On the development of the chondrocranium and the histological anatomy of the head in perinatal stages of marsupial mammals

An overview of the literature on the chondrocranium of marsupial mammals reveals a relative conservatism in shape and structures. We document the histological cranial anatomy of individuals representing Monodelphis domestica, Dromiciops gliroides, Perameles sp. and Macropus eugenii. The marsupial chondrocranium is generally characterized by the great breadth of the lamina basalis, absence of pila metoptica and large otic capsules. Its most anterior portion (cupula nasi anterior) is robust, and anterior to it there are well-developed tactile sensory structures, functionally important in the neonate. Investigations of ossification centers at and around the nasal septum are needed to trace the presence of certain bones (e.g., mesethmoid, parasphenoid) across marsupial taxa. In many adult marsupials, the tympanic floor is formed by at least three bones: alisphenoid (alisphenoid tympanic process), ectotympanic and petrosal (rostral and caudal tympanic processes); the squamosal also contributes in some diprotodontians. The presence of an entotympanic in marsupials has not been convincingly demonstrated. The tubal element surrounding the auditory tube in most marsupials is fibrous connective tissue rather than cartilage; the latter is the case in most placentals recorded to date. However, we detected fibrocartilage in a late juvenile of Dromiciops, and a similar tissue has been reported for Tarsipes. Contradictory reports on the presence of the tegmen tympani can be found in the literature. We describe a small tegmen tympani in Macropus. Several heterochronic shifts in the timing of development of the chondocranium and associated structures (e.g., nerves, muscles) and in the ossification sequence have been interpreted as largely being influenced by functional requirements related to the altriciality of the newborn marsupial during early postnatal life. Comparative studies of chondocranial development of mammals can benefit from a solid phylogenetic framework, research on non-classical model organisms, and integration with imaging and sectional data derived from computer-tomography.Fil: Sánchez Villagra, Marcelo R.. Universitat Zurich; SuizaFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Academic Language Teaching and Learning in the Third Space Classroom: A Preservice Teachers\u27 Perspective

The increased percentage of immigrant children in the public school system in the United States has challenged schools to provide adequate academic language instruction to reach the same levels as their monolingual peers. Teachers must demonstrate the ability to support the development of academic language in accordance to both the standards\u27 requirements and the linguistic needs of culturally and linguistically diverse students. It is very important to shed light on teacher preparation programs and how they support their candidates to develop a pedagogy that can best respond to students\u27 needs. This study explore the beliefs and practices of preservice teachers as they plan and implement curriculum for academic language development. This study took place at an elementary school in the San Francisco Bay. The participants were five student-teachers in their final semester of practicum at this school and in the Multiple Subject credential program at a university in the same area. The supervisor and researcher collected the results of the academic language survey, questionnaires and lesson plans. She transcribed observations of the participants\u27 teaching practices, debriefing sessions and the conversations with the participants. Four themes emerged from the data: interaction as a tool to deepen learning, bridging students\u27 home and school experiences, teacher facilitation, multimodality: using multiple modes to make meaning; additional factors influencing teaching. The participants demonstrated an ability to navigate the third space classroom by implementing their beliefs about teaching and learning academic language and by adapting to their students\u27 learning needs, and planning according to the expectations of the institution. This study ended with several recommendations for credentialing programs to best support their candidates in teaching academic language in the diverse classroom. The study brought to light the importance of a strong field experience in a third space bilingual, bicultural, and economically disadvantaged school context. Such a context has revealed to be a strong prediction of preservice teachers\u27 success in negotiating their identity of academic language teachers

