New endemic large mammals from the Lower Miocene of Oschiri (Sardinia): Observations on evolution in insular environment

Abstract

The Oschiri fauna is the oldest endemic insular fauna known from the Mediterranean and one of the oldest worldwide. It presents a rare opportunity to study the effects of insular ecology on the evolution on more primitive relatives of the typical Quaternary endemics. The following macromammals are described: Hyotherium? insularis n.sp. (Artiodactyla, Suiformes, Suidae, Hyotheriinae), Bachitherium sardus n.sp. (Ruminantia, Bachitheriidae), “ Amphitragulus” sp. (currently placed in Palaeomerycidae), Moschidae? indet., Sardomeryx oschiriensis n.gen. n.sp. (Giraffoidea?), and possibly a perissodactyl. The large mammals from Oschiri may have arrived during unit MN3 (corresponding to the Ramblian, Burdigalian or Early Miocene), or some 20 Ma ago. The composition of the whole fauna resembles that of the Quaternary Mediterranean islands. The abundance of ruminants, even if belonging to different families, resembles the situation in Quaternary insular faunas, which tend to be dominated by Cervidae (Crete, Ryukyu islands) and Bovidae (Balearics). Apparently, Ruminantia are good colonisers of islands and good competitors in insular environment. The ruminant families and suid subfamily that are reported for the first time as insular endemics, show similar adaptations as found in the Quaternary endemics. These observations support the idea that, insular ecologies result in convergent evolution, independent of the geological age or taxonomic composition of the initial fauna.