First Eocene lizard (Squamata) from Balkanatolia documents overwater dispersal of Paleogene pleurodontan iguanians.

We here describe a fossil jaw fragment from the middle Eocene (Lutetian) Uzunçarşıdere Formation in Anatolia, pertaining to a pleurodontan iguanian. This region during most of the Eocene was part of an isolated insular landmass, called Balkanatolia, that is mostly known for its peculiar and diverse insular mammalian fauna. The lizard specimen represents the first evidence of Eocene reptiles from Balkanatolia, providing a first glimpse into the herpetofaunas of this, now lost, insular landmass. The fossil material is rather fragmentary, precluding a more precise identification, but its distinctive tooth morphology confirms the presence of pleurodontan iguanians in the region for the first time. The presence of a distinct mesiodistal groove along the apical crest of the central cusp in the teeth of the Anatolian pleurodontan is of particular interest, as this feature is otherwise observed only in the Eocene genera Cadurciguana from Western Europe and Parasauromalus from North America, plus the extant American lineages of Dactyloidae, Leiocephalidae, and Polychrotidae. Interestingly, this feature seems to be absent from all other pleurodontans, including the abundant Eocene corytophanid Geiseltaliellus. The new find indicates another successful overseas dispersal of pleurodontans, a group that has repeatedly colonized distant landmasses, including oceanic islands, throughout its evolutionary history. Taking into consideration the diversity and abundance of pleurodontans in the Eocene of Europe and the total absence of the group from coeval Africa and Asia, it is likely that the new Anatolian iguana arrived from the former continent sometime between the early and early middle Eocene.