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

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

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

A new thylacosmilid (Mammalia, Metatheria, Sparassodonta) from the Miocene of Patagonia, Argentina

A new genus and species, Patagosmilus goini, of the family Thylacosmilidae (Mammalia, Metatheria, Sparassodonta) is described here. The new taxon is based on a single specimen collected from the west margin of the Río Chico, in Río Negro Province, Argentina, from the middle Miocene Colloncuran SALMA. Until now, two formally recognized species were encompassed in the family Thylacosmilidae: Thylacosmilus atrox, from the late Miocene-late Pliocene Huayquerian to Chapadmalalan SALMAof Argentina and probably Uruguay; and Anachlysictis gracilis, from the middle Miocene Laventan SALMA of Colombia. Recognition of the Patagonian taxon, Patagosmilus, provides new anatomical data, likely to be included in future phylogenetic analyses. The overall morphology of Patagosmilus suggests that it has a more generalized anatomy than Thylacosmilus. The dental morphology suggests the new Patagonian taxon was probably closer to Thylacosmilus than Anachlysictis. Saber-tooth thylacosmilids have several autapomorphic features in the skull that differentiate them from other sparassodonts, including the delayed replacement or non-replacement of the deciduous last premolar.Fil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Carlini, Alfredo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentin

New remains of Astraponotus (Mammalia, Astrapotheria) and considerations on Astrapothere cranial evolution

Astraponotus Ameghino, 1901, the only valid Mustersan (late Eocene) astrapothere, typifies the Ameghino’s ‘‘Capas Astraponotenses’’. This taxon is traditionally interpreted as structurally ancestral to all the Oligocene– Miocene astrapotheriids. However, it was imperfectly known: only isolated teeth and very partial mandibles have hitherto been described. In this contribution we provide the first description of the skull, mandible, and complete dentition of Astraponotus based on new materials from the Gran Hondonada and other Mustersan localities in central Patagonia, Argentina. The features observed in the dentition of Astraponotus are intermediate between the Casamayoran (middle Eocene) and the Oligocene–Miocene astrapotheres in the degree of hypsodonty, reduction of the dental formula, and development of accessory occlusal elements. Concordantly, the skull retains some plesiomorphies, also observed in Trigonostylops, whereas the auditory region and the basicranium are much closer to those of Parastrapotherium, Astrapotherium, and Granastrapotherium. On the other hand, the skull of Astraponotus differs from all known astrapotheres by the disproportioned height and narrowness of the braincase, the extreme reduction of the nasals and the premaxillaries, the absence of anteorbital rim, and the reduction of the frontal region. Some of these features represent cranial specializations exactly opposite to that of Astrapotherium. These characters look astonishingly derived for an Eocene astrapothere, suggesting that extreme cranial specializations occurred independently during the evolution of the order, and that Astraponotus represents a distinctive lineage from that of Astrapotherium and other Miocene forms.Fil: Kramarz, Alejandro Gustavo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Bond, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Forasiepi, Analia Marta. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

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

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