Sneaking past the Grande Coupure: diversity of snakes across the Eocene-Oligocene transition (MP 19-22) from Dams (Quercy, southwestern France)

The locality of Dams (Quercy, southwestern France) has yielded two distinct fossil assemblages, one from the late Eocene (MP 19) and a second from the early Oligocene (MP 22); it is one of the few examples of a locality with infillings across the Eocene-Oligocene transition. A minimum of 21 taxa (13 mammals, six lissamphibians) have been previously identified in Dams. Study of the snake ­remains from Dams yields two distinct assemblages, with a total of 11 taxa. The Eocene assemblage (five taxa) includes Eoanilius aff. europae, Platyspondylia sudrei Rage, 1988 and three constrictors, i.e., Palaeopython sp., “Palaeopython” neglectus Rochebrune, 1884 and an unnamed constrictor. The Oligocene assemblage (six taxa) includes Eoanilius aff. oligocenicus three unnamed alethinophidian species, two constrictors, i.e., Bavarioboa crocheti Szyndlar & Rage, 2003 and an unnamed ­constrictor species, and the caenophidian “Coluber” cf. cadurci. Among the 11 snake taxa from Dams, “Palaeopython” neglectus is identified for the first time from a precise locality and several unnamed Eocene and Oligocene alethinophidians are identified and described for the first time. The constrictor ­Bavarioboa Szyndlar & Schleich, 1993 is identified for the first time in the early Oligocene, pushing its appearance in the fossil record from the MP 25 back to MP 22. Comparison between the two assemblages highlights a complete turnover at the species level, with a single genus, Eoanilius Rage, 1974, present in both infillings.