Werner E. Piller, University of Graz (Austria)
Mathias Harzhauser, Natural History Museum Vienna (Austria)
Andreas Kroh, Natural History Museum Vienna (Austria)
Oleg Mandic, Natural History Museum Vienna (Austria)
Björn Berning, University of Graz (Austria)
Markus Reuter, University of Graz (Austria)
Looking at centers of biodiversity from a geological perspective, particularly considering deep time and geological processes, provides a widely different view on their spatial stability and longevity compared to a pure biological approach. The processes are related to plate tectonics which strongly influence water exchange between ocean basins, migration pathways of marine biota and distribution of habitats. These processes are strongly influenced by and interrelated with global climate.
Paleobiogeographical studies covering the last c. 50 Ma and an area from the modern European Atlantic Coast, via the Mediterranean region, the Middle East, to southern Pakistan/India and Eastern Africa provide a long term insight into its paleogeographic and biogeographic evolution. These studies focus on shallow water biota and include groups such as foraminifers, corals, gastropods, bivalves, bryozoans, echinoderms, and red algae from various sedimentary environments to minimise local environmental disturbances.
During the Eocene the area under study was part of the Tethys Ocean biogeographically representing the Western Tethys Region (WTR). Until the closure of the Tethyan Seaway during the Early Miocene, a marine faunal exchange was enabled via the Mesopotamian Trough and the Zagros Basin, as reflected by contributions of Indonesian corals in the Iranian basins and by the occurrence of ??western'' gastropods in Pakistan and India. The emergence of a landbridge due to Arabian/Eurasian plate collision was preceded in the marine biosphere by first biogeographic divergences on both sides of the seaway already during the late Oligocene (e.g., within tridacnine bivalves and strombid gastropods). Around the closure event, the breakdown of biogeographic relations was near-complete and the Proto-Mediterranean faunas bear little in common with those of the Indo-West Pacific Region (IWPR). Some of the studied biota clearly suggest that the WTR had acted as a centre of origin and diversity during Oligocene and Early Miocene times. After closure of the seaway, this centre had shifted to the southeast, heralding the enormous biodiversity of the modern IWPR. Some originally WTR elements followed this shift and formed the Miocene stock for the modern IWPR faunas. In contrast, the marine fauna in the Mediterranean suffered strong impoverishment due to Miocene cooling, the Messinian Salinity Crisis and the late Pliocene and Pleistocene glacials.
Based on these data we are able to clearly trace gradually shifting biodiversity hotspots through time moving from the WTR over the Mediterranean-Iranian Province and East African-Arabian Province to the Proto-Indo-Polynesian Province during the Oligocene and Miocene. Major practical problems of recognising biogeographic patterns are the heterochronous developments in different systematic groups, which are often obscured by a stratigraphically incomplete and geographically patchy fossil record.