Redescription of the Paleogene Shelania pascuali from Patagonia and Its Bearing on the Relationships of Fossil and Recent Pipoid Frogs

Abstract

Shdania pascuali Casamiquela, 1960, is redescribed on the basis of a series of 30 recently discovered specimens, which range in estimated snout-vent length from 30-100 mm, from the Paleogene of Patagonia. This large pipoid anuran is distinguished by possessing a long, narrow braincase; an hourglass-shaped frontoparietal; a robust antorbital process on the edentate maxilla; long, straight ilia that describe a V-shape in dorsal profile; and a trunk that is long relative to the lengths of the head and limbs. A phylogenetic analysis of 11 fossil and Recent pipoid taxa based on 51 osteological characters resulted in three equally most-parsimonious trees of 84 steps. In each arrangement, rhinophrynids and palaeobatrachids are successive sister groups to a clade composed of Saltenia, Shelania, Eoxeiiopoides, "Xenopus" romeri, xenopodines, and pipines. "Xenopus" romeri always clusters as a stem taxon with the xenopodines, as does Eoxenopoides with the pipines. The phylogenetic positions of Shelania and Saltenia remain unresolved. In two of the trees, these taxa are sister to the clade comprising the re- maining pipid taxa—either forming a clade or as successive sister taxa; in the other tree, Shelania is the sister taxon to ["Xenopus" romeri + xenopodines], and Saltenia is the sister to [Eoxenopoides + pipines]. Whereas the addition of fossil taxa did not affect previous hypotheses of the relationships among extant taxa of pipoid anurans, it did alter and supplement interpretations of character evolution. Moreover, owing to the inclusion of fossil taxa, several characters that previously had not been included in neontological studies were examined.