Solving a ‘puzzle’. The global 4.2 ka Bond Event at El Mirador cave (Sierra de Atapuerca, Burgos, Spain) and the importance of small mammal taphonomy to the interpretation of past environments and their climatic controls

Abstract

The regional climatic context in which Chalcolithic (MIR5) and Bronze Age (MIR4) levels from El Mirador cave (Sierra de Atapuerca, Burgos, Spain) are framed is affected by the 4.2 ka cal. BP event, a global event defined as a cooling and aridification phase. Previous works based on palaeoenvironmental inferences indicate conflicting results regarding the possible impact of the event on vegetation and small mammals from MIR5. Pollen record illustrates a possible aridification episode that could match with the 4.2 ka cal. BP event, while the signal of this event is not clearly recorded in the small mammal assemblage, which indicates more humid environmental conditions than pollen record. Taphonomic analyses confirmed that the small mammal assemblages from MIR4 and MIR5 are the result of predation, supporting the involvement of European eagle owls (Bubo bubo) in its formation. This avian raptor shows a marked preference for hunting animals living in the more open and wetter parts of their hunting range. Likewise, spontaneous specialisation on abundant prey species could also be observed under certain environmental conditions. This characteristic behaviour of eagle owls may have provided the contradictory results observed between the small mammal assemblage and palynological evidence. Nonetheless, taphonomic analyses also provided information about climatic conditions and fluctuations along time. The low incidence of manganese coatings and carbonate crusts deposits in small mammal bone remains from MIR5 support the presence of arid conditions during the formation of this level, which agreed with the aridification phase probably related to the 4.2 ka Bond Event inferred by palynological data from MIR5. These results provided a more robust conclusion about the paleoenvironmental contexts during the formation of Chalcolithic and Bronze Age levels at El Mirador cave.