Stagonolepis, AGASSIZ, 1844

Sulej, Tomasz, 2010, The skull of an early Late Triassic aetosaur and the evolution of the stagonolepidid archosaurian reptiles, Zoological Journal of the Linnean Society 158 (4), pp. 860-881 : 878-879

GENUS STAGONOLEPIS AGASSIZ, 1844

Diagnosis: Stagonolepis differs from Longosuchus and Desmatosuchus in the possession of premaxillary teeth, and the absence of strongly curved dorsolateral osteoderms with spines. Stagonolepis differs from Longosuchus and Desmatosuchus in the possession of a narrow contact between the parietal and postorbital. Stagonolepis differs from Desmatosuchus in the possession of the following characters: the prominent rough projection on the articular; the foramen incisivum and the frontal being proportionally longer. Stagonolepis differs from Aetosaurus by the possession of the following characters: a parietal that is narrower than the frontal; a parietal that is proportionally short; an enlarged supratemporal fenestra; a more ventral position for the postorbital/squamosal contact; five rather than four teeth in the premaxilla; 11–12 rather than nine to ten teeth in the maxilla; seven to ten rather than seven to eight teeth in the dentary; bosses present on the paramedial scutes rather than ridges; belly scutes wider than longer. Stagonolepis differs from Coahomasuchus and Redondasuchus in possessing paramedial scutes with radial sculpture. Stagonolepis differs from Typothorax , Paratypothorax , and Tecovasuchus in possessing narrow paramedian dermal plates. Stagonolepis differs from Neoaetosauroides by the possession of the following characters: long posterior process of premaxilla; 11–12 rather than eight teeth in the maxilla; seven to ten teeth rather than seven teeth in the dentary; choana larger than suborbital fenestra (in Neoaetosauroides they are of similar size). Stagonolepis differs from Aetosaurus and Neoaetosauroides in the possession of the following characters: a more strongly convex ventral margin of the maxilla; the anterior end of the maxilla positioned posterior to the midpoint of the naris (in Aetosaurus and Neoaetosauroides the anterior end of the maxilla is positioned anterior to the midpoint of the naris); a shorter edentulous region on the premaxilla.

Remarks: Several differences between Stagonolepis and Aetosaurus were observed by Walker (1961), but some of these proposed differences are questionable. Walker (1961) proposed that the nasal–frontal suture is posteriorly inclined away from the midline in Aetosaurus , but anteriorly inclined in Stagonolepis ; however, this character is variable amongst aetosaurs. The lateral groove on the frontal is similar in both genera The transverse ridge situated on the parietal anterior to the tuberculum is proportionally larger in Aetosaurus , but this could be size-related. The dental morphology is highly similar in both taxa. The lack of teeth in the premaxilla for Desmatosuchus was used in its diagnosis by Long & Murry (1995).