Changes in the macromammal richness of Spain during the Neogene

Abstract

Abundance and composition of Iberian macromammal faunas has suffered important changes during the Neogene (23 to 2 million years before present). The present paper analizes and describes these changes, also disccusing the taxa involved and their possible causes. Results from the present study point out the existence of an increase in the Iberian species richness from the end of the Lower Miocene to the first half of the Upper Miocene, followed by an strong impoverishment from then on till the Pliocene, interrupted by a temporal increase during the end of the Miocene. Local faunas (individual localities) from the Middle and Upper Miocene are, in some cases, exceptionally diverse, comparable to the richest extant tropical ecosystems. Diversity changes in time are usually explained as a response to climatic changes. However, our analyses point out that many of the observad changes in diversity may be due to differences in the fossil record quality. At locality (local) level caused by differences in the processes of locality formation, while at regional scale due to the number of deposits recently published global climate curves for the Neogene as well as with the up to date biogeographic knowledge, shows that diversity changes appear to be most closely related with the open and close of biogeographic barriers and to a lesser degree of variation in the global levels of CO₂ concentration. Our results also show different relationship between local (number of species per site) and regional (number of species in the whole Iberian Peninsula) diversity that could be due to changes in the environmental heterogeneity of the Iberian Peninsula along the time considered.