A review on the Late Villafranchian medium-sized canid Canis arnensis based on the evidence from Poggio Rosso (Tuscany, Italy)

The fossil canid material recovered from the Early Pleistocene site of Poggio Rosso offers the opportunity to revise the taxonomical status of the Arno River dog, Canis arnensis. To date, the identification of this species is still a matter of debate due, on the one hand, to the poor state of preservation of the type specimens, and on the other hand to the lack of homogeneous descriptions and a clear diagnosis. The fossils recovered from Poggio Rosso show a good state of preservation with little (if any) plastic deformation, allowing re-evaluation of the dental and cranial characters typical of this species, as well as the proposal, for the first time, of a precise and specific diagnosis. The anatomical and morphometric features of C. arnensis exclude a close taxonomical relationship with the coeval Canis etruscus, suggesting instead a closer affinity to modern canids. The C. arnensis arrived in Italy around 1.9 Ma as the result of a dispersal event, and Poggio Rosso is the first Italian site recording the occurrence of this species. The dispersal of C. arnensis represents the arrival of the first modern canids in Europe and is therefore a significantly important biochronological event in European faunal assemblages.