Santiago Roth and his scientific legacy: a reappraisal of the Swiss collections

The Pampean Region in the eastern central part of Argentina is today an agricultural zone, the main national food producer, and the base for a population that holds in big cities more than half of the 46 million inhabitants of the country. A century ago, Pampean landscapes were dominated by native grasslands, gallery forests confined to riverbanks, sparse dry forests towards the west of the area, and on the horizon of the flat Pampas, occasional isolated ombú trees (Phytolacca dioica) and eucalyptuses planted by the increasing population to provide shade in hot days and protection during storms for domesticated animals and people. Native birds, reptiles, and mammals, now replaced by humans and human activities, were certainly more frequent than today. However, these same riverbanks and lowlands were places where fossil hunters such as Santiago Roth could find bizarre extinct creatures that lived hundreds of thousands of years ago. The main attractions were the bones and teeth of megamammals, such as huge ground sloths (Megatherium americanum) which weighed more than four tonnes; big armadillos, such as Panochthus tuberculatus, with the size of a small car; strange ungulates having nasal apertures on the top of the skull that likely sported a trunk, as in the case of Macrauchenia patachonica; predators with hyper-enlarged sabertooth canines like the felid Smilodon populator, all contemporaneous with local gigantic spectacled bear relatives; proboscideans; native horses; deer with elaborate antlers; and other creatures living in South America in the near past of the Pleistocene. The Pampean Region was and still is a region where the remaining of these lost species can be found. Radiocarbon dating has demonstrated that several of these megammamals coexisted with the first humans in the area around 12,000– 11,000 years ago. Did they interact? Did humans hunt them, and perhaps cause their extinction? Santiago Roth contributed to all of these topics by making new discoveries and publishing on them. Santiago Roth was a Swiss naturalist, explorer, and palaeontologist who spent most of his active life in Argentina, where he died at the age of 74 years. At the end of the nineteenth century, Santiago Roth (then 16 years) and his family moved from Switzerland to Argentina in search of better opportunities. In Argentina, he grew up in a young republic beset by war and social revolts, but ultimately accomplished a great deal in support of the scientific development of the country. In his young years, he started collecting objects of natural sciences, including fossils. Some of his palaeontological collections from the Pampean Region were sold in Europe. Six of them were associated with catalogues, in which a number identifies the specimen, taxonomic determination, material found, and provenance. Some of these collections are still kept intact in Copenhagen and Zurich. Other fossil specimens collected by Roth are today in natural history museums in Geneva and Lausanne. Santiago Roth was a multifaceted person. His contributions to science went well beyond palaeontology and embraced other disciplines, such as geology, geomorphology, and stratigraphy. Together with the founder Keywords Megafauna, Fossil, Vertebrate palaeontology, Exploration, Pampas, Argentina, Switzerlan

Cladosictis patagonica (Metatheria, Sparassodonta) from the Collón Cura Formation (Middle Miocene), Río Negro, Argentina

We studied new specimens of Cladosictis patagonica (Metatheria, Sparassodonta) from the Middle Miocene Collón Cura Formation (Río Negro, Argentina). We reported here this taxon for first time for this stratigraphic unit, analyzed the report considering the intraspecific variability, and discussed the finding in the context of other sparassodonts already known for the Collón Cura Formation.Fil: Echarri, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Ulloa Guaiquin, Karen Silvana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Aguirrezabala, Guillermo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

First record of Glyptodon Owen (Mammalia, Xenarthra, Cingulata) in the Pleistocene of Mendoza Province (Argentina)

Poco se conoce aún sobre la fauna del Pleistoceno de la provincia de Mendoza en relación a otras regiones de la Argentina. Los géneros previamente reconocidos son: Megatherium, Mylodon, Glossotherium, Macrauchenia, Paleolama, Hippidion y Equus. En esta nota comunicamos los primeros restos de Glyptodon sp. (Xenarthra, Cingulata, Glyptodontidae), los que fueron hallados en la margen oeste del río Tunuyán, Departamento de Tupungato, en sedimentitas de la Formación El Zampal. Este espécimen de Glyptodon representa el registro más occidental para la Argentina.Comparing with other regions of Argentina, few Pleistocene mammalian records are known from Mendoza Province. The genera previously recognized are: Megatherium, Mylodon, Glossotherium, Macrauchenia, Paleolama, Hippidion, and Equus. In this note, the first occurrence of Glyptodon sp. (Xenarthra, Cingulata, Glyptodontidae) is reported. The material was found in outcrops of the El Zampal Formation located on the west margin of the Tunuyán River, Tupungato Department. This finding represents the westernmost record of Glyptodon in Argentina.Fil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentina. Museo Municipal de Historia Natural San Rafael - Unidad Asociada al CCT Mendoza; ArgentinaFil: Martinelli, Agustín Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Municipal de Historia Natural San Rafael - Unidad Asociada al CCT Mendoza; ArgentinaFil: Zurita, Alfredo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Ponce, Hernan. Dirección de Recursos Naturales Renovables, Delegación Valle de Uco, Mendoza; Argentin

