The Cravenoceras leion Marine Band at Backdale Mine has yielded a stratigraphically important ammonoid fauna consisting of the species Cravenoceras leionBisat 1930, Edmooroceras medusa (Yates 1961) and Girtyoceras sp. C. leion, in particular, is represented by well preserved material, allowing the description of the entire ontogeny. It is demonstrated that the conch geometry of this species undergoes major transformations, and that the suture line is characteristic of the genus Cravenoceras. Based on the ontogenetic development of the suture line, a clear separation can be made from the Rhenish species Emstites schaelkensis (Brüning 1923).

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