Belemnite distribution patterns - Implications of new data from Argentina

Belemnites are nekto-pelagic cephalopods which developed a widespread pattern of distribution in the Jurassic, and most authors have accepted that their centre of origin was Europe. Available data suggest that the belemnites developed a global distribution only in the Toarcian, some 15 Ma after their first appearance in the European Hettangian. Development of the Boreal and Tethyan belemnite realms took place in the Mid-Jurassic and continued through to the Cretaceous. New data from Argentina reaffirms the development of global distribution of belemnites in the Toarcian, and sheds new light on biogeographical patterns for the later Jurassic and Cretaceous of the Southern Hemisphere. Oxygen-isotope palaeotemperatures obtained from belemnite skeletal carbonates from the Antarctic Peninsula indicate that there was a significant cooling in the Valanginian to Aptian time periods. This appears to correlate with the development of an Austral Realm; but it does not explain the absence of the Austral Realm in the Jurassic. Future work on the palaeotemperatures from Argentine belemnites may help confirm this relationship. This has considerable implications for understanding the development of marine faunal realms in the Mesozoic.