A late Eocene frog assemblage from the Geste Formation, Puna of north-western Argentina

Frogs (Anura) are major components of tetrapod communities in the Neotropics and, according to divergence-time estimates, were already diverse in early Palaeogene times, but this is still poorly documented in the fossil record. A late Eocene frog assemblage from the Geste Formation exposed at Antofagasta de la Sierra (Catamarca province) is here described, providing a first glimpse into the Palaeogene anuran diversity in the present-day Puna of north-western Argentina. The assemblage is composed by at least four hyloid neobatrachian taxa having miniature to large body-sizes, ranging 17-81 mm estimated snout-vent length. Neither the families currently found in the Puna-Altiplano, nor those from the Cretaceous - Eocene of southern South America, are represented. The assemblage comprises possible brachycephaloids, odontophrynids, and hemiphractids, suggesting climatic and environmental conditions very different from the harsh conditions prevailing today in the Puna-Altiplano and a biogeographical link with Amazonia. The joint presence of these taxa is currently restricted to the nearby Austral Yungas and the Atlantic Forest, suggesting that the late Eocene frogs likely inhabited a humid forest. The new frog assemblage constitutes a rare window to the early evolution of Neotropical anurans and a major leap forward in the palaeoenvironmental reconstruction of the Puna during Eocene times.