Reassessing the sedimentary deposits and vertebrate assemblages from Ponte Galeria area (Rome, central Italy): an archive for the Middle Pleistocene faunas of Europe

Abstract

The Ponte Galeria area is part of the larger "Campagna Romana" and hosted the inner delta of the Tiber River since the beginning of the Middle Pleistocene, allowing the deposition of a series of glacio-eustatically controlled fluvial-lacustrine sedimentary successions very rich in fossil mammal remains. Due to its richness of fossiliferous sites, this area represents an exceptional archive for the study and understanding of the biochronological, paleobiogeographical and paleoenvironmental evolution during the Middle Pleistocene in Europe. A series of recent studies, using the 40Ar/39Ar ages of tephra intercalated within the sedimentary deposits, provided a large amount of geochronological data linking these aggradational successions to the different Marine Isotopic Stages. In the present paper we present a complete review of the faunal assemblages identified so far in the Ponte Galeria area, and we constrain the ages of the faunal units by placing them within the new chronostratigraphic scheme. By means of this interdisciplinary approach, we re-calibrate the mammal assemblages collected in this area and reconstruct a new biochronological and paleobiogeographic framework for the Italian peninsula during the Middle Pleistocene. In particular, we distinguish six well-defined biochronological units (Slivia, Ponte Galeria, Isernia, Fontana Ranuccio, Torre in Pietra, and Vitinia) in the studied area covering a time span of ca 0.6 Myr, from the Early to Middle Pleistocene transition to at least marine isotope stage 7. This period is characterized in Europe by the Mid-Pleistocene Revolution (global climate change) and by the transition at first between Villafranchian and Galerian taxa and later between the Galerian and Aurelian ones. According to the reviewed data, the persistence of Villafranchian taxa is recorded in Italy at the beginning of the Middle Pleistocene probably due to favorable climatic conditions or delay in dispersal of competitive species, while the faunal turnover between the Villafranchian and Galerian species was completed around 0.6-0.5 Ma. During this time, Bos primigenius and other temperate-warm taxa were widespread in the Peninsula earlier than in Western Europe. In contrast, typical Aurelian taxa, usually related with temperate-cold climatic conditions (Ursus spelaues, Megaloceros giganteus), occurred later in Italy than in other Western European areas.