Claudia I. Montalvo

New Tupinambis Remains from the Late Miocene of Argentina and a Review of the South American Miocene Teiids

Abstract The most abundant and diverse records of teiids in the South American Miocene are from early and middle Miocene of Patagonia (Argentina) and Colombia. Only two genera of tupinambines are recognized: Paradracaena and Tupinambis. In this contribution, we describe remains assigned to Tupinambis from the late Miocene Cerro Azul Formation. The fossils were collected in exposures of this unit at several localities in the province of La Pampa, central Argentina. Evolutionary history and biogeography of South American tupinambines were affected by the environmental-climatic change subsequent to the uplift of the Andes. Among the taxa represented in the Miocene, Paradracaena became extinct, whereas Tupinambis survived restricted to environments with a more benign climate, disappearing from Patagonia but not from central Argentina.

Snakes from the Cerro Azul Formation (Upper Miocene), Central Argentina, with a review of fossil viperids from South America

Abstract South America contains a diverse Miocene snake record. Heretofore, the most significant assemblages were from the early and middle Miocene of Patagonia and Colombia. Colubroid vertebrae assignable to the ‘Colubridae’ and Viperidae are here reported from the upper Miocene Cerro Azul Formation at Caleufú, in La Pampa province, central Argentina. The viperid fossil is the oldest record of the family in South America and, together with molecular evidence, it supports the hypothesis of viperids first entering South America prior to the closure of the Isthmus of Panamá. South American viperid specimens also have been recognized from the Pliocene (aff. Bothrops) and Pleistocene of Buenos Aires province, Argentina. The presence of Bothrops during the early–middle Pleistocene near La Plata city suggests that during more humid intervals this genus had a wider distribution than at present. A previous report of a viperid from the late Pleistocene of Bolivia cannot be corroborated.

Phylogenetic affinities of the late Miocene echimyid †Pampamys and the age of Thrichomys (Rodentia, Hystricognathi)

Abstract Phylogenetic affinities of the late Miocene echimyid †Pampamys emmonsae Verzi, Vucetich, and Montalvo, 1995 (Huayquerian South American Land Mammal Age, central Argentina), were analyzed. In the most-parsimonious tree obtained, subfamilies of Echimyidae were nonmonophyletic (except for Dactylomyinae). Two major clades were recovered. One of them included the living fossorial Eumysopinae and the extinct †Theridomysops. The other clade grouped the terrestrial eumysopines Thrichomys (punaré) and Proechimys–Trinomys (spiny rats), and the arboreal eumysopines Mesomys (spiny tree-rats) + Echimyinae–Dactylomyinae. †Pampamys was the sister genus of Thrichomys, suggesting the Huayquerian South American Land Mammal Age (>6.0 million years ago [mya] by biochronology) as a minimum age for the origin of the living genus. Both major echimyid clades recognized here are represented by simplified-molared species in the Huayquerian South American Land Mammal Age. This would be related to the expansion of open environments during the late Miocene, and the geographical bias of the fossiliferous Huayquerian deposits exposed mostly in southern South America.

Late Miocene continental birds from the Cerro Azul Formation in the Pampean region (central-southern Argentina)

Cenizo, M.M., Tambussi, C.P. & Montalvo, C.I., iFirst Article. Late Miocene continental birds from the Cerro Azul Formation in the Pampean region (central-southern Argentina). Alcheringa, 1–22. ISSN 0311-5518. The oldest known birds from the Cerro Azul Formation are described, including the oldest records for the genera Eudromia and Nothura (Tinamidae), Milvago (Falconidae), Pterocnemia (Rheidae) and an undetermined Tyrannidae. The first remains of Phorusrhacidae for this formation are reported and a specimen previously referred to the giant teratorn Argentavis magnificens is reassigned to this family. We outline and update the current knowledge of the groups studied herein. The palaeornithological record from the Cerro Azul Formation is congruent with palaeoenvironmental inferences previously drawn from mammalian assemblages recovered from this unit, which point to the existence of open environments, possibly xerophyllous shrubby steppes, perhaps with some trees. These records are the first indications of a typically Pampean bird fauna at the end of the late Miocene in central-southern Argentina.

Estudio tafonómico de los mamíferos pleistocenos del yacimiento de Playa del Barco (Pehuen Co), provincia de Buenos Aires, Argentina

Abstract. Taphonomic study of Pleistocene mammals from Playa del Barco site (Pehuen Co) Buenos Aires Province, Argentina. Results are presented of a comparative taphonomic study conducted on mammal remains from Playa del Barco, Buenos Aires Province, Argentina. Two bearing levels, belonging to a fluvial environment were recognized: one constituted mainly by conglomerates and the other by silty sandstones. The mammal remains collected belong to the orders Xenarthra, Notoungulata, Litopterna, Rodentia, Carnivora, Perissodactyla, Artiodactyla, and Proboscidea, all of them components of the typical Pleistocene megafauna. When taking into account the source level, variations in the taphonomic attributes of the analysed materials were observed. Remains from the conglomerate show evidence of having been rapidly buried and then reelaborated before their final deposition. Fossils from silty sandstones show signs of longer exposure to weather, more intensely subject to processes that took place before burial. Due to their characteristics they are interpreted as re-deposited remains. In both cases, processes related to mass transport are inferred. Nevertheless, the diversity in conservation status and taphonomic attributes would result from processes originated at each of the source levels. The lithostratigraphic, taxonomic, and taphonomic evidences do not allow relating these two levels to a unique event. Therefore, the fossils that they contain are interpreted as members of two different associations.

