The palaeobiogeographical history of the Western Mediterranean before the Quaternary: decoding biotic evidence

Because of its high level of biodiversity and rate of regional endemism in both the present and past, the Mediterranean Basin is a hotspot for biogeographical studies. Mediterranean geology has been shaped by the interplay between the African and European plates along with smaller intervening microplates. The evolution of the Western Mediterranean Basin started about 30 Ma due to migration of orogenic belts and widespread extensional tectonics of back-arc basins. This complex geological history caused repeated isolations/connections of insular and mainland territories that led to a peculiar biogeographical history of the main insular realms (Balearic, Sardinia and Sicily islands, Tusco-Sardinia, and Abruzzi–Apulia palaeobioprovinces). Although few African lineages have been claimed to be present in Sardinia, most of Balearic, Tusco-Sardinian and Abruzzi–Apulian settlers had a European origin, while Sicily, an island since the Late Pliocene, and Southern Calabria were parts of a mainland, extending at the northern border of the African plate. The patterns of faunal evolution mainly depend on palaeogeographical control, resulting from the interaction of geodynamic events and marked sea level fluctuations, e.g. at the time of the Messinian Salinity Crisis. Reconstructing timing, modes and “routes” of dispersal is a challenging task. Alternating connections with the Paratethys played a prominent role in the distribution of non-marine and marine molluscs. Insights from plants suggest that part of the modern genetic structure of Mediterranean populations may be traced back to the Tertiary history of taxa, which could help in delineating pre-Quaternary palaeobiogeographic scenarios.