Résumé
Herpetotheriidae are small extinct stem-marsupials with a superficially “opossum-like” dentition.Here, we shed light on three crucial phases of their previously obscure European evolutionary history.(i) Each metatherian family known in Europe likely dispersed once from North America (Gernelle et al.2024). We report the earliest unequivocal herpetotheriid from a French locality that slightly predatesthe Paleocene-Eocene Thermal Maximum (PETM). This new genus and species is the smallestEuropean herpetotheriid known so far and probably represents a case of mammalian dwarfism priorto the PETM. (ii) All early Eocene metatherian species from Western Europe then rapidly becameubiquitous in this part of the continent, contrary to most eutherian ones. In parallel, relativelylarge species such as Peratherium musivum and Peratherium maximum appear. We illustrate theimportance of studying changes in molar cusp – basin proportions and correlated characters thatoccurred during the evolution of these larger herpetotheriids. This leads us to hypothesize differentdiets for Eocene European metatherians than those initially inferred using Messel individuals, suchas Peratherium aff. maximum (Gernelle et al. 2025). (iii) New phylogenetic analyses suggest thatthe enigmatic Anatoliadelphyidae from the middle Eocene of the insular Pontide terrane (Anatolia)fauna are derived from a European herpetotheriid stock, rather than South American emigrants.Because anatoliadelphyids were larger and probably durophagous compared with herpetotheriids,a promising approach to clarify the herpetotheriid origin of anatoliadelphyids would be to restudythe older Peratherium aff. maximum from Messel and Geiseltal. This taxon displays unusuallylarge carnassial teeth for a herpetotheriid, which is a functionally relevant diagnostic characterin anatoliadelphyids. Altogether, the typically dentally conservative herpetotheriids underwentmorphological diversification while increasing in size, likely following niche invasions during earlyto middle Eocene.