Circum-Mediterranean Oligo–Miocene biogeographic evolution – the gastropods’ point of view

Based on studies in Iran (Qom Basin, Esfahan-Sirjan Basin, Zagros Mountains), in Turkey (Mut and Sivas basins), in the Mesohellenic Basin, and in northeastern Egypt, a new palaeobiogeographic concept for the Oligocene and Miocene in the circum-Mediterranean area with special emphasis on the x distribution patterns of gastropod faunas is presented. A very strict biogeographic terminology is proposed to avoid the common fusion of geographic, faunistic and geodynamic terms in the palaeontologists' jargon. Our main interest focuses on the affinities and the faunistic interactions between the 'early Mediterranean' and the 'early Indo-Pacific' regions during the Oligo-Miocene. Especially the role of the early Indo-Pacific faunas as the mythic centre of origination of Early Neogene European mollusc faunas, as often vaguely indicated in the literature, is critically evaluated. This leads to the establishment of a Mediterranean-Iranian Province and a Western Indian-Eastern African Province as palaeobiogeographic subunits of the Western Tethys Region during the Oligocene. Due to major geodynamic and related biogeographic changes in the Early Miocene the Western Tethys Region no longer existed and was replaced by the Proto-Mediterranean-Atlantic Region. For the area of the Paratethys the palaeobiogeographic unit Danubian Province, which includes the Proto-Caspian Subprovince, is proposed. Furthermore, the underrated transatlantic communication of the Oligo-Miocene nearshore mollusc faunas is demonstrated. Altogether this paper is a contribution to the discussion on the biogeographic concepts, classification and nomenclature in palaeontology as initiated by Westermann [Palaeogeogr. Palaeoclimatol. Palaeobiogeogr. 158 (2000) 1-13; 163 (2000) 49-68].