petrified Forest National Park (PEFO) and reinvestigation of historic collections resulted in the recognition of a new aetosaurian taxon, Kryphioparma caerula. Although distinctive, K. caerula was initially described from several fragmentary paramedian osteoderms from PEFO and the nearby Placerias Quarry, however the anatomy of the lateral osteoderms remained unknown. Here, we refer an isolated lateral osteoderm from the Placerias Quarry to K. caerula based on an ornamentation composed of large elliptical-to-rounded pits on the dorsal surface that are randomly arranged, a prominent anterior bar, a strongly obtuse angle between two partially preserved flanges, an elongate lateral eminence (spine) with a strongly embayed posterior margin, and sharp anterior ridge. This combination of anatomical features of the isolated lateral osteoderm is clearly aetosaurian and differs in significant ways from the other known aetosaurian taxa from the site. A parsimony analysis recovers K. caerula nested within the inclusive clade Typothoracinae. This lateral osteoderm demonstrates that K. caerula was a spinose aetosaur, a bauplan observed in both typothoracine and desmatosuchin aetosaurians. Thus, further highlighting observed convergence between these groups and indicating a need for a reevaluation of lateral osteoderm characters used for phylogenetic analyses.