Article: Aetosaurus (Archosauromorpha) from the Upper Triassic of the Newark Supergroup, eastern United States, and its biochronological significance
Four specimens of the aetosaur Stegomus are known from Upper Triassic strata of the Newark Supergroup of the eastern United States. These specimens represent a small aetosaur with a long narrow carapace that is distinctly waisted in front of the hindlimbs, has paramedian scutes much wider than long and lateral scutes that lack spikes. Stegomus is thus remarkably similar to Aetosaurus Fraas, but has weaker sculpturing on its scutes. This is the principal difference between the two, so we regard Stegomus as a junior subjective synonym of Aetosaurus and recognize a distinct Newark species, Aetosaurus arcuatus (Marsh).Aetosaurus in the Newark Supergroup is of biochronological significance because the genus has a broad distribution and one of its occurrences can be directly cross-correlated to Triassic marine biochronology. Aetosaurus is of early-mid Norian age in the German Lower and Middle Stubensandstein. Aetosaurus has been found in mid Norian marine limestones in Italy correlated to the Himavatites columbianus ammonite Zone, which directly cross-correlates the genus to the standard global chronostratigraphical scale. Aetosaurus is present in the Bull Canyon Formation (Chinle Group) of eastern New Mexico, USA and in the Orsted Dal Member of the Fleming Fjord Formation in Greenland; both of these units are of early Norian age. Aetosaurus localities in the Newark Supergroup are of mid Norian age, a conclusion consistent with Newark palynostratigraphy and magnetostratigraphy. Aetosaurus is thus an index fossil of the lower-middle Norian.