The earliest known pipoid frog from South America: a new genus from the middle Cretaceous of Argentina

Abstract

ABSTRACT Vertebrate remains from the Late Albian–Early Cenomanian Candeleros Formation of northwestern Patagonia include those of a pipoid frog, which is described herein. The fossils consist of partially articulated and disarticulated elements, some of them badly broken, that are mostly exposed in ventral aspect. The description is based on one incomplete skeleton that presumably belongs to a single individual; this specimen possesses a combination of character states not present in other known non-palaeobatrachid pipimorph taxa and is identified here as a new genus and species, Avitabatrachus uliana. The species is moderately small (estimated snout-vent length ca. 35 mm) and shares with Pipidae conch-like squamosals, deeply excavated prootics to form channels for the Eustachian tubes, articulations for the lower jaws at the anterolateral corners of otic capsules, and fused sacrum and urostyle. Avitabatrachus possesses at least eight presacral vertebrae, the first two of which are fused, with flat, opisthocoelous centra. Unique features of this taxon are the presence of parasagittal flanges along the posterior halves of the otic capsules and the wide transverse processes of the posterior presacral vertebrae, which are only slightly anteriorly directed. Preliminary comparisons with other fossil pipoid taxa in the context of recent parsimony analyses suggest that it is the sister taxon of Pipidae. However, this phylogenetic placement of the new taxon should be corroborated in a future rigorous analysis that should include some putative stem pipid taxa that currently are being restudied.