PALEOBIOGEOGRAPHY OF EARLY-LATE CRETACEOUS INOCERAMIDS IN THE CONTEXTOF A NEW GLOBAL PALEOGEOGRAPHY

Inoceramids had their evolutionary maximum during the Late Cretaceous. Inoceramid frequency displays fluctuations partly in response to sea level changes. Regressions and lowstands correspond to a rise in the t otal number of species, reflecting restricted communication between re gions and differentiation of oceanographic conditions. The faunal simi larities between the epicontinental seas in North America and western Eurasia and the basins in the northwestern Pacific area show a decline from the Cenomanian to the Coniacian. In the Cenomanian and early Tur onian a more or less continuous faunal exchange occurred. Close relati ons with some interruptions are evident for the middle to the late Tur onian. From the late Coniacian onwards the Pacific area was characteri zed by its own, separate development. The greatest faunal similarities existed between North America and western Eurasia. In the context of a new paleogeographical reconstruction for the Cretaceous it is appare nt that both regions belong to the North Atlantic-western Tethys Ocean which was nearly enclosed on all sides. The latter was probably chara cterized by a restricted oceanographic exchange towards the Pacific oc ean.