Abstract
Cainotheriidae are small artiodactyls restricted to Western Europe deposits from the late Eocene to the middle Miocene. From their first occurrence in the fossil record, cainotheriids show a highly derived molar morphology compared to other endemic European artiodactyls, called the "Cainotherium plan", and the modalities of the emergence of this family are still poorly understood. Cainotherioid dental material from the Quercy area (Palembert, France; MP18-MP19) is described in this work and referred to Oxacron courtoisii and to a new "cainotherioid" species. The latter shows an intermediate morphology between the "robiacinid" and the "derived cainotheriid" types. This allows for a better understanding of the evolution of the dental pattern of cainotheriids, and identifies the enlargement and lingual migration of the paraconule of the upper molars as a key driver. A phylogenetic analysis, based on dental characters, retrieves the new taxon as the sister group to the clade including Cainotheriinae and Oxacroninae. The new taxon represents the earliest offshoot of Cainotheriidae.