The taxonomic status and biochronological implications of new finds of Oreopithecus from Baccinello (Tuscany, Italy)

Several species of mammals endemic to the late Miocene faunas of the Maremma region of Tuscany in Italy are known to have undergone a significant degree of morphological change during the time interval between the deposition of V-1 and V-2 horizons at Baccinello. This raises the interesting question of whether or not Oreopithecus, which occurs in association with both V-1 and V-2 faunas, exhibits corresponding morphological change or taxonomic differentiation through time. Detailed comparisons of the Oreopithecus sample from Baccinello V-1 (and from the biostratigraphically equivalent sites of Ribolla, Casteani and Montemassi) with the type material of O. bambolii from the site of Monte Bamboli, tentatively correlated with Baccinello V-2, indicate that there are no morphological or metrical differences by which to distinguish them. The recovery of a small sample of Oreopithecus specimens from the Trasubbie River valley near Baccinello, derived from horizons stratigraphically above those yielding a V-1 fauna, allows, for the first time, direct comparisons of material from different strata within a single depositional basin. The material consists of a newly discovered partial mandible (IGF 4883V) from the F1 horizon, and four isolated teeth, a malar fragment, and a patella from the V-2 horizon. IGF 4883V is very similar to Oreopithecus specimens from Baccinello V-1, although it differs in having a more molariform P₃ and relatively larger cheek teeth. However, given the extent of variation in Oreopithecus, and the fact that the mandible almost certainly belonged to a male individual, these minor differences do not seem to be significant, and are best interpreted as being due to intraspecific variation. This conclusion is further supported by comparisons with Baccinello V-2 specimens, which appear to be indistinguishable from the large sample of specimens from Baccinello V-I. Although the sample of Oreopithecus specimens from horizons located above V-1 remains small, there is sufficient material to conclude that there is no evidence of morphological change or taxonomic differentiation in Oreopithecus during the time interval of about 2 Ma between Baccinello V-1 and V-2.