Relative size variations of Microtus arvalis and Microtus agrestis as climatic proxy: the case of Grotta Fumane

Fumane cave (350 m a.s.l.) is located in the Veneto Pre-Alps, north-eastern Italy. It presents one of the most important and well-dated palaeolithic sequence of Late Pleistocene of the Italian Peninsula. In this study, we analysed the relative size variations of the first lower molar of Microtus arvalis and Microtus agrestis during Marine Isotope Stages (MIS) 3-2, quantifying these variations with the Lagr/Larv index. We compared our results with previous studies of climatic and environmental reconstructions based on small mammals and with previous studies on large mammals and birds , in order to investigate the efficacy of the index as proxy for climatic oscillations through the sequence of the site. We observed that, while Microtus arvalis showed an increase in size during arid periods, Microtus agrestis became larger during humid pulses. The Lagr/Larv index proved to be an excellent indicator of the general level of humidity in the surrounding of Fumane cave (presence/absence of surface water resources, increase/decrease of open humid environment), although it is not directly correlated with the mean annual precipitation calculated for the sites but probably related to the annual distribution of rainfalls. Comparing the values of the Lagr/Larv index of Fumane cave with those of other sites of the Italian Peninsula, northern Iberian Peninsula, Croatia, Hungary and Belgium, we analysed the responses of the two species to the climatic oscillations of MIS 3 and MIS 2 in different geographic and climatic areas.