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 o f four climatic parameters: humidity, temperature, seasonality type and pre dictability. in the preparatory stage, species are aggregated into nine gro ups on the basis of ecological criteria. Humidity preferences and adaptatio ns are based on actualistic and functional morphological interpretations of dentition and locomotion. Temperature preferences are inferred from palaeo biogeographic distributions. Levels of adaptation to seasonality type (wet- dry or cool-warm seasonality) are assigned on the basis of diversities in p resent-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 in to the contributions of four end members. These four extreme, theoretical r odent compositions are interpreted in climatic terms, and their contributio ns to the samples are used for the estimation of climatic parameters. The s ubset of 44 well-dated rodent compositions from the Calatayud-Daroca and Te ruel basins (NE Spain) is used to construct detailed climatic curves for th e 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 aro und 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 mo re predictable, cool-warm seasonal climate towards a more unpredictable, we t-dry seasonal climate between 9.4 and 8.2 Ma. Inter-basinal comparisons pe r time slice show that the climate in southern Europe was dryer, wanner, mo re wet-dry seasonal and more unpredictable than in central Europe, and that the climatic and vegetational boundaries between the two regions were shar p. The occurrences of more humid and cooler episodes in Spain during the La te Miocene might be explained by southward migrations of the boundary betwe en a temperate and subtropical-dry climatic belt and their associated veget ation 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 i sotopes). The two cooling maxima at 9.4 and 7 Ma closely correspond to clus ters of marine events which are generally considered to reflect maxima of g lobal ice volume. (C) 1999 Elsevier Science B.V. All rights reserved.