Insights into the Extinction of the Palaeotheres (perissodactyla; Mammalia): Paleoecological Inferences from Southeastern France

Palaeotheres are an extinct family of equoids (Perissodactyla; Mammalia) from Eurasia that lived from the Middle Eocene to the Early Oligocene. Although very abundant and prosperous during the Eocene, most palaeotheres became extinct during the “Grande Coupure” (33.9 to 33.4 Mya), a major biological crisis marking the transition from the Eocene to the Oligocene. Two main causes have been suggested to explain this faunal turnover: •the deterioration of climatic conditions, due to a drop in pCO2 responsible for the Terminal Eocene Event (~ 33.9 Mya) – an abrupt cooling of about 4 to 6°C – and a glaciation during the Oi-1 event (~ 33.5 Mya), resulting in drier and more open habitats during the Early Oligocene; •the immigration of Asiatic taxa via new continental bridges following a drop in global eustatic sea level caused by the cooling event. These immigrations marked the end of the insular context of Europe (middle and late Eocene) and of the associated endemism. Competition with newcomers is often cited as the cause of the extinction of endemic European taxa, such as palaeotheres. However, recent studies on artiodactyls in Quercy (southwestern France) have challenged this view, and suggested a passive replacement of endemic European taxa by newcomers from Asian, better adapted to the new environmental conditions. Here, we studied the palaeotheres species from two fossil sites in southeastern France, Euzet-les-Bains (MP17; -37 Ma) and La Débruge (MP18; -35.5 Ma), at which seven and nine palaeotheres species have been identified respectively. We used a multi-proxy approach based on dental material to evaluate body mass, stress levels (enamel hypoplasia), dietary and habitat preferences (dental micro- and meso- wear, δ13C and δ18O) of these palaeotheres species. The results suggest a large range of body masses (10 to 1000 kg) and various browsing diets (little overlap in the dental wear signals), although all in the C3 range, for the studied palaeotheres. Moreover, the prevalence of hypoplasia was really low, i.e. < 2 % for most taxa at both localities, indicating a context of low physiological stresses. This was probably due to favorable environmental conditions, warm (MAT: 17-20 °C) and humid (MAP: 1200-1300 mm/year) as reconstructed by stable isotopes, and low competition for resources, as suggested by dental wear and carbon isotopes. This research is part of the PIPE project funded by the Swiss National Science Foundation n°10.001.379