Systematics and palaeoecology of marine vertebrates from the Pietra leccese formation (Miocene, Italy): an integrated approach.

The Pietra leccese is a calcareous formation widely exposed in the Salento Peninsula (south Italy) and its age spans between the late Burdigalian and the early Messinian. The Pietra leccese formation is widely known for its abundant marine vertebrate fossil content that includes bony and cartilaginous fishes, chelonians, crocodiles, sirenian and cetaceans (representing the most common taxa). Even if this rich fossil assemblage has been studied for a long time, there are many specimens from the Pietra leccese formation that remained undescribed. In this thesis, some important specimens from this formation have been studied, providing a description and a systematic framework. More precisely, such an investigation includes: the first fossil record of Molidae (Actinopterygii, Tetraodontiformes) from the Pietra leccese assemblage, an isolated cetacean tooth referred to the family Inticetidae (Cetacea, Odontoceti), a new macroraptorial sperm whale (Cetacea, Odontoceti, Physeteroidea) with accession number MSNUP 17076 from the Tortonian strata of the Cisterna quarry and a novel medium-sized physeteroid (Cetacea, Odontoceti, Physeteroidea) with accession number MSNUP 16954 from the Burdigalian deposits in the vicinities of the Cursi village. This latter is affected by a strong dorsoventral compression due to the diagenesis. Since this feature would have complicated the study of this important fossil sperm whale, its cranium, the most diagnostic preserved skeletal part, has been digitally retrodeformed. Furthermore, the finite element analysis (FEA) is here used to simulate the biting action of the macroraptorial sperm whale Zygophyseter varolai from the lower Upper Miocene deposits of the Cisterna quarry. The presence of Molidae in within the Pietra leccese well matches with the palaeoenvironmental signal from this formation and with the well-known fossil ichtyofauna from the Cisterna quarry. Considering the age and the global distribution of inticetids, likely these toothed whales dispersed via the Caribbean Region and the Central American Seaway, thus suggesting that there was a faunal interchange between the Mediterranean Sea and the Indo-pacific realm in the Lower Miocene. The macroraptorial sperm whale MSNUP I-17076 provides new clues about the faunal composition of the Pietra leccese formation and indicates that several macropredator species (both sperm whales and cartilaginous fishes) inhabited the Mediterranean Basin during the Tortonian. Results from the finite element analysis demonstrates that Z. varolai exerted a bite force comparable to that of an adult great white shark, and thus that it likely fed upon medium-sized marine vertebrates. The high gap values between the anterior and the posterior bite force in Z. varolai, the resulting stress pattern distribution and the general cranial and dental architecture suggest that likely this macroraptorial sperm whale fed via ‘grip-and-shear’ feeding, snapping the food items with an anterior bite and then cutting them with a powerful posterior bite. The study of MSNUP I-16954, greatly aided by the digital retrodeformation, reveals that this sperm whale belongs to a new taxon currently unnamed. The new species reported here enrich the taxonomic diversity and morphological disparity of the wide Burdigalian stock of sperm whales. Moreover, it contributes to define the late Early Miocene as a radiation period for Physeteroidea, which during this period occupied several diverse trophic niches.