• beaked whales
• mesoplodon
• Paleobiogeography

In the following master's thesis, the geographical distributions of over 50 extinct and extant species
of beaked whales (Ziphiidae, Cetacea) have been examined.
To resolve some open systematic issues, some fragmentary skulls (i.e. rostra) of ziphiids from Pliocene of Italy, have been revised. These rostra were previously referred to Mesoplodon longirostris or Mesoplodon sp. After a redescription and comparison with other species, characterized by the presence of a similar ossified vomer, these rostra have been as assigned to indeterminate hyperoodontines, since none of the characters currently used in the generic and specific identification of these cetaceans are present in this material. Despite the identification only at the subfamily level, we have confirmed the presence of hyperoodontines in the Mediterranean as early as the Pliocene, obtaining important paleobiogeographic information for the paleobiogeographical analysis.
The paleobiogeographic analysis was carried out using both S-DIVA and a Bayesian method, which identified possible dispersal and vicariance events within this family. Two phylogenetic analyses were performed: a morphological one with molecular constraints using the PAUP software and a Bayesian one using the Beast software, which allowed for temporal calibration of the nodes.
This study confirms that beaked whales originated during the Middle Miocene in the Northern
Hemisphere, specifically in the North Sea, and colonized lower latitudes only in the Late Miocene. Specifically ziphiids spread into the central Pacific during the Tortonian, when we witness the first major radiation of these cetaceans, which subsequently began to venture into the Southern Hemisphere as well.
Environmental factors and selective pressures, such as climate change, the radiation of delphinids, and internal competition within the family, led to the decline of tropical species. Over time, these factors triggered various dispersal and subsequent vicariance events, which gave rise to the modern distribution of beaked whales and their occupation of narrow ecological niches. These events were highlighted by the aforementioned software.
Although problems in dating several specimens hindered researchers from determining the exact steps in the distribution of subfamilies, we can hypothesize that the subfamily Berardinae, along with the extinct clade Messapicetiformes, originated in the North Atlantic. Berardinae are still confined to the two circumpolar zones and rarely venture into lower latitudes. On the other hand, the Messapicetiformes have always remained confined to the northern Atlantic, except for some species that crossed the Atlantic and colonized the coasts of Peru.
The other two subfamilies likely originated in the Southern Hemisphere before undergoing a rapid dispersal, eventually recolonizing the North Atlantic and entering into competition with the Messapicetiformes. Today, members of the Ziphiinae and Hyperoodontinae subfamilies are the most widespread beaked whales, displaying the most extensive distributions, with some species even being cosmopolitan.