Reconstruction of the Late Miocene climate of Spain using rodent palaeocommunity successions: an application of end-member modelling

End-member modelling is applied to a data set of relative abundances of 67 Upper Miocene rodent associations (11–6 Ma) from Spain, France, Austria and Greece. The analysis results in the robust estimation of relative levels of four climatic parameters: humidity, temperature, seasonality type and predictability. In the preparatory stage, species are aggregated into nine groups on the basis of ecological criteria. Humidity preferences and adaptations are based on actualistic and functional morphological interpretations of dentition and locomotion. Temperature preferences are inferred from palaeobiogeographic distributions. Levels of adaptation to seasonality type (wet–dry or cool–warm seasonality) are assigned on the basis of diversities in present-day climate/vegetation zones, and the ability of extant relatives to hibernate. Demographic data are used to formulate adaptations to climatic (un)predictability. In the modelling stage, the compositions are unmixed into the contributions of four end members. These four extreme, theoretical rodent compositions are interpreted in climatic terms, and their contributions to the samples are used for the estimation of climatic parameters. The subset of 44 well-dated rodent compositions from the Calatayud-Daroca and Teruel basins (NE Spain) is used to construct detailed climatic curves for the Late Miocene, while the geographical dimension in the data set is used to calculate inter-basinal differences. The model results for Spain indicate more humid and cooler conditions between 10.5 and 8.5 Ma, around 7, and around 6 Ma, and more arid and warmer conditions before 10.5, between 8.6 and 7.5 Ma and around 6.5 Ma. Superimposed on this pattern is a shift from a more predictable, cool–warm seasonal climate towards a more unpredictable, wet–dry seasonal climate between 9.4 and 8.2 Ma. Inter-basinal comparisons per time slice show that the climate in southern Europe was dryer, warmer, more wet–dry seasonal and more unpredictable than in central Europe, and that the climatic and vegetational boundaries between the two regions were sharp. The occurrences of more humid and cooler episodes in Spain during the Late Miocene might be explained by southward migrations of the boundary between a temperate and subtropical-dry climatic belt and their associated vegetation types. Various positive correlations are observed between the rodent-based climatic curves for Spain, and other palaeoclimatic records from the Mediterranean and NE Atlantic region (clay minerals, marine fauna, stable isotopes). The two cooling maxima at 9.4 and 7 Ma closely correspond to clusters of marine events which are generally considered to reflect maxima of global ice volume.