The long paleoenvironmental sequence of Santimamiñe (Bizkaia, Spain): 20,000 years of small mammal record from the latest Late Pleistocene to the middle Holocene

The cave of Santimamiñe (Kortezubi, Bizkaia, Spain), on the southern slopes of the Ereñozar Mountain (Urdaibai biosphere reserve), is one of the most famous prehistoric localities of the Cantabrian range. Between 2004 and 2006, a test trench revealed a 6 m-deep stratigraphic sequence in the inner vestibule of the cave covering ∼20,000 years, from the latest Late Pleistocene (MIS 2) to the middle Holocene (MIS 1). It comprises six chrono-cultural units: lower, middle and upper Magdalenian, Azilian, Neolithic, and Chalcolithic/Bronze Age, plus seven lower purely palaeontological levels. More than 47,000 microvertebrate elements (including mammals, birds, reptiles, amphibians and fishes) were recovered, of which 1587 were identified to the genus and/or species levels. Of these, small mammals were used for paleoenvironmental reconstruction since they are very sensitive to climatic conditions and their distributions over time, measured in terms of relative abundance, serve as reliable proxies of habitat and climatic change. The reconstruction of Santimamiñe past environments based on small mammals roughly coincides with other proxies, such as the amphibian/reptile, large mammal/bird, palynological, and cryoclastic records on the local scale; other paleoenvironmental reconstructions from north Iberia on the regional scale; and the oxygen isotopic curve of an ice core from central Greenland on the global scale. All Magdalenian levels from Santimamiñe were deposited during the Oldest Dryas, a mostly cold and humid period including the Heinrich event 1. Small mammalian, palynological and cryoclastic evidence likely document the shift from the cold Younger Dryas to the beginning of the Holocene Climatic Optimum during Azilian times. The uppermost level, deposited during a moderate re-opening of the landscape at the Subboreal, slightly postdates the Holocene Cooling Event 3.