The genusLuppoviaand the phylogeny of Cretaceous heteromorphic ammonoids

摘要

The unique preservation of heteromorphic shells ofLuppoviaKakabadze, Bogdanova&Mikhailova 1978 from the Aptian deposits of Bolshoj Balkhan (western Turkmenia) made it possible to study the microstructure, internal shell characteristics and suture ontogeny of this genus. Microstructural investigations revealed that the dorsal shell wall inLuppoviais composed of three layers in contrast to that of monomorphic ammonoids, which is single‐layered. This ability of secreting different numbers of layers in monomorphs and heteromorphs demonstrates plasticity of secreting activity of the mantle epithelium. Data obtained from the study of internal shell structure and suture ontogeny have been compared. Both these methods of investigation lead to the conclusion that the genusLuppoviabelongs to the order Ammonitida. The results obtained confirm the viewpoint that the Cretaceous heteromorphic superfamilies Turrilitaceae and Ancylocerataceae have independent origins and belong to two different orders, Lytoceratida and Ammonitida, respectively. □Ammonoidea, Luppovia,shell structure, ontogeny, phylogeny, Cretace