Parathethyan ostracod immigrants in Italy during Late Miocene.

During Serravallian, the emersion of the Carpathians and of the Alpine foreland domain closed the northern connection between the western and the eastern Tethys. In the late Miocene this latter became subdivided into several basins (Vienna Basin, Pannonian Basin, Dacic Basin, Ponto-Euxinic Basin and Caspian-Aral Basin) which, due to the freshwater input from several important rivers, were progressively characterised by brackish waters. The connection via the present Dardanelli straight was still open but the different salinity between western and eastern Tethys represented an ecological barrier, preventing the faunistic exchanges and causing the onset of two different Late Miocene bioprovinces: the Paleomediterranean bioprovince to the west and the Paratethyan bioprovince to the east.Notwithstanding the Late Miocene isolation of Paleomediterranean from Paratethys, during Late Tortonian-early Messinian it is possible to recognise in Italy few brackish and freshwater ostracods with Paratethyan affinity. The palaeogeography of the area prevents to suppose a normal aquatic migration, and, indeed, the distribution of several Paratethyan genera seems disjuncted. In this case, only a passive dispersal by aquatic birds can be claimed. Paratethyan genera transported in Italy are Camptocypria (Sirmiella), Bakunella, Propontoniella, Labiatocandona, Zalanyiella (all included in the Subfamily Candoninae), Loxoconchissa s.s. and Loxoconchissa (Loxocaspia), included in Family Loxoconchidae and Amnicythere (and may be Chartocythere and Mediocytherideis) included in Family Leptocytheridae.During the latest Messinian lago-mare event, the closure of the Atlantic-Mediterranean connection and the subsequent humid global climate phase caused a salinity lowering of the Paleomediterranean waters. The ecological barrier between Paleomediterranean and Paratethys was disrupted and an important contingent of Paratethyan ostracods migrated westwards colonising the Paleomediterranean, whose endemic fauna was severely impoverished by the Messinian salinity crisis and the following water dilution. The Italian (and Paleomediterranean) latest Messinian lago-mare deposits are characterised by Paratethyan species such as Caspiocypris pontica, Lineocypris cf. L. fossulata, Lineocypris cf. L. hodonensis, Pontoniella pontica, Zalanyiella venusta, Amnicythere accicularia, Amnicythere anormalis, Amnicythere cellula, Amnicythere costata, Amnicythere idonea, Amnicythere pontica, Amnicythere lata, Amnicythere litica, Amnicythere multituberculata, Amnicythere palimpsesta, Amnicythere propinqua, Amnicythere cf. A. rosalinae, Amnicythere subcaspia, Euxinocythere (Maeotocythere) praebaquana, Euxinocythere (Maeotocythere) bosqueti, Loxoconcha (Loxoconcha) eichwaldi, Loxoconcha (Loxoconcha) muelleri, Loxoconcha rhombovalis, Loxoconcha cf. L. schweyeri, Loxocorniculina djafarovi, Pseudocythere limata, Cytherura pyrama, Tyrrhenocythere ruggierii, Tyrrhenocythere pontica.