The Miocene land-vertebrate fossil site of Scontrone (Central Apennines)

In the early nineties of the last century, a Miocene fossil site yielding numerous teeth and bones of land mammals, together with abundant remains of chelonians and crocodiles, was discovered at the southern border of the Abruzzi National Park (Central Apennines) near the village of Scontrone. The mammalian fauna of Scontrone shows close similarities to a fauna discovered in the Gargano region about twenty years before. The endemic characters of the Scontrone and Gargano associations suggest the existence of a paleobiogeographic province isolated from the nearest mainland areas. The present paper synthesizes the results of a detailed geological study aimed at defining the stratigraphic position and the depositional setting of the vertebrate bonebeds. The paper, in addition, provides some information on the time in which the mammal colonization took place and on the migration route followed by the new incomers to reach the Scontrone-Gargano region. The Scontrone land vertebrates are embedded in coastal-tidal-flat carbonates locally preserved at the base of the Lithothamnium Limestone, a Miocene carbonate-ramp depositional unit characterized by a rich rhodalgal facies widespread in the Central-Southern Apennines and, more in general, in the whole Mediterranean region. The age of the base of the Lithothamnium Limestone, and consequently the age of the Scontrone vertebrate fossil association, is Tortonian, not older than the N16 Zone after the First Regular Occurrence of Neogloboquadrina acostaensis (a bioevent astronomically dated at 10.554 Ma). The colonization of the terrestrial mammals, on the contrary, is much older as it dates back to the latemost early Oligocene, at 29-30 Ma, when an important global sea level drop exposed the Apulia Platform and a part of the Central Adriatic region creating a landbridge that allowed the terrestrial fauna migration from Dalmatia to Gargano via the Tremiti Islands. The following marine transgression (maximum flooding was reached during the Langhian, i.e. between 16.4 and 14.8 Ma) lead to the isolation of the Apulia Platform and brought about, as a consequence, a secluded paleobiogeographic province where land vertebrates endemized, flourished and diversified. The Miocene Scontrone fossil fauna represents an exceptional case, in the Central Apennines, of land vertebrate finding related to the occurrence, during Tortonian times, of a wide coastal plain where tidal flats, ephemeral marshes and coastal lagoons created favourable conditions for life matched with optimal conditions for fossilization. Owing to the presence of ravinement surfaces associated with subsequent transgressive events, sedimentary records of paralic environments at the base of the Miocene ramp carbonates are rarely preserved in the Apennines.