Introduction

The MN mammalian biochronological classification of the European terrestrial record has been the subject of intensive criticism since its first formulation by Mein (1975). More than twenty years later, the question of its validity is still open, although, unlike previous times, we now have ways for falsifying this ‘hypothesis of mammalian succession’ (as it was defined by Agustí & Moyà-Solà, 1991). Originally, the MN ‘zonation’ (as it was sometimes wrongly quoted) reflected a pattern of mammalian turnover in the European terrestrial record, mainly based on supposed large overland dispersals and extinctions. To these two criteria, Mein (1975) also added the successive chronospecies of several European mammalian lineages (mainly rodents) as a third criterion for establishing the MN units. Agustí & Moyà-Solà (1991) proposed a restrictive interpretation of the MN units as a regional, Western European mammal scale based on the stratotypical succession of the Neogene mammal stages defined in a number of Spanish basins (by far, the most complete Neogene succession in Western Europe). A very different approach was that of a reinvented ‘RCMNS working group’ (Bruijn et al., 1992), which proposed to avoid completely the assumed biostratigraphic meaning of the MN units, and to redefine them on the basis of reference-levels, returning to the system proposed in the 1960s by Thaler (1966), and that the Mein (1975) proposal was supposed to surpass. Each MN unit being defined only by an isolated reference-locality, this system remained as a selfish way for paleomammalogists to classify their fossiliferous localities within an assumed chronological background, but without any possibility of falsification or correlation with other biostratigraphic scales, given the absence of a true biostratigraphical background.