The oldest articulated ranid from Europe: a Pelophylax specimen from the lowest Oligocene of Chartres-de-Bretagne (NW France)

Ranids represent an important part of the extant anuran diversity of Europe. One of the best-known genera is Pelophylax (green-water frog). This genus is considered to have arrived in Europe during the Eocene/Oligocene transition, with numerous occurrences of the genus throughout European Oligocene sites. Unfortunately, most of the specimens are isolated bones, hampering our understanding of the diversity and evolution of the genus during this time. We here present the description of an incomplete but articulated anuran skeleton from the lowest Oligocene of Chartres-de-Bretagne (western France). This specimen, missing its head, preserves almost all postcranial bones articulated and skin impressions. The osteological description allows to assign this specimen to Pelophylax kl. esculentus, making it one of the oldest known occurrences of the genus. We also suggest that specimens assigned to the late Oligocene "Rana" aquensis should be referred to the genus Pelophylax. The presence of a Pelophylax in western Europe during the early Oligocene indicates that the genus had already spread throughout Europe, no later than 5 Ma after its emergence in the eastern part of the continent. It suggests that Pelophylax benefitted from the extinction of ranoids during the "Grande Coupure."