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A new basal notoungulate, Nanolophodon tutuca gen. et sp. nov., is described. This is represented by maxillary and dental fragments and by isolated teeth. The holotype and referred material were found at the “1968 Fissure” of the Itaborai Basin, Rio de Janeiro State, Brazil. This basin has been regarded as early Eocene in recent contributions. The generalized appearance and brachydonty of the studied specimens, together with the presence of certain typical traits (poorly developed entolophid, well-developed metacone column, etc.) indicate that N. tutuca can be considered among the group of genera traditionally known as henricosborniids, easily distinguishable from Typotheria by the absence of crista 1 and from Toxodontia by the absence of crista intermedia. It is also different from all other henricosborniids by a combination of characters, such as the presence of a long crochet, the development of two small cristae in the ectoloph, and the large paraconid, among others. In the context of a phylogenetic analysis performed, we do not find conclusive evidence about the synonymy between Itaboraitherium atavum and Othnielmarshia pristina. In turn, we question the reference of these forms as henricosborniids, based on the complex occlusal dental pattern observed in both cases. Finally, based on the observations made in the present study, we discuss the identification of the paraconid in notoungulates, which may be associated with some cusps located mesially to the metaconid and identified as pseudoparaconids in past studies.

We revise the mammal fossils from the Fray Bentos Formation previously assigned to Notoungulata, as well as some new remains recovered from levels cropping out in Corrientes Province (Argentina). In some cases, previous determinations have been completed to the species level, but others have been substantially modified, identifying different families. At present, identified taxa are: “Prohegetotherium” schiaffinoi (Hegetotheriidae), an undetermined interatheriid that is hypothesized as representing the upper teeth of Eopachyrucos ranchoverdensis, and Argyrohyrax proavus (Interatheriidae), cf. Archaeohyrax suniensis (Archaeohyracidae), cf. Mendozahippus fierensis (“Notohippidae”), a Leontiniidae indet., and some undetermined Notoungulata. The presence of Leontiniidae is based on the specimen CTES-PZ 7871, but those previously assigned to this family are herein discarded as such and reinterpreted (notohippid and undetermined taxon). The Mesotheriidae are discarded among the revised materials, but they are present in the Fray Bentos Formation in Corrientes Province with Trachytherus spegazzinianus (= Ameghinotherium curuzucuatiense). The revised sample presents affinities with the fauna from the type locality of the Fray Bentos Formation, in Uruguay, and the Deseadan assemblages from Quebrada Fiera (Mendoza Province, Argentina), Patagonia (Argentina), and Salla (Bolivia). These similarities are important from a paleobiogeographic point of view, especially by the recognition of cf. M. fierensis, a species only known from Mendoza up to now. Only the finding of new material from Fray Bentos Formation in Corrientes Province will allow us to corroborate these tentative determinations and a possible eastward extension of up-to-now exclusive taxa from Quebrada Fiera.

