New Earliest Palaeotheriidae (mammalia, Perissodactyla) from the Ypresian of Southern France: Phylogeny and Diversification in a Hyper-Thermal Context

A new Ypresian locality from southern France, St-Eulalie 3, located in the Minervois Basin (Hérault, France), near the locality St-Eulalie -the type locality of the primitive palaeothere, Pachynolphuseulaliensis has yielded additional specimens attributable to this species. The morphological similarity between this material and several specimens previously described from the nearby Ypresian locality of La Borie (Lauragais, Aude, France), prompted us to also examine recently excavated material from that site. Both St-Eulalie localities and La Borie are assigned to the MP8+9 European Palaeogene mammalian reference level. Furthermore, the two St-Eulalie localities are proposed to fall within the ETM3 hyperthermal event (52.845 Ma), providing a crucial temporal framework for documenting early palaeothere diversification within a well-constrained climatic context. In addition, the three studied populations exhibit considerable dental variability, particularly on the upper premolars. The comparison of well-preserved crania allows a refined diagnosis of the species and the identification of dimorphic traits. Finally, this study presents a new phylogenetic analysis that supports the monophyly of Palaeotheriidae in their sensu lato topology, including the paraphyletic pachynolophs. Pachynolphus eulaliensis represents the earliest diverging taxa within the family, the latter estimated to have diverged between the PETM (MP7) and the ETM3.