First discovery of nautilids from the Albian–Cenomanian succession of the Koppeh Dagh Basin, NE Iran

The Aitamir Formation, situated in the Koppeh Dagh Basin in the northeast of Iran, is known for its well-exposed Albian-to-Cenomanian succession. Although geologists previously documented a number of macro- and microfossils, no nautilids had been discovered until now to our knowledge. Here, we present lower Albian and middle Cenomanian nautilids from the Koppeh Dagh Basin for the first time. This discovery is also the first record of Cretaceous nautilids from Iran. We identified the specimens as Eutrephoceras clementianum (d’Orbigny 1840), E. sublaevigatum (d’Orbigny 1850), E. bouchardianum (d’Orbigny 1840) and Eutrephoceras sp. These specimens occur in horizons situated between several ammonite-bearing levels, which allowed us to more precisely constrain age estimates for the recovered nautilid specimens. E. clementianum could not be dated precisely but likely comes from between late Aptian ammonite index Hypacanthoplites uhligi and middle Albian Hoplites (Hoplites) baylei. E. sublaevigatum occurs just above the late Albian ammonites Mariella bergeri and Semenoviceras michalskii and below the Mantelliceras mantelli Zone. At the upper part of the section, E. bouchardianum and Eutrephoceras sp. were collected from lower Albian beds, which correspond to the Mantelliceras mantelli and Mantelliceras dixonii zones. These new findings contribute to our knowledge of the geographical distribution and stratigraphic range of Albian–Cenomanian nautilid species.