PERSISTENT PRESENCE OF INTRIGUING PIPID FROGS IN THE PLEISTOCENE OF THE PAMPEAN REGION OF ARGENTINA

BÁEZ ANA MARÍA; TURAZZINI GUILLERMO F.; MARTINELLI AGUSTÍN; JOFRÉ GUILLERMO C.

Dallas

Congreso; Society of Vertebrate Paleontology 75th Annual Meeting; 2015

Society of Vertebrate Paleontology

In the last eight years paleontological prospection in several Pleistocene continental outcrops of the province of Buenos Aires has yielded disarticulated anuran bones ascribed to the ?archaeobatrachian? crown-group Pipidae, based on the distinctive morphology of these bones possibly related to aquatic adaptations. These records are remarkable owing to their geographical location, further south than the distribution of the living representatives in the continent, in lowlands of northern South America and eastern Panama. However, paleontological evidence demonstrates that the lineage represented today by Pipidae (i.e., Pipimorpha) reached central Patagonia in Late Cretaceous and Paleogene times. Herein we describe material recently collected in the upper Reconquista river basin, west of the city of Buenos Aires (34°41?S 58°48?W). The bearing beds have been referred to the Lower Green Luján Sequence, whose age range is 55-30 ka (OIS3). Previous records in the Pampean region are from mid Pleistocene (230-125 ka) beds of coastal cliffs (38°26?S 58°14?W) and late Lujanian (late Pleistocene) outcrops of central Buenos Aires province (36º44?S 61º45?W). In all these cases the remains consist of well-preserved but incomplete ilia and, occasionally, sacrourostylar complexes bearing a condyle for the articulation with the posterior-most presacral centrum. As in the previously described ilia, a dorsal crest is lacking along the preserved portion of the shaft, which represents more than 60% of its estimated total length, resembling the condition of known Cretaceous and early Tertiary pipimorphs but unlike the crested shafts of extant pipids. In having a well-developed dorsal prominence, reduced ventral and dorsal acetabular expansions in the acetabular plane, and relatively elongate acetabulum the ilium from the Reconquista river site conforms to those of pipids, but retains plesiomorphic features such as the longer than high dorsal prominence bearing an inconspicuous protuberance. The fragmentary sacrum is fused to the urostyle; it bears a tiny mid-dorsal ridge only between the flat articular facets of the elongate prezygapophyses unlike the living South American pipids. Although we were unable to determine the position of the taxon represented by these remains unambiguously, available data support their referral to a new pipid taxon. Pipids having archaic features, still undiscovered, may have persisted in more northern refugia, the Pleistocene rapid climatic changes probably causing latitudinal shifts and/or extinctions. Funded by PICT 1895/2011.