SYSTEMATICS AND PALAEOBIOGEOGRAPHY OF A GENUINE EUROPEAN GENUS, EUROPICARDIUM POPOV, 1977 (BIVALVIA, CARDIIDAE)

Europicardium Popov, 1977 was introduced for some Cenozoic cardiids from Europe (Schneider, 2002). In most literature, even in the most recent, this genus has been overlooked or confused with Trachycardium Mörch, 1853, which is a distinct genus living in the tropical American waters. The best known Europicardium species is E. multicostatum (Brocchi, 1814), type species. The present work, though at a preliminary stage, tries to review the fossil species of Europicardium, and to outline the palaeogeography of the genus. According to Schneider (2002), Europicardium includes four Neogene species of Europe and North Africa: E. multicostatum (Brocchi, 1814), E. polycolpatum (Cossmann & Peyrot, 1911), E. pseudomulticostatum (Zhizhchenko, 1934) and E. badeniense (Kókay, 1996). Three living species are known from the tropical West Africa, E. caparti (Nickles, 1955) being the best known. The present revision allowed the distribution of E. multicostatum to be better defined, i.e. Pliocene to Early Pleistocene of the circum-Mediterranean area, excluding the older records reported in literature, and to put E. polycolpatum in synonymy with E. miorotundata (Sacco, 1899), originally described as a Miocene variety of Trachycardium multicostatum. It is known from the Early Miocene of Aquitaine, Middle Miocene of Paratetheys and paleo-Mediterranean. E. pseudomulticostatum is from the Middle Miocene of Crimea, Ciscaucasia and Transcaucasia (Eastern Paratethys), whereas E. badeniense is from the Middle Miocene of Hungary (Central Paratethys). Another Paratethyan species, from the Vienna basin, misidentified as multicostatum since Hoernes (1862), proved to be distinct and will be described as new. Other possible distinct species are the varieties mioangulata and miocaudata, both described by Sacco (1899) on scarce and fragmentary material from the Miocene of the Turin Hill. The oldest records of Europicardium are from the Early Miocene of the Aquitaine basin. This supports Schneider's (2002) hypothesis of strong relations with Loxocardium Cossmann, 1886, from the Paris basin. From the Aquitaine basin, Europicardium widely spred into the paleo-Mediterranean and Paratehtys, reaching a remarkable diversity in the Middle Miocene, probably thanks to the Middle Miocene Climate Optimum. Since the closure of Paratethys and the Pliocene climate deterioration, Europicardium became confined to the Mediterranean, with E. multicostatum, until the Early Pleistocene. Finally, the strong Quaternary climate changes led the genus to withdraw to southern areas, in the tropical waters of Western Africa.