Paleontology and stratigraphy of the Aisol Formation (Neogene), San Rafael, Mendoza

Fil: Forasiepi, Analía Marta. Departamento de Paleontología. Museo de Historia Natural de San Rafael; ArgentinaFil: Martinelli, Agustín Guillermo. Departamento de Paleontología. Museo de Historia Natural de San Rafael; ArgentinaFil: De la Fuente, Marcelo Saúl. División Paleontología Vertebrados; Facultad de Ciencias Naturales y Museo; Universidad Nacional de La Plata; ArgentinaFil: Dieguez, Sergio. Departamento de Paleontología. Museo de Historia Natural de San Rafael; ArgentinaFil: Bond, Mariano. División Paleontología Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plat

3D digital endocast of the early miocene (Colhuehuapian) sipalocyon externa (Metatheria, Sparassodonta)

The skull of Sipalocyon externa Ameghino, 1902 (Hathliacynidae) from Sacanana, Chubut, Sarmiento Formation, Colhuehuapian age, is studied (MACN-CH1911).We first record the taxon for this locality, which includes the sparassodonts Acrocyon riggsi Simpson 1930 and a large Borhyaenoidae. The skull is almost complete andwas studied through μCT-scanning, representingthe first digital encephalic cavity cast(c) for Sparassodonta and one of the few known for stem marsupials. Body massof the specimen was estimated based on teeth measurements, following Gordon´s equations (1.7 kg), and skull centroid-size, inspired by Zelditch (2.8 kg). Considering the mean body mass, its encephalization quotient with and without olfactory bulbsc is respectively: 0.32 and 0.30 (Jerison equations) or 0.41 and 0.38 (Eisenberg equations). The estimates for S. externastand between that recorded by Macrini for the marsupials Didelphis virginiana (Kerr, 1792) and Dasyurus hallucatus Gould, 1842 but are larger than those for the stem marsupial Pucadelphys andinus Marshall and De Muizon, 1988.The olfactory bulbc represents 5.88% of the total endocranial volume, which is smaller than the values for P. andinus (11.7 %) and other marsupials (8 %?11 %).The paraflocculusc corresponds to 2.65 %, representing a large proportionof the endocast. This agrees with a deep subarquate fossa (a primitive condition for Metatheria).Vascular organization is largely conservative in this species. Similar to other sparassodonts, the major venous drainage from the endocranium was through the cerebrospinal system instead of jugular vein.In addition, we detected for the first time in this group an accessory transverse sinus enclosed by cranial bone.Fil: Gaillard, Charlene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Tarquini, Sergio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; ArgentinaFil: Hernández del Pino, Santiago Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Ladeveze, S.. Universite de Paris. Museum National D´historie Naturelle; FranciaFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaReunión de Comunicaciones de la Asociación Paleontológica ArgentinaLa PlataArgentinaAsociación Paleontológica ArgentinaUniversidad Nacional de La Plata. Facultad de Ciencias Naturales y MuseoFundación Museo de La Plata “Francisco Pascasio Moreno

Stratigraphy, fossil mammals, and age of the Eocene-Miocene volcano-sedimentary sequences of sierra Huantraico-sierra Negra and cerro Villegas (Neuquén Province, Argentina)

