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RESEARCH PRODUCT

AMMONOID EVOLUTION TRIGGERED BY PALAEOGEOGRAPHIC CHANGES: ORIGIN OF OXFORDIAN SUBFAMILY PASSENDORFERIINAE (SOUTHERN TETHYS)

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The comparison of Middle-Upper Jurassic ammonite successions in SW Sicily (Sciacca) and Iberia shows that, during the Middle Jurassic, besides some typical Mediterranean taxa, in Sicily as well as in the Betic Ranges (S Spain) ammonoid successions contain a higher share of typical Submediterranean taxa of Ammonitina, entirely comparable to those recorded in Epicontinental areas of Eastern Iberia. From middle Oxfordian onwards instead, ammonite successions show a clear taxonomic differentiation, being dominated in Sicily by typically Mediterranean taxa (Passendorferiinae) whilst typical Submeditrerranean groups (Perisphinctinae, Oppeliidae) clearly dominant in the Iberian Range, are testimonial to non-existant there. Such biogeographic differentiation seems to match the palaeogeographic evolution of the Western Tethys from the Callovian-Oxfordian boundary onwards, originating the development of epioceanic platforms at the southern margin of Tethys and presumably triggering the divergence and evolution of Passendorferiinae.