New Clues on Anuran Evolution: The Oldest Record of an Extant Hyloid Clade in the Oligocene of Patagonia

Abstract

Despite the enormous diversity of the extant South American batrachofauna, its fossil record is sparse.Few pre-Neogene anuran remains have been attributed to extant taxa and, although some have been considered neobatrachians their relationships with extant groups are still mostly uncertain. In thiscontext, a series of fossils recently collected in Oligocene sediments of central Patagonia are assigned to Odontophrynidae. This assignation is supported by an exclusive combination of characters, including extensive frontoparietals, in medial contact and deflecting posteriorly, with crescent-shaped posterolateral projections; robust pterygoid anterior ramus, reaching the planum antorbitale, projecting dorsally; notched premaxillary pars palatine; dentate vomers, narrowly separated medially; robust neopalatines, narrowly separated medially, bearing a conspicuous ridge, and with expanded lateral edges. The well-preserved fossil specimens were considered representative of a new genus and species, Chachaiphrynus lynchi. The presence of an Oligocene Odontophrynidae in central Patagonia, about 500 km south from the southernmost extant distribution of the group, would be associated with the more benign climate inferred in this region during the Paleogene. At the same time, this record represents the single pre-Neogene certain record of an extant clade deeply nested in Hyloidea, providing an exceptional high-quality calibrationpoint to temporally frame the anuran phylogeny.