• cladistic analysis
• delphinidae
• fossil record
• osennae
• Siena basin
• tursiops

A fossil specimen of l Delphinidae (Cetacea, Odontoceti) discovered by Simonelli in 1911 near San Quirico d’Orcia (Siena, Tuscany, Italy) is revised. The specimen consists of a fragmentary skull (basicranium, occipital shield, temporal fossae and nasals are lacking), a small anterior portion of the left mandible, the right periotic (almost complete), the right and left bullae (both lack the lateral side and the posterior process) and the atlas fused with the centra of the axis and of the 3rd and 4th cervical vertebrae.
The specimen was described by Simonelli (1911) as holotype of the fossil species Tursiops osennae, but it differs from extant Tursiops spp. in many characters, the most significant are: (1) shorter rostrum, similar to Cephalorhynchus, Hemisyntrachelus and Sagmatias, (2) anterior angle between nasals, measured using the fossae preserved in the frontals, very large, only comparable with Hemisyntrachelus, and (3) shorter anterior process of periotic, with ratio between length of pars cochlearis and the length of the process similar to the one of Astadelphis and Leucopleurus. For this reason, the specimen is named “Tursiops” osennae until a new genus is established for this species. A cladistic morphological analysis, also using a molecular scaffold approach, was performed to examine the phylogenetic relationship between this species and the other fossil and extant delphinids.
The holotype of “Tursiops” osennae was discovered in Pliocene sediments, deposited from the Zanclean to the middle Piacenzian age. The estimated maximum stratigraphic distribution of this species is from 5.3 to 3.35 Ma and the minimum from 4.65 to 4.15 Ma.
“Tursiops” osennae corroborates fast speciation-extinction rate and the explosive rise of the delphinids during the Plio–Pleistocene. The fast and significant climate changes occurred during the Pliocene epoch can partially explain this explosive radiation, along with the partial isolation of the Mediterranean and the rapid tectonic evolution of the sedimentary basins of southern Tuscany.