Insular aurochs (Mammalia, Bovidae) from the Pleistocene of Kythera Island, Greece

Islands are renowned for their remarkable biotas and have been widely recognised as natural laboratories for the study of evolution, speciation, and extinction. Large mammals in insular environments typically evolve to dwarfs and small ones to giants, a trend known as the island rule. Despite their dominance in the continental European mammal faunas of Middle-Late Pleistocene, Bison and Bos are usually lacking from the neighbouring endemic insular assemblages. Here, we report the first insular bovin from the Late Pleistocene of Kythera Island, Greece and we carry out a detailed morphometrical analysis with emphasis on its adaptations and palaeogeographic implications. Based on both dental and postcranial qualitative and quantitative comparisons, we attribute the studied material from Kythera to Bos primigenius. Significant differences from both its continental Pleistocene relative and the endemic bovins from Mediterranean islands, allow us to recognize it as a new subspecies, Bos primigenius thrinacius n. ssp., the third known insular dwarf of this taxon in Europe. Our main hypothesis is that the gradual disconnection of Kythera Island from the neighbouring Peloponnese peninsula just after MIS 6 (late Middle Pleistocene, ∼180 ka) resulted in the isolation of a mainland Bos primigenius population in the rocky and predator free environment of palaeo-Kythera Island. Under these particular conditions the population underwent some remarkable changes and gained some peculiar features, especially on metapodials. The timing and reasons of Bos primigenius thrinacius extinction remain unknown. •Description of the first insular auroch from the Late Pleistocene of Greece.•Definition of a new auroch subspecies, representing an insular dwarf.•Morphometrical comparison of insular bovins from Mediterranean.•Discussion of evolutionary trends of aurochs on islands.•Palaeoographic evolution of Kythera Island during the Late Pleistocene.