Abstract
Cainotheriids are a family of small artiodactyls, known in the fossil record from the late Eocene to the middle Miocene in Western Europe. Contrary to several European endemic ungulate groups that became extinct at the end of the Eocene or close to the Eocene–Oligocene transition (Grande Coupure), cainotheriids crossed this boundary and diversified during the Oligocene. The evolutionary history of cainotheriids around the Grande Coupure remains poorly documented and only a few works deal with the modalities of their evolution, notably because of the scarcity of available Eocene remains. A new fossiliferous karstic network named Dams was discovered during field prospecting in the Quercy area (Tarn-et-Garonne, France). It notably displays two infillings that yielded a great abundance of cainotheriid remains, namely DAM1 (MP19, late Eocene) and DAM3 (MP22, early Oligocene), bracketing the Eocene–Oligocene transition. A detailed study of cainotheriid mandibular and dental remains from these infillings reveals that only Paroxacron valdense occurs at DAM1, while five species are found in DAM3. The karstic network at Dams seemingly records a local taxonomic diversification of cainotheriids after the Grande Coupure, with Cainotheriinae being particularly successful. Our phylogenetic analysis, including cainotheriids from Dams, constitutes the first formal phylogeny of Cainotheriidae. Our results, based on mandibular and dental characters, allow us to (i) clarify relationships within Cainotheriidae, (ii) erect a new family Robiacinidae, as being the sister taxon to Cainotheriidae among Cainotherioidea, and, more broadly, (iii) discuss the controversial position of Cainotheriidae within Artiodactyla, as being more closely related to Ruminantia than to Tylopoda.