Change in diversity, ecological significance and biogeographical relationships of the Mediterranean Miocene toothed whale fauna

The main evolutionary trend in the Mediterranean Miocene toothed whale fauna is related (1) to the change in diversity and (2) to the turnover in community structure. Diversity increases from Upper Aquitanian-Lower Burdigalian to Burdigalian-Langhian, when it reaches its maximum. Starting from this time, diversity decreases progressively. The Early Miocene (Upper Aquitanian-Lower Burdigalian) Mediterranean toothed whale fauna, as well as the extramediterranean ones, is characterised by a high number of endemic taxa and by the prevalence of longirostral forms living in estuarine-neritic environments. A more diversified fauna spreading in neritic and pelagic environments characterises the Burdigalian-Langhian age, while an increase in pelagic forms and the nearly complete disappearance of some archaic longirostral taxa is typical of the Serravallian-Messinian fauna. Decrease in diversity and disappearance of archaic longirostral taxa are also recorded, at more general scale, in the Late Miocene extramediterranean fossil bearing deposits. These events can be related to the progressive global climatic deterioration, starting from Middle Miocene. From a biogeographic point a view, we can outline some relationships between the Mediterranean and western North Atlantic Miocene faunas. Closer affinities are observed between the Baltringen fauna and the northern Atlantic one, because of the presence of the genera Pomatodelphis and Zarhachis (platanistids) in both areas. In the Miocene Mediterranean and in North Atlantic, the delphinids are apparently absent as well as other extant delphinoid groups even if erroneously recorded in the past