Résumé
A new Eocene locality in southern France has yielded a poorly diversified vertebrate fauna but does contain abundant material representing a new species of early equoid, Pachynolophus eulaliensis, sp. nov. Biostratigraphic data for this new locality of Sainte-Eulalie suggest a middle Ypresian age. The new species is the oldest representative of the Palacotheriidae, here including the controversial pachynolophs. The abundant remains of this taxon from a single locality allow the recognition of a high degree of unsuspected variability within this taxon, including sexual dimorphism, thus permitting discussion of the reliability of commonly used characters. A phylogenetic analysis led us to emend the diagnosis of the genus Pachynolophus as well as to suggest the exclusion of ‘Pachynolophus’ hookeri from the genus. This study proposes new hypotheses of relationships among the basal Equoidea and allows us to distinguish the two main groups (Equidae and Palaeotheriidae) earlier in the Eocene, close to the reference level MP8–9. The new material appears to be a fundamental cornerstone in solving the question of the controversial systematics and phylogeny of pachynolophs. It also sheds new light on the temporal and spatial distribution of the initial radiation of European equoids.