[Proceedings of the symposium 'Molluscan Palaeontology' : 11th International Malacological Congress, Siena (Italy) 30th August - 5th September 1992 / A.W. Janssen and R. Janssen (editors)]: Palaeobiogeographical observations on Villafranchian continental molluscs of Italy

In this paper the palaeobiogeographical affinities of Villafranchian continental molluscan faunas of Italy are examined. The best known Early Villafranchian (= Middle Pliocene) assemblages come from the Piedmont Basin which delivered a rich malacofauna dominated by archaic pulmonates, studied a hundred years ago by Sacco. New sampling in this basin by the authors of this paper have permitted to find some other palaeobiogeographically interesting taxa. Many taxa indicate strong affinities with west-European basins (France, western Germany). In central Italy, recent findings in deposits of the Tiberino Basin (Umbria) have pointed out a good number of Early Villafranchian pulmonate species common to the Piedmont Basin and some endemic aquatic prosobranchs. A different palaeobiogeographical history arises from the analysis of an Early Villafranchian fauna collected in western Sardinia. A strong affinity with Balearic and Iberian regions is evidenced. Molluscan assemblages of Middle Villafranchian (= Late Pliocene) age in Italy are poorly known. Late Villafranchian (= Early Pleistocene) continental molluscs come from many localities of northern and central Italy. The best studied faunas are those of the basins of Valdarno, Valdichiana and the Tiberino (western side of central Italy). In these basins the assemblages are dominated by endemic aquatic prosobranchs but some elements with western or east-European affinities are also present. Numerous Early Villafranchian genera and species of pulmonates are lacking in the sediments of Late Villafranchian age. Probably they became extinct in coincidence with the onset of the first large ice sheet on the Northern Hemisphere, at the Gauss/Matuyama-boundary (c. 2.6 Ma BP). Late Villafranchian pulmonates are represented mostly by modern species, whereas archaic elements are dominant among the mostly endemic prosobranchs of this age. These last-mentioned elements do not cross the Early/Middle Pleistocene boundary (c. 0.8 Ma BP), i.e. they do not survive the first strong climatic crisis of the Quaternary. On the whole it results that since the beginning of the Middle Pleistocene clear modern features are shown by the continental molluscan faunas of Italy, both at genus and at species level. This work has been supported by a M.P.I, grant 60% (2.09.02.157).