New find of enigmatic pipid frogs in the Upper Pleistocene of the South American Pampas

BÁEZ, A.M.; GÓMEZ, R.O.; TAGLIORETTI, M.L.

Las Vegas

Congreso; Society of Vertebrate Paleontology 71th Annual Meeting; 2011

Society of Vertebrate Paleontology

Pipids are odd-looking frogs with a derived morphology that has been considered to be the result of a successful adaptation to a fully aquatic lifestyle. This monophyletic group comprises 33 extant species arranged in 3 clades mainly distributed in tropical regions of northern South America (Pipa) and sub-Saharan Africa (Xenopodinae and Hymenochirini). Their fossil record, however, documents greater diversity and wider distribution in South America in the Cretaceous and Paleogene. Recently, isolated postcranial bones bearing distinctive pipid features were discovered in an Upper Pleistocene locality in Argentina, nearly2000 km farther south from their present distribution in the continent. The recent find of a well-preserved ilium that might represent the same taxon in a Late Pleistocene locality of the Pampean Region confirms the intriguing presence of this group in southern South America. Comparisons with a broad sample of extant (Xenopus, 9 species; Pipa, 4 species; Hymenochirus, 1 species) and extinct (e.g., Avitabatrachus; Eoxenopoides; Saltenia; Shelania) pipids indicate that the Pleistocene material represents a new taxon. It is characterized by some presumably plesiomorphic features unknown in living taxa, such as the absence of dorsal crest and a moderate lateral exposure of the dorsal acetabular expansion. A preliminary phylogenetic analysis of pipoids combining morphological and molecular data places the new pipid as a stem xenopodine in an unresolved polytomy that also includes “Xenopus” romeri from the Upper Paleocene-Lower Eocene of Brazil as well as two taxa from the Eocene of Patagonia. The discovery indicates that stem-group xenopodines, once thought to have become extinct toward the end of the Eocene, survived in South America into the Quaternary implying an ample gap in the fossil record and posing interesting questions with regard to their evolutionary history. Finally, the available evidence is not sufficient to determine whether this archaic lineage survived in southern South America throughout this period or, conversely, whether it reoccupied higher latitudes from the north during an interglacial after their extinction in Patagonia.