Ana María Báez

A new helmeted frog (Anura: Calyptocephalellidae) from an Eocene subtropical lake in northwestern Patagonia, Argentina

ABSTRACT Eocene caldera-lake deposits from Río Pichileufú have yielded anuran remains in association with a taxonomically diverse flora. The floral evidence suggests that these anurans lived under climatic conditions similar to those of extant subtropical rainforests. One of the anurans is a helmeted neobatrachian, which is represented by articulated remains and represents a new species that can be assigned to the extant genus Calyptocephalella on the basis of both cranial and postcranial traits. Calyptocephalella pichileufensis, gen. et sp. nov., indicates that, despite the relatively conservative skeletal anatomy of the genus, Calyptocephalella has not always been associated with the temperate austral forests that it inhabits today. The new species also provides evidence of a biotic link with Australia, which has been proposed on the basis of other faunal and floral records, as well as on the paleogeographic history of Patagonia during the mid-Cretaceous—Eocene interval. We also discuss the significance of neobatrachian cranial features that might reflect hyperossification.

The Archaic Ilial Morphology of an Enigmatic Pipid Frog from the Upper Pleistocene of the South American Pampas

ABSTRACT 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 three 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 have been collected from Pleistocene beds in Argentina, nearly 2000 km farther south than their present distribution on the continent. Here, we describe a well-preserved pipid ilium possessing features unknown in the living taxa. The fossil is from a new Lujanian (late Pleistocene) locality of the Pampean Region, thereby confirming the intriguing presence of this group in southern South America. We provide a detailed anatomical evaluation of the adult iliac morphology of pipimorphs and use these data, along with molecular data, in a parsimony analysis of living and extinct pipoid taxa to estimate the relationships of the new material. This analysis places the fossil as a stem xenopodine in an unresolved polytomy together with “Xenopus” romeri from the upper Paleocene—lower Eocene of Brazil and two taxa from the Eocene of Patagonia. These Pleistocene pipid records in the Pampean region and subsequent disappearance may reflect latitudinal shifts owing to the rapid climate changes related to the glacial/interglacial cycles.

A NEW SPECIES OF NOTOBATRACHUS (AMPHIBIA, SALIENTIA) FROM THE MIDDLE JURASSIC OF NORTHWESTERN PATAGONIA

Abstract Notobatrachus degiustoi is the most completely known Jurassic frog and has been recorded in many outcrops of the La Matilde Formation of the Deseado Massif area in southern Patagonia. Herein, we erect a new species of the genus based on partially articulated remains collected from the Callovian Las Chacritas Member of the Cañadón Asfalto Formation, about 500 km northwest of the northern limit of the known geographical distribution of N. degiustoi. The new species differs from the latter in having a maxilla with a distinct pterygoid process and lacking teeth at least along the posterior two-thirds of its length, and a complete maxillary arch. We also provide an expanded diagnosis of Notobatrachus. This finding adds to our understanding of the early diversification of frogs.

Intraspecific morphological variation and its implications in the taxonomic status of ‘Bufo pisanoi,’ a Pliocene anuran from eastern Argentina

ABSTRACT The true toad family Bufonidae is one of the most speciose and widespread clades of neobatrachian anurans. Despite being well represented in South America at present, bufonids have a poor fossil record on this continent. ‘Bufo pisanoi’ from Pliocene outcrops of coastal Buenos Aires Province, Argentina, is the only extinct South American bufonid taxon recognized to date. In this study, we investigated the validity of the putative diagnostic characters of this extinct species to confirm its taxonomic status based on revision of the holotype and referred material. Comparisons with several extant bufonid species led us to include the taxon represented by this fossil material within the Rhinella marina clade, close to R. arenarum. Further comparisons and a geometric morphometric analysis based on a relatively large sample of the latter species demonstrated that the morphology of ‘B. pisanoi’ falls within the variation range of R. arenarum. Therefore, we consider that the names ‘B. pisanoi’ and R. arenarum represent the same taxon, with the latter having priority. This work emphasizes the importance of considering intraspecific variation whenever possible, because this leads to a more rigorous approach to the identification of fossil specimens and tests the taxonomic value of different osteological characters.

Dealing with homoplasy: osteology and phylogenetic relationships of the bizarre neobatrachian frog Baurubatrachus pricei from the Upper Cretaceous of Brazil

The hyperossified frog Baurubatrachus pricei Báez & Peri 1989 from the Maastrichtian Serra da Galga Member of the Marília Formation is described in detail, as preparation of the type and only known specimen revealed significant features, particularly of the pectoral and pelvic girdles. This species is rediagnosed on the basis of the combination of plesiomorphic and derived character states, including two unique traits: cranial roof with round openings that might have contained the tympanic membrane completely circumscribed by ornamented dermal bone, and scapula bearing a conspicuous crest deflected ventrally to form a deep basin on its leading edge. Since its discovery it was suggested that Baurubatrachus might be a relative of the South American ceratophryids, a phylogenetic placement endorsed by recent analyses. In order to test this hypothesis considering all the available information, we conducted several maximum parsimony analyses under different weighting schemes and topological constraints, scoring 143 characters for 71 extant and extinct anuran taxa. Our taxonomic sampling included species with well-ossified dermatocrania as well as less ossified members of main neobatrachian clades to explore the impact of hyperossification, which frequently drives groupings based on homoplastic features. We also assessed the phylogenetic signal provided by cranial and postcranial partitions. Although we recovered a monophyletic Ceratophryidae repeatedly, Baurubatrachus was not related with this nobleobatrachian group but associated with the calyptocephalellid australobatrachians, although with weak support. Other possible phylogenetic placements are also discussed, as well as microhabitat and habits, taking into account both anatomical and geological data.