Anatomy and phylogeny of an exceptionally large sebecid (Crocodylomorpha) from the middle Eocene of southern France

Post Cretaceous–Paleogene (K–Pg) boundary continental ecosystems of Europe host a distinctive assemblage of derived neosuchians related to modern semi-aquatic lineages, including the alligatoroid Diplocynodon and the crocodyloid Asiatosuchus but also a less well-understood group known as the Planocraniidae. Yet, uniquely in its faunal composition, Europe also preserves some of the last representatives of Notosuchia, a group that previously underwent a successful radiation in terrestrial ecosystems of the Cretaceous, especially in Gondwana. Although Europe harbored a few members of Sebecosuchia during the Cretaceous, their affinities with post-K–Pg forms is not ascertained, in part due to their rare and fragmentary nature on both sides of the stratigraphic boundary. Paleogene European sebecosuchians have been reported from the Eocene of France, Germany, Portugal, and Spain. Resolving their phylogenetic position may shed light on their suspected Gondwanan affinities. Based on new cranial and postcranial remains, we provide a description of the most complete and largest European sebecosuchian to date from the middle Eocene (Bartonian) of Issel and Réalmont, southern France. Dentaneosuchus gen. nov. is proposed to designate the taxon originally described as Atacisaurus crassiproratus. A phylogenetic analysis recovers Dentaneosuchus crassiproratus as the basalmost branching member of Sebecidae, a clade otherwise known from abundant specimens from the Paleogene and Miocene of South America. Among post-K–Pg sebecids, Dentaneosuchus crassiproratus rivalled in size with Barinasuchus arveloi from the Miocene of Venezuela, demonstrating that sebecids achieved the status of apex predators in terrestrial ecosystems of both Europe and South America.