The late Neogene (the period between – 14 and – 2.4 Ma) is one of the most interesting phases in understand the present configuration of terrestrial ecosystems. It was during this time that the change took place from the middle Miocene dominant subtropical forests that stretched across southern Europe and western Asia to a more open but still wooded biotope that now prevails in warm–temperate areas. This change in vegetation, which strongly affected the composition of mammalian faunas, seems to be linked to the rapid spread of grasses around 8–10 Ma ago. Moreover, in the late Neogene, climatic shifts and falling temperatures due to the spread of the Antarctic Ice, were followed by the Plio-Pleistocene Arctic glaciations in the Northern Hemisphere. Furthermore, during the late Neogene, important changes at the regional level gave rise to the present configuration of the Old World land masses, and the successive drying of inland seas in the European area facilitated faunal interchange between Europe and Central Asia and Africa. At the same time, other tectonic processes like the Himalayan and the Tibetan uplifts and the opening up of the great eastern African basins and Red Sea, although working in opposite directions, favoured the processes of speciation and isolated evolution.

All these phenomena must have had a strong influence on hominid evolution between 14 and 2 million years ago (Ma). The diversity of hominid species recorded in that period must be considered in relation to the changing environmental conditions and to constrictions imposed by the existence of significant zoogeographical barriers.

Introduction

The global climatic events detected from 12 to 7 Ma include changes in the atmospheric and oceanic circulation, and increasing latitudinal gradients of temperature, starting with the extensive Antarctic glaciation (Miller et al., 1991; Wright et al., 1992; Keller & Barron, 1983) and the beginning of minor glacial processes in the Arctic regions (Zubakov & Borzenkova, 1990). Late Miocene mammal turnovers have often been regarded as being logically induced by this set of changes in the global climate (Steininger et al., 1985; Barry et al., 1985; Meulen & Daams, 1992). This is especially true in the case of hominid evolution, in which extension of dry environmental conditions over large areas of Eurasia and Africa has been regarded as a major feature (Coppens, 1983; Vrba et al., 1997). However, in several cases this is not based on long terrestrial stratigraphic sections with good chronological control but rather on assumed biochronologic correlations not directly supported by an accurate, reliable stratigraphic framework (with the noticeable exception of the work developed in the the Potwar Plateau by the ‘Siwaliks team’; see Barry et al., 1985; Barry & Flynn, 1990; Morgan et al., 1994; Pilbeam et al., 1996). The recently developed magnetostratigraphic and biostratigraphic framework in the Vallès-Penedès Basin (NE Spain) allows, for the first time, a close comparison between the middle–late Miocene mammalian record of Western Mediterranean and Central Asia areas (Figs. 20.1 and 20.2) and its long distance correlation with the global events detected in the oceanic record (Miller et al., 1991; Wright et al., 1992; Flower & Kennett, 1994).

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.