EARLY CRETACEOUS (PRE-APTIAN) AMMONITES OF THE MEDITERRANEAN TETHYS -PALEOECOLOGY AND PALEOBIOGEOGRAPHY

This study focuses on Late Valanginian and Barremian ammonite assembla ges of the Mediterranean Tethys. Their palaeobiogeographic distributio n shows that the faunal composition is ecologically controlled. Shelf assemblages differ from those reported from epioceanic areas. The numb er of families (regarded as major morphologic types) increases during the Early Cretaceous. reaching a peak in the late Barremian. Opportuni stic strategy has been suggested for some taxa (Leptoceratoidinae, Boc hianitidae). 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 dista l 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 blo om? and the evolution of the ammonites living mainly on the shelf marg ins and distal, epioceanic environments cannot be disregarded to expla in some ammonoid evolutionary events during the Early Cretaceous. (C) 1998 Elsevier Science B.V.