This contribution details new records of Notoungulata and Astrapotheria from the exposures of the Santa Cruz Formation in the Río Santa Cruz (Early-Middle Miocene; Province of Santa Cruz). The astrapothere Astrapotherium sp. Burmeister, the notoungulate toxodonts Homalodotherium sp. Flower, Nesodon sp. Owen and Adinotherium sp. Ameghino, and the typotheres Hegetotherium mirabile Ameghino, Interatherium sp. Ameghino, Protypotherium sp. Ameghino, P. attenuatum Ameghino, P. australe Ameghino and P. praerutilum Ameghino are recognized in the localities Barrancas Blancas and Segundas Barrancas Blancas. Nesodon imbricatus Owen was recorded in the former and Adinotherium ovinum (Owen) in the latter locality. The typothere Pachyrukhos moyani Ameghino was identified only in Segundas Barrancas Blancas, but with numerous specimens. Only the large ungulates Astrapotherium magnum (Owen) and Adinotherium sp. were recorded in Yaten Huageno. At a generic level, Barrancas Blancas and Segundas Barrancas Blancas only differ by the presence of Pachyrukhos Ameghino in the latter; at Yaten Huageno the Typotheria, Homalodotheriidae and Nesodon have not been recorded. The general faunal composition, including the larger samples from Barrancas Blancas and Segundas Barrancas Blancas, matches the record from the better-known Santacrucian localities from the Atlantic coast. This faunal similarity implies that similar environmental conditions prevailed in the two areas, indicating that the localities from Río Santa Cruz, as the Atlantic coastal localities, would have constituted a complex mosaic of open and closed habitats. Esta contribución involucra un reporte faunístico de los nuevos registros de Notoungulata y Astrapotheria provenientes de los yacimientos de la Formación Santa Cruz del Río Santa Cruz (Mioceno Temprano–Medio; provincia de Santa Cruz). El astrapoterio Astrapotherium sp., los notoungulados toxodontes Homalodotherium sp. Flower, Nesodon sp. Owen y Adinotherium sp. Ameghino, y los tipoterios Hegetotherium mirabile Ameghino, Interatherium sp. Ameghino, Protypotherium sp. Ameghino, P. attenuatum Ameghino, P. australe Ameghino y P. praerutilum Ameghino fueron reconocidos en Barrancas Blancas y Segunda Barrancas Blancas. Las especies Nesodon imbricatus Owen y Adinotherium ovinum (Owen) fueron identificados en la primera y en la segunda localidad, respectivamente. El tipoterio Pachyrukhos moyani Ameghino fue identificado únicamente en Segundas Barrancas Blancas, pero a través de numerosos ejemplares. Solo los ungulados de gran talla Astrapotherium magnum (Owen) y Adinotherium sp. fueron reconocidos en Yaten Huageno. A un nivel supraespecífico, Barrancas Blancas y Segundas Barrancas Blancas difieren por la presencia de Pachyrukhos Ameghino en la segunda, mientras que en Yaten Huageno los Typotheria, Homalodotheriidae y Nesodon no han sido identificados. La composición faunística general, incluyendo las grandes muestras provenientes de Barrancas Blancas y Segundas Barrancas Blancas, coincide con la registrada en las localidades Santacrucenses más conocidas de la costa Atlántica. Esta similitud faunística permite inferir, preliminarmente, similares condiciones ambientales, indicando que las localidades del Río Santa Cruz podrían haber constituido un complejo mosaico de ambientes abiertos y cerrados. Fil: Fernández, Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina. Universidad Nacional de Luján. Departamento de Ciencias Básicas; Argentina Fil: Muñoz, Nahuel Antu. Universidad Nacional de Luján. Departamento de Ciencias Básicas; Argentina. 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; Argentina

Thomas H. Huxley (1870) mentioned as Homalodotherium some fossils sent to him by Dr. Robert O. Cunningham, and sent these remains to William H. Flower to be described. Flower presented at the same time at the Royal Society of London (reception May 30, and presentation June 19, 1873) a short abstract (Flower, 1873) and a full description (Flower, 1874), which were, however, published with different date, being the abstract previous to the complete work. This fact gave place to subsequent nomenclatural changes because the author used a different generic name in the paper published in 1874, Homalodontotherium instead of Homalodotherium. Besides, Flower’s complete work is often referred to 1873 due to the date of presentation, but it was published in 1874. The abstract included a general comparison of the fossil, and the taxonomic name Homalodotherium cunninghami appears in the title. Fil: Seoane, Federico Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: 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; Argentina Fil: Scioscia, Cristina Luisa. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Cerdeño Serrano, Maria Esperanza. 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; Argentina

Henricosborniids are a group of South American native ungulates mainly found in Argentina (several Patagonian localities, Jujuy, and Mendoza), Brazil (Sao Jose de Itaborai), and Bolivia (Tiupampa) that have a biochron ranging from the Danian (Tiupampan SALMA) to the late Bartonian (Barrancan subage of the Casamayoran SALMA). The record of henricosborniids in Mustersan levels must be confirmed. The family includes the genera Henricosbornia, Peripantostylops, Othnielmarshia, Orome, and Simpsonotus. Their fragmentary fossil record, mainly limited to isolated teeth, has constrained their utility for obtaining phylogenetically useful characters; for that reason, only few taxa (i.e., Henricosbornia, Simpsonotus) are usually included in this type of analysis. Even though there is consensus about the basal position of the group within the order, the family is recovered as polyphyletic or, more commonly, paraphyletic. The analysis of specimens from the early Eocene of Las Violetas and Las Flores (Itaboraian SALMA), the oldest Patagonian localities yielding notoungulate remains, and Paso del Sapo, along with the implementation of both implied weighting and landmark information, allow us to discuss several features for use in henricosborniid phylogenetic analysis and identification: 1) ectoloph of the molars with well-marked paracone and metacone folds; 2) molars with crochet present, oblique to the ectoloph, with variable development; 3) triangular third upper molar, with poorly developed hypocone; 4) reduced trigonid with short paralophid; 5) entoconid more like an isolated cusp and not completely crested. Although useful, these characters need to be evaluated in a more exhaustive phylogenetic context.

