Understanding the biogeography of Western European bats: the latest Pleistocene to Middle Holocene assemblage of El Mirador site (Sierra de Atapuerca, Spain)

The Lateglacial to Holocene transition is a key moment for understanding the extant configuration of bat populations in Western Europe, where several species are currently under threat. The Chiroptera fossil record for this period and region is poorly known. Here, we present the bat fossil record along the stratigraphical sequence of El Mirador (Burgos, North Spain), which ranges from the Late Pleistocene to the Late Holocene. Level MIR49 (11,396 to 8430 cal BP) has provided the richest bat assemblage from this chronology in the Iberian Peninsula. The 14 taxa identified conform a bat association with no extant equivalent, although all of them belong to the current Iberian fauna, evidencing a high biodiversity among the Iberian Early Holocene bat communities that had not been detected until now. The sibling species Myotis myotis and Myotis blythii appear together, showing the earliest clear evidence of the arrival of the eastern-coming M. blythii into Europe far West, probably related to the expansion of open environments during the Younger Dryas event. Conversely, the overlaying Middle Holocene section has provided low numbers of bats' remains. At El Mirador site, this impoverishment is more probably related to human presence than to climate fluctuations.