Se presentan los recientes avances en el conocimiento de la estratigrafía y la edad de las unidades volcanosedimentarias cenozoicas expuestas en el área de sierra de Huantraico-sierra Negra y cerro Villegas (Departamento Pehuenches, provincia del Neuquén, Argentina). Los análisis estratigráficos y de los restos fósiles hallados permiten reconocer y diferenciar seis unidades litoestratigráficas: a. ʻRodados Lustrosos’ (Eoceno Tardío-Oligoceno Temprano?), conformados por conglomerados gruesos texturalmente maduros (hasta 18 m de espesor) dispuestos sobre un marcado paleorrelieve labrado en sedimentitas preeocenas (fase diastrófica Incaica); b. Formación Rincón Escondido (nom. nov.) (Oligoceno Temprano-Oligoceno Tardío bajo), compuesta por depósitos fluviales de dominio psamítico asociado a un fuerte aporte piroclástico (31 m), se dispone y rellena el mismo paleorrelieve sobre el cual se sitúan los ʻRodados Lustrosos’; c. Formación Sierra Negra (nom. nov.) (Aquitaniano-Burdigaliano, Mioceno Temprano), suprayace a un nuevo paleorrelieve que llega a erosionar hasta depósitos del Cretácico Temprano (fase diastrófica Pehuenche); esta unidad puede subdividirse en el Miembro Filo Morado (hasta 250 m de basaltos alcalinos olivínicos, pirocalstitas, depósitos volcanoclásticos y sedimentarios volcanogénicos) y el Miembro Puesto Tillerías (nom. nov.) (hasta 600 m de coladas basálticas y andesíticas con intercalaciones de tobas y tufitas); d. Formación Pichi Tril (Burdigaliano tardío-Langhiano), conformada por cuerpos intrusivos de composición andesítica, cuyo emplazamiento se vincula a una deformación acaecida a fines del Mioceno Temprano (fase diastrófica Quechua); e. Formación Desfiladero Negro (Tortoniano Temprano), que conforma un conjunto de diques básicos que atraviesan al resto de la sucesión-una intrusión relacionada con deformación del Mioceno Tardío bajo; f. Formación La Tiza (Tortoniano tardío?-Mesiniano temprano, Mioceno Tardío), compuesta por hasta 85 m de depósitos conglomerádicos oligomícticos gruesos de baja madurez textural, originados a partir de la erosión de los cuerpos volcánicos y las coladas de la Formación Sierra Negra. La sucesión completa fue nuevamente deformada hacia finales del Mioceno (Mesiniano tardío). El hallazgo de restos de mamíferos fósiles en las formaciones Rincón Escondido (nom. nov.) y Sierra Negra (nom. nov.), sumadas a las dataciones radiométricas efectuadas por otros autores, han permitido calibrar geocronológicamente a las unidades volcanosedimentarias de esta región.We present here the recent advances in understanding the stratigraphy and age of the Cenozoic volcanic and sedimentary sequences exposed on the area of sierra Huantraico-sierra Negra and cerro Villegas (Pehuenches Department, Neuquén Province). Stratigraphic analyses and recovered fossil remains allow us to recognize and differentiate six litostratigraphic units: a. The 'Rodados Lustrosos' (Late Eocene-Early? Oligocene), composed of coarse-grained texturally mature conglomerates (up to 18 m thick), deposited on a strong paleorelief of eroded pre-Eocene sedimentary rocks (Inca diastrophic phase); b. The Rincón Escondido Formation (nom. nov.) (early Oligocene-lower Late Oligocene), composed of sandy fluvial deposits linked to a strong pyroclastic source (31 m), occupies and fills the same paleorelief on which the 'Rodados Lustrosos' lies; c. The Sierra Negra Formation (nom. nov.) (Aquitanian-Burdigalian, Early Miocene) overlies a younger paleorelief that erodes into deposits as old as Early Cretaceous (Pehuenche diastrophic phase); this unit can be subdivided into the Filo Morado Member (up to 250 m of olivine-alkaline basalts, pyroclastic rocks, and volcanogenic deposits) and the Puesto Tillerías Member (nom. nov.) (up to 600 m of basalts and andesitic rocks with interbedded tuffs and tuffites); d. The Pichi Tril Formation (late Burdigalian-Langhian) is composed of andesitic intrusive bodies linked to deformation that occurred by the end of the Early Miocene (Quechua diastrophic phase); e. The Desfiladero Negro Formation (early Tortonian) forms a set of basic dikes that cross the rest of the succession - an intrusion related to earliest Late Miocene deformation; f. The La Tiza Formation (late? Tortonian-early Messinian, Late Miocene), composed of up to 85 m of coarse-grained oligomictic conglomerates with low textural maturity, originated from the erosion of volcanic bodies and basaltic flows of the Sierra Negra Formation. This entire succession was again deformed at the end of the Miocene (late Messinian). The discovery of fossil mammals in the Rincón Escondido and Sierra Negra formations, together with radiometric dates provided by previous authors, have allowed a geochronologic calibration of the volcano-sedimentary units exposed in this region.Facultad de Ciencias Naturales y Muse

