Suture investigations and the classification of Cretaceous heteromorph ammonites

Abstract

Investigating the suture and shell ontogeny of Ptychoceras it can be shown that also in turrilitids unstable quinquelobate primary sutures are found besides quadrilobate ones. However, all Cretaceous heteromorphs and recoiled descendants pass through a quadrilobate suture stage at least beyond the primary constriction. This is considered to define the presumably monophyletic but still cryptogenic Ancyloceratina. Neither quadrilobate primary sutures nor bifid lateral lobes ( L, U 1) allow the separation of an own suborder Turrilitina, Beznosov & Mikhailova. Bifid and trifid lateral lobes were found to co-occur in the same species.