New Records of Squamates from the Upper Miocene of South America

Abstract The Cerro Azul Formation of Argentina has yielded one of the highest diversities of squamate reptiles for the upper Miocene of South America including tupinambine teiids (Tupinambis sp.), “colubrids,” and viperids. Here, we describe new remains of Tupinambis sp. and “Colubridae” from this Formation as well as the first records of teiine teiids and boid snakes. The teiine represents the oldest record of this subfamily in South America. The squamate assemblage of the Cerro Azul Formation is consistent with the mammalian fauna in supporting the interpretation of a Chacoan-type palaeoenvironment for the upper Miocene of Central Argentina.

A NEW SPECIES OF REIGECHIMYS (RODENTIA, ECHIMYIDAE) FROM THE LATE MIOCENE OF CENTRAL ARGENTINA AND THE EVOLUTIONARY PATTERN OF THE LINEAGE

Abstract . The genus Reigechimys (Rodentia, Echimyidae) was originally described on the basis of two mandibular fragments recovered from Huayquerian (late Miocene) outcrops of the Cerro Azul Formation in La Pampa Province (Argentina). The included species (R. plesiodon Verzi et al. and R. octodontiformis Verzi et al.) represent a peculiar lineage characterized by its molar morphology with occlusal simplification that is extreme for the family. New materials recently found at the Cerro Azul Formation allow for a more detailed knowledge of the variation of Reigechimys and recognition of a new species, Reigechimys simplex sp. nov. characterized by the absence of mesoflexid/fossettid in the m1–2. The morphological changes of Reigechimys are described in the context of the turnover exhibited by octodontoid rodents in the Huayquerian of the Cerro Azul Formation. The polarity of changes described for Reigechimys is consistent with those of the other lineages. This evolutionary pattern enhances the biochronological interpretation of the Huayquerian in this formation.

Late Miocene capybaras from Argentina: Skull anatomy, taxonomy, evolution, and biochronology

Fossil capybaras are morphologically extremely varied, but previous studies have disagreed on whether this diversity reflects intraspecific variation or the existence of multiple species. Here, we review the capybaras from the classic Argentinian Late Miocene localities of Paraná River cliffs (“conglomerado osífero” of the Ituzaingó Formation, Entre Ríos), and Chillhué and Guatraché shallow lakes (Cerro Azul Formation, La Pampa), and perform a morphometric analysis of their upper cheek teeth and the posterior portion of the rostrum. Our results confirm that all of the specimens from the “conglomerado osífero” belong to the single species Cardiatherium paranense. In addition, we refer a specimen from Tupungato (Río de los Pozos Formation, Mendoza) to C. paranense, thus expanding its geographical range. The material from La Pampa represents a different taxon, and is here preliminary referred to Cardiatherium aff. orientalis. Our systematic interpretation of Late Miocene capybaras suggests that the early radiation of this group was not as explosive as previously thought, and was likely constrained by the early acquisition of large size, increasing complexity of the cheek teeth, and probably semi-aquatic habits.

The Taxonomic Status of the Pliocene Capybaras (Rodentia) Phugatherium Ameghino and Chapalmatherium Ameghino

Abstract. Living capybaras are a unique group of rodents. They have ever-growing cheek teeth with a complicated occlusal morphology that changes even after birth. Concerning fossil capybaras this morphological change, associated with increasing size, led to regard them as taxonomically highly diverse, including small species with simple dental morphology, and large species with complicated cheek teeth, considered as primitive and derived, respectively. Recently, it was proposed that the different morphs found in each locality actually represent individuals of different ontogenetic stages of a population or successive populations, rather than a multiplicity of coeval species in different stages of evolution. For the Pliocene, the richest locality for capybaras is Farola Monte Hermoso on the southern coast of Buenos Aires Province. This locality yielded four nominal species of capybaras, three of them are a small morph (Phugatherium cataclisticum Ameghino, “Anchimysops villalobosi” Kraglievich, “A. ultra” Kraglievich) and the other a large one (“Chapalmatherium perturbidum” (Ameghino)). In this paper we propose that they represent juveniles and adults of one species, P. cataclisticum. In order to evaluate the phylogenetic position of Phugatherium within Cavioidea a cladistic analysis was performed modifying a previously published combined matrix of morphology and DNA sequences. Phugatherium forms a monophyletic group and is the sister group of modern capybaras. Within Phugatherium the most basal species is P. novum Ameghino, whereas the type species P. cataclisticum is the sister group of P. saavedrai Hoffstetter, Villarroel and Rodrigo.

MINERALOGY, GEOCHEMISTRY AND PALEOHISTOLOGY OF PLIOCENE MAMMALS FROM THE MONTE HERMOSO FORMATION (ARGENTINA). PAEDOTHERIUM BONAERENSE (NOTOUNGULATA, HEGETOTHERIIDAE) AS A CASE STUDY

Abstract . We describe and analyze the mineralogical, geochemical and paleohistological characteristics present in hemimandibles of Paedotherium bonaerense (Ameghino) (Mammalia, Notoungulata, Hegetotheriidae). Remains were recovered from floodplain deposits of the Monte Hermoso Formation (early Pliocene). Francolite is the main mineral component in all hemimandibles, evidencing compositional changes in the internal crystalline structure during fossil-diagenesis. The similarity in the chemical composition of the fossils and the hosting rocks suggests that the enrichment of the remains with new elements was due to direct exchange with the sediments in which they were buried. Original bone microstructure shows good preservation, only affected by permineralization and microfissures. Manganese and iron oxides are the most abundant minerals infilling microstructural features and microfissures. The dark color identified on the outer surface of some remains is related to precipitation of manganese oxides. The results obtained allow us to establish the processes affecting the remains before and after burial, and thus interpret the different taphonomic histories. This work provides new information on a issue usually not considered in studies on vertebrate communities from the South American Neogene and at the same time it establishes a framework for the analysis of assemblages with similar characteristics.