Résumé
One of the main focuses of evolutionary biology studies today is investigating the evolutionary and ecological processes responsible for the diversification and decline of clades. The ‘Grande Coupure’ corresponds to a major turnover in the European fauna during the severe biological and climatic crisis of the Eocene–Oligocene transition (EOT), 33.9 million years ago (Ma). In Western Europe, this biological event is characterized by the dramatic extinction of insular European mammals, coupled with the massive arrival of modern Asian clades. Several hypotheses have been proposed to explain this extinction, including abiotic factors such as temperature, sea level, and seasonality, as well as biotic factors such as competitive interactions. However, these hypotheses have never been formally tested. Here, we examined the diversification of Western European mammals to determine the primary drivers of the Grande Coupure and to understand how the modern mammal fauna became established in Western Europe 34 Ma. Using Bayesian birth-death models considering the preservation bias of the fossil record, we analyzed a high-resolution fossil occurrence dataset (578 species, >3,300 occurrences) from Southern France spanning the late Eocene-Oligocene interval and estimated the regional diversification and diversity dynamics of endemic and immigrant European mammals. Our results show that a combination of multiple abiotic factors played a significant role in the diversification of European endemic mammals and that the major environmental changes at the EOT were responsible for the extinction of 65% of species. Importantly, our results do not support the hypothesis of competitive interactions between endemic and immigrant taxa. Instead, our results suggest that immigrant species opportunistically replaced endemic species after the EOT by colonizing new ecological niches left vacant. Interestingly, the diversity recovery of European mammals during the early Oligocene was not rapid, but occurred over three million years, indicating a gradual arrival of immigrant mammals in multiple migratory waves.