Systematic palaeontology of the Perisphinctoidea in the Jurassic/Cretaceous boundary interval at Le Chouet (Drôme, France), and its implications for biostratigraphy
Authors
Camille Frau
Groupement d’Intérêt Paléontologique, Science et Exposition, 60 bd Georges Richard, 83000 Toulon
Luc G. Bulot
UM 34 Aix-Marseille Université ; CNRS (UMR 7330) ; IRD (UMR 161), Centre Saint-Charles, Case 67, 3 Place Victor Hugo, 13331 Marseille Cedex 03
William A.P. Wimbledon
School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ
Christina Ifrim
Institut für Geowissenschaften, Ruprecht-Karls-Universität, Im Neuenheimer Feld 234, 69120 Heidelberg
Keywords:
Ammonites, Berriasian, Cretaceous, Biostratigraphy, Le Chouet, France
Abstract
This study describes ammonite taxa of the Perisphinctoidea in the Jurassic/Cretaceous boundary interval at Le Chouet (Drôme, France). Emphasis is placed on new and poorly known Himalayitidae, Neocomitidae and Olcostephanidae from the lower part of the Jacobi Zone auctorum. Significant results relate the introduction of Lopeziceras gen. nov., grouping himalayitid-like forms with two rows of tubercles, and Praedalmasiceras gen. nov., grouping the early Berriasian Dalmasiceras taxa. Study of the ontogenetic sequences of both genera show that they were derived from late Tithonian Himalayitidae. This supports the distinction between the subfamilies Himalayitinae and Dalmasiceratidae subfam. nov. Content, variation, dimorphism and vertical range of the Neocomitidae Berriasella, Pseudoneocomites, Elenaella and Delphinella are discussed. A conservative use of the Olcostephanidae Proniceras is followed herein.
