The return to the Iberian Peninsula: first Quaternary record of Muscardinus and a palaeogeographical overview of the genus in Europe

Although the earliest record of the genus Muscardinus dates from the Middle Miocene in Spain, no mention has been reported since the Lower Pliocene in the Iberian Peninsula. In this paper, Quaternary fossil remains of a hazel dormouse (Muscardinus avellanarius) are described, for the first time, in the Iberian Peninsula. These remains constitute the south-westernmost record of the genus in the Eurasian continent during the Late Pleistocene. The fossils, one first upper molar (M1) and two second upper molars (M2), come from Lezetxiki II Cave, an early Late Pleistocene site in northern Spain. The presence of the hazel dormouse agrees with the abundance of rodent species indicative of woodland, suggesting mild climatic conditions and a landscape formed by deciduous forest. This assemblage has been arguably assigned to warm and humid conditions related to an interstadial period in MIS 5. We also present an overview of the palaeogeography of the genus in Europe. The identification of this dormouse reinforces the idea of biological corridors between western Iberia and the rest of Europe during the Pleistocene.