On the Art and Natural History of Paul Magne de la Croix (1875-1942) and Carlos Rusconi (1898-1969)

En esta contribución presentamos el perfil artístico del renombrado paleontólogo argentino Carlos Rusconi, quien ha realizado numerosas reconstrucciones de animales extintos así como dibujos científicos a lo largo de su carrera. En particular, su publicación “La Vida Animal en el Terciario Superior de Buenos Aires” (1933) y su libro “Animales Extinguidos de Mendoza y de la Argentina” (1967), con dibujos de Paul Magne de la Croix, representan íconos de la divulgación paleontológica argentina. Por otro lado, presentamos datos biográficos hasta ahora desconocidos sobre el artista Francés Paul Magne de la Croix, así como sus aportes a la historia natural. Magne de la Croix fue un personaje multifacético, casi olvidado, que poco se conoce sobre su vida personal, mientras que sus obras están diseminadas en numerosas contribuciones de distintas índoles. Los trabajos de ambos personajes fueron la base para la divulgación de la paleontología sudamericana y su arte ha aparecido repetidamente en libros, publicaciones científicas y artículos en revistas periódicas para una amplia audiencia durante gran parte del siglo XX.In this contribution, we present the artistic profile of the renowned Argentine paleontologist Carlos Rusconi, who made several artistic reconstructions of the extinct creatures as well as scientific drawings of the specimens throughout his career. In particular, his article “Animal Life in the Upper Tertiary of Buenos Aires” (1933) and his book “Extinct Animals of Mendoza and Argentina” (1967), which include several drawings by Paul Magne de la Croix, are icons of the science popularization of the paleontology in Argentina. In addition, we compile here the biographical data about the French artist Paul Magne de la Croix, as well as references to his contributions into the natural history. Magne de la Croix was a multifaceted person, who little is known about his personal life, while his immense work is disseminated in several contributions of different natures. In our understanding, the work of these two figures is the basis for the science popularization in South America and their art repeatedly occurs in books, scientific papers, and periodical articles for a broader audience during much of the twentieth century.Fil: Martinelli, Agustín Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Miñana, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Stratigraphy, fossil mammals, and age of the Eocene-Miocene volcano-sedimentary sequences of sierra Huantraico-sierra Negra and cerro Villegas (Neuquén Province, Argentina)

