Revision of a classic site for Permian tetrapod ichnology (Collio Formation, Trompia and Caffaro Valleys, N. Italy), new evidences for the radiation of captorhinomorph footprints

The recent studies on Permian captorhinomorph (non-diapsid eureptile) footprints from North America, North Africa, and Europe raised the interest on their taxonomic and biostratigraphic significance. They seem to radiate in the late Early Permian, but the scarcity of absolute dating in the classic sections bearing these trace fossils is not helpful in order to unravel their distribution. The continental Collio Formation cropping out extensively in the central Southern Alps of Italy can cover this gap of knowledge, since it preserves a rich testimony of these trace fossils (Erpetopus, Hyloidichnus, Varanopus) and it is well-constrained from radiometric datings and fossil content. For this and because of the huge amount of stored but unanalyzed material, a revision was necessary, through careful taxonomic assignations. These taxa are here confirmed and/or identified as being: Amphisauropus kablikae, cf. Batrachichnus isp., Dromopus lacertoides, Erpetopus cassinisi, Hyloidichnus bifurcatus, Limnopus heterodactylus and Varanopus isp. The occurrence of Erpetopus at the base of the Collio Formation (Kungurian base) suggests its minimum age of first appearance in a global context: this is a very important presence in order to build a reliable tetrapod footprint biostratigraphy during the Permian. The quantity of material yielded in the different facies of the Collio and Dosso dei Galli Formations also permit new insights on the paleoenvironments and climatic settings.