Palaeoenvironmental research at Rexidora Cave: New evidence of cold and dry conditions in NW Iberia during MIS 3

Abstract

The Rexidora Cave (Asturias, NW Spain), discovered in 2012, provided a remarkable large mammal assemblage of MIS 3 age. The ongoing excavation works yielded 445 fossil remains including cold-adapted elements as woolly rhinoceros (Coelodonta antiquitatis) and reindeer (Rangifer tarandus), two species of special interest since they are poorly represented in the Iberian Pleistocene. The woolly rhinoceros assemblage comprises numerous unusually well preserved elements as one mandible, one femur and one partially preserved skull. The steppe bison (Bison priscus) is the dominant species in the assemblage, providing an outstanding collection of well-preserved elements that comprises two skulls and numerous limb bones. Carnivores are represented by a partial skeleton (including a complete skull) of spotted hyena (Crocuta crocuta).Radiocarbon AMS analyses of the fossil assemblage yielded two dates of 44.5 and 37.6 Cal ka BP, corresponding to MIS 3, a phase of climatic instability characterized by fast climate changes, from extreme cold to temperate conditions. These dates are coeval with the maximum registered expansion of the mammoth fauna in the Iberian Peninsula and with the onset of glacier retreat in the Cantabrian Mountain Range, after the last local glacial maximum.Geomorphological and sedimentological evidence suggests that bone accumulation took place as the result of gravity processes in a collapse doline, filled by a chaotic accumulation of calcareous boulders, pebbles and bone fragments, embedded in a silt–clay matrix, which points to a possible natural-trap origin of this fossil assemblage. The exceptional well preservation of the fossils, as well as the lack of any evidence of human or carnivore activity, supports this idea.Palynological analyses suggest an open landscape under variable climatic conditions, responsible for the fluctuating presence/absence of the arboreal taxa. The predominance of steppe and, to a lesser extent, xeric herbaceous plants indicate very dry conditions, whereas presence of mesophilous forest taxa implies the existence of a refuge area at distance. This open and dry landscape, developed in a karst area with a relative smooth relief, is consistent with the occurrence of the large mammal species steppe bison, woolly rhinoceros and reindeer. Faunal and pollen analyses, hence, provides a new evidence for the development of cold and dry steppe-like environments in NW Iberia during MIS 3.