Early Cretaceous (pre-Aptian) ammonites of the Mediterranean Tethys: palaeoecology and palaeobiogeography

This study focuses on Late Valanginian and Barremian ammonite assemblages of the Mediterranean Tethys. Their palaeobiogeographic distribution shows that the faunal composition is ecologically controlled. Shelf assemblages differ from those reported from epioceanic areas. The number of families (regarded as major morphologic types) increases during the Early Cretaceous, reaching a peak in the late Barremian. Opportunistic strategy has been suggested for some taxa (Leptoceratoidinae, Bochianitidae). The increased diversification of the ammonite faunas from Valanginian to Barremian reflects an increase of the number of niches. Possibly the progressive radiation and adaptation to different distal marine environments is the result of a more and more specialized use of food resources. A possible link between the trophic opportunities, which developed as a consequence of the late Tithonian nannoconid bloom. and the evolution of the ammonites living mainly on the shelf margins and distal, epioceanic environments cannot be disregarded to explain some ammonoid evolutionary events during the Early Cretaceous.