Raúl O. Gómez

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.

The youngest South American rhynchocephalian, a survivor of the K/Pg extinction

Rhynchocephalian lepidosaurs, though once widespread worldwide, are represented today only by the tuatara (Sphenodon) of New Zealand. After their apparent early Cretaceous extinction in Laurasia, they survived in southern continents. In South America, they are represented by different lineages of Late Cretaceous eupropalinal forms until their disappearance by the Cretaceous/Palaeogene (K/Pg) boundary. We describe here the only unambiguous Palaeogene rhynchocephalian from South America; this new taxon is a younger species of the otherwise Late Cretaceous genus Kawasphenodon. Phylogenetic analysis confirms the allocation of the genus to the clade Opisthodontia. The new form from the Palaeogene of Central Patagonia is much smaller than Kawasphenodon expectatus from the Late Cretaceous of Northern Patagonia. The new species shows that at least one group of rhynchocephalians not related to the extant Sphenodon survived in South America beyond the K/Pg extinction event. Furthermore, it adds to other trans-K/Pg ectotherm tetrapod taxa, suggesting that the end-Cretaceous extinction affected Patagonia more benignly than the Laurasian landmasses.

An overview of the ilium of anurans (Lissamphibia, Salientia), with a critical appraisal of the terminology and primary homology of main ilial features

ABSTRACT The ilium has been considered a ‘key’ element in anuran paleontology, but its terminology is inconsistent across the literature. Therefore, we here review the terminology used so far to describe anuran ilia and provide an annotated glossary of main ilial features. We also survey ilial morphology and comment on variation exhibited by each ilial feature among major anuran lineages. We do so with special consideration for myological correlates, provide muscle maps for a few species, and aim to clarify hypotheses of primary homology. We consider previous work that compartmentalizes part of the described variation into cladistic characters, with the intention of providing a starting point for using ilial features in future research on osteology-based phylogenetics of anurans. Finally, we remark on some aspects regarding the dorsal prominenceprotuberance complex.

Oldest record of Leptodactylus Fitzinger, 1826 (Anura, Leptodactylidae), from the early Pliocene of the South American Pampas

ABSTRACT The Neotropical frog genus Leptodactylus is one of the most taxonomically diverse of all neobatrachian anurans. Despite the genus being highly diversified and widely distributed today, the fossil record is scanty and restricted to the Quaternary of the Neotropics. Here, we report and describe a new record of total group Leptodactylus from the Chapadmalalan (early Pliocene) of the South American Pampas. We evaluate both qualitative and quantitative characters and discuss the taxonomic value of body size in the context of living Leptodactylus. A number of features of the fossil elements suggests an affinity with the living species of the L. latrans species group and, particularly, with L. latrans. However, the lack of resolution of Leptodactylus interrelationships and, thus, the lack of osteological synapomorphies of the species groups and species within the genus conspire to force allocation of the fossils to crown Leptodactylus until they are studied in a rigorous phylogenetic context. In any case, the new material constitutes the oldest record of total group Leptodactylus and extends their stratigraphic range back to the early Pliocene.

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.

First fossil record of the South American frog genus Odontophrynus Reinhardt and Lütken, 1862 (Anura, Neobatrachia)

ABSTRACT The frog genus Odontophrynus comprises 10 species arranged in three species groups that inhabit southeastern South America. In Argentina, it is represented by the O. americanus and O. occidentalis species groups and, despite being a fairly common taxon of the extant herpetofauna, it has no known fossil record. Here we report on the first fossil record of the genus, based on an almost complete right ilium from the lower levels of the Buenos Aires Formation (OIS 11, Bonaerian age, middle Pleistocene) in the Bonaerian Pampas of Argentina. The taxonomic allocation is derived from a thorough survey of anuran ilia and is grounded in a set of distinct ilial characters that, in combination, do not occur in any other anuran. These include: ilium not fused to ischium; well-developed dorsal acetabular expansion; broad preacetabular zone with a shallow preacetabular fossa; straight ilial shaft lacking dorsal ridge; and spike-like dorsal prominence bearing a distinct dorsal protuberance. Additionally, after comparing with a large sample of specimens representing most species of Odontophrynus, we propose two main characters (high spike-like dorsal prominence, absence of a lateral knob on the dorsal prominence) that allow referral to Odontophrynus aff. O. americanus or O. cordobae.

A new species of the Pleistocene furnariid Pseudoseisuropsis (Aves, Passeriformes)

ABSTRACT Pseudoseisuropsis wintu sp. nov. is described from cranial material that had formerly been designated as a paratype of the extinct Pseudoseisuropsis nehuen. Thorough comparisons were made between the cranial specimens ascribed to Pseudoseisuropsis and many extant furnariid species. This new species is lower Pleistocene in age and increases the known diversity of Pseudoseisuropsis to three species. Cladistic analyses were performed using 43 cranial characters and a backbone constraint based on a well-supported phylogeny from a recent molecular analysis. In the most parsimonious tree, Pseudoseisuropsis was retrieved as a sister group of woodcreepers (Dendrocolaptinae) with low support. However, slightly suboptimal hypotheses, which could not be completely ruled out, suggest that this genus may be more closely related to other clades of Furnariidae. Hence, we agree with previous authors in regarding Pseudoseisuropsis as Furnariidae Incertae sedis. In addition, two fragmentary fossils ascribed to Pseudoseisuropsis were included in taxonomic comparisons: P. cuelloi, in order to assess the possibility that P. wintu sp. nov. belongs to that species, and another paratype of P. nehuen, to reassess its taxonomic identity.