Se presentan los recientes avances en el conocimiento de la estratigrafía y la edad de las unidades volcanosedimentarias cenozoicas expuestas en el área de sierra de Huantraico-sierra Negra y cerro Villegas (Departamento Pehuenches, provincia del Neuquén, Argentina). Los análisis estratigráficos y de los restos fósiles hallados permiten reconocer y diferenciar seis unidades litoestratigráficas: a. ʻRodados Lustrosos’ (Eoceno Tardío-Oligoceno Temprano?), conformados por conglomerados gruesos texturalmente maduros (hasta 18 m de espesor) dispuestos sobre un marcado paleorrelieve labrado en sedimentitas preeocenas (fase diastrófica Incaica); b. Formación Rincón Escondido (nom. nov.) (Oligoceno Temprano-Oligoceno Tardío bajo), compuesta por depósitos fluviales de dominio psamítico asociado a un fuerte aporte piroclástico (31 m), se dispone y rellena el mismo paleorrelieve sobre el cual se sitúan los ʻRodados Lustrosos’; c. Formación Sierra Negra (nom. nov.) (Aquitaniano-Burdigaliano, Mioceno Temprano), suprayace a un nuevo paleorrelieve que llega a erosionar hasta depósitos del Cretácico Temprano (fase diastrófica Pehuenche); esta unidad puede subdividirse en el Miembro Filo Morado (hasta 250 m de basaltos alcalinos olivínicos, pirocalstitas, depósitos volcanoclásticos y sedimentarios volcanogénicos) y el Miembro Puesto Tillerías (nom. nov.) (hasta 600 m de coladas basálticas y andesíticas con intercalaciones de tobas y tufitas); d. Formación Pichi Tril (Burdigaliano tardío-Langhiano), conformada por cuerpos intrusivos de composición andesítica, cuyo emplazamiento se vincula a una deformación acaecida a fines del Mioceno Temprano (fase diastrófica Quechua); e. Formación Desfiladero Negro (Tortoniano Temprano), que conforma un conjunto de diques básicos que atraviesan al resto de la sucesión-una intrusión relacionada con deformación del Mioceno Tardío bajo; f. Formación La Tiza (Tortoniano tardío?-Mesiniano temprano, Mioceno Tardío), compuesta por hasta 85 m de depósitos conglomerádicos oligomícticos gruesos de baja madurez textural, originados a partir de la erosión de los cuerpos volcánicos y las coladas de la Formación Sierra Negra. La sucesión completa fue nuevamente deformada hacia finales del Mioceno (Mesiniano tardío). El hallazgo de restos de mamíferos fósiles en las formaciones Rincón Escondido (nom. nov.) y Sierra Negra (nom. nov.), sumadas a las dataciones radiométricas efectuadas por otros autores, han permitido calibrar geocronológicamente a las unidades volcanosedimentarias de esta región.We present here the recent advances in understanding the stratigraphy and age of the Cenozoic volcanic and sedimentary sequences exposed on the area of sierra Huantraico-sierra Negra and cerro Villegas (Pehuenches Department, Neuquén Province). Stratigraphic analyses and recovered fossil remains allow us to recognize and differentiate six litostratigraphic units: a. The 'Rodados Lustrosos' (Late Eocene-Early? Oligocene), composed of coarse-grained texturally mature conglomerates (up to 18 m thick), deposited on a strong paleorelief of eroded pre-Eocene sedimentary rocks (Inca diastrophic phase); b. The Rincón Escondido Formation (nom. nov.) (early Oligocene-lower Late Oligocene), composed of sandy fluvial deposits linked to a strong pyroclastic source (31 m), occupies and fills the same paleorelief on which the 'Rodados Lustrosos' lies; c. The Sierra Negra Formation (nom. nov.) (Aquitanian-Burdigalian, Early Miocene) overlies a younger paleorelief that erodes into deposits as old as Early Cretaceous (Pehuenche diastrophic phase); this unit can be subdivided into the Filo Morado Member (up to 250 m of olivine-alkaline basalts, pyroclastic rocks, and volcanogenic deposits) and the Puesto Tillerías Member (nom. nov.) (up to 600 m of basalts and andesitic rocks with interbedded tuffs and tuffites); d. The Pichi Tril Formation (late Burdigalian-Langhian) is composed of andesitic intrusive bodies linked to deformation that occurred by the end of the Early Miocene (Quechua diastrophic phase); e. The Desfiladero Negro Formation (early Tortonian) forms a set of basic dikes that cross the rest of the succession - an intrusion related to earliest Late Miocene deformation; f. The La Tiza Formation (late? Tortonian-early Messinian, Late Miocene), composed of up to 85 m of coarse-grained oligomictic conglomerates with low textural maturity, originated from the erosion of volcanic bodies and basaltic flows of the Sierra Negra Formation. This entire succession was again deformed at the end of the Miocene (late Messinian). The discovery of fossil mammals in the Rincón Escondido and Sierra Negra formations, together with radiometric dates provided by previous authors, have allowed a geochronologic calibration of the volcano-sedimentary units exposed in this region.Facultad de Ciencias Naturales y Muse