Updated biochronology of the Madrid Basin: species distribution and implications for the Middle Miocene rodent faunas of Spain

The works carried out in the Madrid area during the last fifteen years have yielded almost twenty new localities including small-mammals. A taxonomical description of the rodent fauna of the new sites and a revision of those previously published has enabled us to present an updated biostratigraphy and biochronology for the middle and upper Aragonian of the Madrid Basin. Seven local biozones are recognised: Db, Dc, Dd, E, F, G1 and G2. The rodent assemblage of biozone Db is here described for the first time in Madrid. The new finds have also filled poorly-known parts of biozones Dc, Dd, E and F, making now the rodent assemblages of biozones Dc and E from Madrid one of the most complete and best-represented records. Considering the faunal variability in biozone G1 in the Madrid Basin, we propose a new definition for it. The comparison of the rodent assemblages between the Madrid and Calatayud-Montalbán basins points out that both share several similarities in their taxonomical distributions, although with less diverse faunas in Madrid. A relative impoverishment in taxa of complicated dental pattern in Madrid could be interpreted as due to differences in the local environment with Calatayud.