Fil: Lopez, Guillermo Marcos. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Division Paleontologia Vertebrados; Argentina

We describe a new interatheriid notoungulate, Juchuysillu arenalesensis gen. et sp. nov., based on six partial upper and lower dentitions from the early to middle Miocene Nazareno Formation of southern Bolivia. A specimen is also referred to J. arenalesensis from the early middle Miocene (Langhian) locality of Cerdas, Bolivia (ca. 100 km to the northwest). The new species is distinguished by its very small size (ca. 15% smaller than Protypotherium minutum ) and the unique combination of shallow ectoloph sulci on P3-4, length of M1 > M2 > M3, trapezoidal upper molars, and absence of a buccal talonid sulcus on m3. A second, larger interatheriid species is present at Nazareno but is not represented by remains sufficiently complete for a more precise identification. A phylogenetic analysis indicates that J. arenalesensis represents a unique lineage within Interatheriinae that diverged after Protypotherium sinclairi but before Miocochilius anomopodus , Caenophilus tripartitus , Miocochilius federicoi , and several species of Protypotherium , including Protypotherium australe . Juchuysillu arenalesensis is one of two small (< ca. 3 kg) typotheres at Nazareno; its body mass is estimated at 1.1 kg. An updated faunal list for the Nazareno Formation includes 19 species of mammals pertaining to seven orders and 15 families; fragmentary turtle (Testudinidae?) and bird (Phorusrhacidae) remains are also present. The precise age of Nazareno Formation vertebrates is unknown, but the presence of at least three notoungulate species shared with Cerdas suggests a similar (~16–15 Ma) age for the fossil-bearing levels.

More than 40 remains of Tremacyllus Ameghino (Notoungulata, Hegetotheriidae, Pachyrukhinae) from the Province of La Pampa (Argentina) are analyzed. They were recovered from different outcrops of the late Miocene Cerro Azul Formation at Laguna Chillhué, Quehué, Telén, Salinas Grandes de Hidalgo, Estancia Ré, Bajo Giuliani, Barrancas Coloradas and Caleufú. During the late Miocene, pachyrukhines are represented by two genera, Tremacyllus and Paedotherium Burmeister. The present sample of Tremacyllus allows for the dental morphological variation to be evaluated, especially in lower and upper premolars. This study shows high variability in the diagnostic characters of two recognized species, T. impressus Ameghino (Pliocene-Pleistocene of the Pampean Region) and T. incipiens Rovereto (late Miocene of Catamarca). We interpret these differences to actually correspond to intraspecific variation and, consequently, propose their synonymy. T. impressus has priority over T. incipiens, and an emended diagnosis is provided. This nomenclatural action implies, in turn, the extension of the biochron of Tremacyllus impressus from the late Miocene to the Pleistocene. T. impressus differs from Paedotherium in its smaller size, post-incisive impressions extended beyond the level of P2 (even reaching the anterior margin of P3), M3 shorter or equal to M2, relatively shorter mandibular symphysis, and lower premolars not molariform and more imbricated. Within the studied sample, we identify several juvenile specimens that confirm the dental eruption pattern previously proposed for Tremacyllus based on fewer remains. Se analizan más de 40 restos de Tremacyllus Ameghino (Notoungulata, Hegetotheriidae, Pachyrukhinae) de la Provincia de La Pampa (Argentina). Se colectaron en diferentes afloramientos de la Formación Cerro Azul (Mioceno tardío) en Laguna Chillhué, Quehué, Telén, Salinas Grandes de Hidalgo, Estancia Ré, Bajo Giuliani, Barrancas Coloradas y Caleufú. Durante el Mioceno tardío, los paquiruquinos están representados por dos géneros, Tremacyllus y Paedotherium Burmeister. La muestra estudiada permite definir variaciones morfológicas dentales dentro de la muestra de Tremacyllus, especialmente en los premolares inferiores y superiores. El resultado muestra una amplia variabilidad en los caracteres previamente asumidos como diagnósticos en las dos especies reconocidas, T. impressus Ameghino (Plioceno-Pleistoceno de la Región Pampeana) y T. incipiensRovereto (Mioceno tardío de Catamarca). Se interpreta que las diferencias entre ellas corresponden a variaciones intraespecíficas y, por lo tanto, se propone su sinonimia, teniendo la prioridad de nombre T. impressus, y se proporciona una diagnosis enmendada. Esto implica, a su vez, la extensión del biocrón de Tremacyllus impressus, desde el Mioceno tardío hasta el Pleistoceno. Tremacyllus impressus difiere de Paedotherium en su menor tamaño, la presencia de impresiones postincisivas que exceden el nivel del P2 (alcanzando incluso la cara anterior del P3), el M3 igual o más corto que el M2, la sínfisis mandibular relativamente más corta y los premolares inferiores no molariformes y más imbricados. Dentro de la muestra estudiada, identificamos varios especímenes juveniles que confirman el patrón de erupción dentaria propuesto previamente para Tremacyllus a partir de pocos ejemplares. Fil: Sostillo, Renata. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina Fil: Cerdeño Serrano, Maria Esperanza. 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; Argentina Fil: Montalvo, Claudia Inés. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina

The Mesotheriinae records in the late Neogene of Argentina are mostly grouped in two genera: Typotheriopsis and Pseudotypotherium. Both taxa were poorly diagnosed and/or based on juvenile specimens. Traditionally, the dental feature considered to distinguish them is the presence of a lingual groove in the last upper premolar. Other features were mostly dismissed or considered non-informative at a generic level. Based on this, we reanalyzed dental features in Typotheriopsis and Pseudotypotherium samples to evaluate their relevance in a taxonomic framework. This study brings new qualitative and quantitative tools to appraise diagnostic features present in fossil fragments and isolated dental mesotheriine pieces.

