The significance of Mediterranean ammonites with regard to the traditional Jurassic-Cretaceous boundary

We discuss the significance of Mediterranean faunas in the study of the traditional Jurassic-Cretaceous boundary based on ammonites. Reviewing the record of ammonites and calpionellids from southern Spain and also discussing data from SE France, Bulgaria, Czechoslovakia, Cuba, Mexico and Argentina, which permit correlation with the Spanish faunas, we conclude that: a) Berriasella jacobi Mazenot is a good index fossil for the base of the Berriasian (=base of the Cretaceous System), b) the jacobi ammonite association clearly differentiates the latest Tithonian (Durangites Zone), c) the genus Kossmatia occurs in shelf deposits and, when present, is very rare in the European Tethys, d) the Mexican Gulf was not the centre of dispersal for Durangites or Kossmatia .