A new aetosaur, Tecovasuchus chatterjeei gen. et sp. nov., from the Upper Triassic (middle or upper Carnian) Tecovas Formation of Texas is described, based primarily on osteoderms from several individuals. The diagnosis is based on a unique suite of osteoderm characters: very wide dorsal paramedian osteoderms; a low, keel-shaped dorsal boss on the dorsal paramedians that does not reach the posterior margin of the osteoderm; a strut on the ventral surface of the dorsal paramedians; ornamentation on the dorsal paramedians with both deep pits and fainter radiating grooves; a unique strongly thickened and beveled posterior edge on the dorsal paramedians; a prominent raised anterior bar on both the dorsal paramedian and lateral osteoderms; lateral osteoderms with dorsoventrally flattened, posteriorly excavated horns, reduced, tongue-like dorsal flanges, and larger, plate-like ventrolateral flanges. The low number of diagnostic criteria for identifying aetosaur osteoderms results in mandatory splitting at the generic level. Some specimens of Tecovasuchus have been misidentified previously as Paratypothorax, suggesting that shoehorning osteoderms into previously recognized taxa may conceal greater taxonomic diversity among aetosaurs than has generally been appreciated. Specimens with multiple osteoderms assignable to a single individual are important in naming and characterizing new aetosaur taxa, and at least one complete osteoderm is usually necessary when assigning specimens to pre-existing taxa.