I cetacei odontoceti del Miocene Inferiore del Bacino Veneto-Friulano: studio sistematico, caratterizzazione paleoecologica e contestualizzazione paleoambientale

The following work concerns the systematic description and palaeoecological and palaeoenvironmental characterisation of the fossil odontocetes found in the rocks of the Lower Miocene of Veneto, formed by sediments which were deposited in the Venetian-Friulian Basin, between roughly 21 and 19 Ma. In general, the molassic infills of the Venetian-Friulian Basin were deposited since the final age of the Oligocene (Chattian) and nowadays constitute a sedimentary succession of the Oligo-Miocene, exposed in the Belluno Valley (northeastern Italy, Veneto). The sediments deposited during the Oligocene and Miocene were later deformed within the framework of the uplift of the Alps, now forming an asymmetrical syncline. This fold stretches from the Belluno area and the Alpago (northeast) to Feltre (southwest), and the rocks making this structure are informally called “Molassa Bellunese” (=Belluno Molasse), being part of the “Molassa Veneto Friulana”, (including the strata in Friuli and southern to the Bellunes Prealps). Many fossil odontocetes were recovered from the rocks of the Lower Miocene of this sedimentary succession, in particular from the “Arenarie di Belluno” (= Belluno Sandstones), initially and exhaustively described by Giorgio Dal Piaz at the beginning of the 20th century, and later revised by Giorgio Pilleri in the 1980s. Despite the diversity of the assemblage of toothed whales coming from the Belluno area, these fossils lack precise chronostratigraphic dating, due to poor geochronological constraints. This imprecise dating of the odontocetes of the Belluno area discouraged further investigations on the palaeoecological and palaeoenvironmental context of this fauna, other than the rediscussion of the palaeobiological and evolutionary meaning of this association. The finding of new fossils of toothed whales and other marine vertebrates, from a new fossiliferous locality nearby Feltre (southwestern end of the Belluno Valley), made possible the birth of this doctoral project. The new site, named Colle della Croce quarry, represents a more distal portion of the Venetian-Friulian Basin compared to Belluno, thus allowing the dating of the sediments exposed therein (typically marls, eteropic relative to the sandstones of the Belluno area), thanks to biostratigraphic markers (nannoplankton), never found in the sediments associated with the findings from Belluno. After the historical introduction to the issues presented above, the thesis, focused on the systematic description of the new specimens, aimed at highlighting the specimens of two families never recorded from the Belluno area: Kentriodontidae and Squaloziphiidae. In the first chapter, the first record of the genus Kentriodon from the proto-Mediterranean area is presented, further constituting the oldest record of this genus, unambiguously identified as such taxonomically. Within the second half of the chapter, a new species of Kentriodon is introduced, described on the basis of 10 specimens found in the Chilcatay Formation exposed in the Ica desert (Peru). In the second chapter, a new genus and species belonging to the family Squaloziphiidae is described. This new taxon is distinguished from other squaloziphiids by a proportionally shorter rostrum, larger teeth and a wider, rectangular vertex, wider than long, and with the anterior margins of nasals converging anteromedially. In the third chapter, the whole fossil assemblage of the Colle della Croce quarry is described, consisting of representatives of six families and two clades of odontocetes (Squalodontidae, Eurhinodelphinidae, Kentriodontidae, Squaloziphiidae, Dalpiazinidae, Neosqualodontidae, Platanidelphidi and Physeteroidea), divided between two formations, the Libàno Sandstone Formation (uppermost Aquitanian) and the Bolago Marl Formation (basal Burdigalian). In the fourth chapter, the anatomy of Squalodon peregrinus is described here in detail for the first time, this species being a heterodont odontocete, first found near Belluno and later in Feltre as well, well distinguished from the other members of the family Squalodontidae by the globose proportions of the wider than long neurocranium, the pachyosteosclerosis of the pre and postorbital processes of the frontal and by a rostrum probably proportionally shorter than the other members of the genus Squalodon. In the fifth chapter, the taphonomic features of the fossils of the Colle della Croce quarry are discussed, along with some peculiar phenomena characterising the preservation of the vertebrate remains of Feltre. In the sixth and last chapter, the fossil assemblages of odontocetes, found within the sediments of the Lower Miocene, all over the world, are examined, discussing possible affinities and differences of the fossil assemblage of the Lower Miocene of the Venetian-Friulian Basin.