Recent fieldtrips led to the discovery of new specimens of a recently described interatheriid from Northwestern Argentina, Antofagastia turneri. These new specimens show some intraspecific variation regarding size and certain coronal features. Additionally, two fossil remains bearing lower teeth, one of them previously referred as Punapithecus minor, were analyzed. Overall size and some occlusal traits indicate that this material may be considered as closer to Antofagastia than to Punapithecus. The new specimens bring new information regarding intraspecific and ontogenetic variation, which represents a valuable tool to assess diagnostic features present in fossil fragments and isolated dental pieces. Fil: Garcia Lopez, Daniel Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina

South American native ungulates include several extinct lineages that evolved within the context of South American Cenozoic geographic isolation. By the late–early Miocene Santacrucian, the orders Notoungulata, Litopterna, and Astrapotheria were differentiated. Recent ecomorphological studies highlighted complex functional patterns between their habitat/diet and hypsodonty. In order to understand these relationships in an evolutionary context we used geometric morphometrics methods (27 3-D landmarks) to evaluate the morphological integration of two of the primary functional units of the mandible: the alveolar region and the ascending ramus. Principal component analyses (PCA) and two blocks Partial Least Squares analyses (PLS) were used to explore the patterns of variation and covariation between these two modules. The main variation in shape is related to the robusticity and curvature of the mandibular corpus, and the relative size of the angular and coronoid process. The PLS analyses show a very strong morphological integration within the Litopterna, but a pattern of modularity in the Notoungulata. There is a common pattern of covariation in Astrapotheria and Litopterna, which might be due to similar constraints. The different covariation patterns in notoungulates with respect to litopterns are in concordance with both the taxonomic and morphological diversity of the clades, particularly in the typotheres. The modularity present in notoungulates could have allowed specializations in each module of the mandible, related to crown height or muscle attachments, without a high morphological constrain. This could have resulted in their high morphological diversity, in contrast with the more conservative morphology present in litopterns., Los ungulados nativos de América del Sur incluyen varios linajes extintos que evolucionaron en el contexto de aislamiento geográfico del Cenozoico sudamericano. Durante el Santacrucense (Mioceno temprano), los órdenes Notoungulata, Litopterna y Astrapotheria ya estaban diferenciados. Los estudios ecomorfológicos recientes destacaron patrones funcionales complejos entre hábitat/dieta e hipsodoncia en estos grupos. Se analizan estas relaciones en un contexto evolutivo, utilizando métodos morfogeométricos (27 landmarks 3-D) para evaluar la integración morfológica de dos de las unidades funcionales principales de la mandíbula: región alveolar y rama ascendente. Para explorar los patrones de variación y covariación entre estos dos módulos, se utilizaron Análisis de componentes principales (PCA) y Análisis de mínimos cuadrados parciales de dos bloques (PLS). La variación principal de forma está relacionada con la robustez y la curvatura del cuerpo mandibular y el tamaño relativo de los procesos angular y coronoides. Los PLS muestran una integración morfológica muy fuerte en Litopterna y un patrón de modularidad en Notoungulata. Existe un patrón común de covariación en Astrapotheria y Litopterna que podría deberse a restricciones similares. Los diferentes patrones de covariación en notoungulados con respecto a los litopternos están en concordancia con la diversidad taxonómica y morfológica de los clados, particularmente en los tipoterios. La modularidad presente en Notoungulata habría permitido especializaciones en cada módulo de la mandíbula, relacionadas con la altura de la corona o las inserciones musculares, sin una alta restricción morfológica. Esto podría haber resultado en su alta diversidad morfológica, en contraste con la morfología más conservadora presente en Litopterna. Palabras clave. Notoungulata. Litopterna. Santacrucense. Morfometría Geométrica, Facultad de Ciencias Naturales y Museo (FCNM)

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 res...

The Order Notoungulata is a large group of endemic mammals widespread throughout the Cenozoic of South America. Among them, the Family Homalodotheriidae is one of the less abundant and diverse, and geographically more restricted. Its record ranges from early Oligocene to late Miocene, but only a few genera were described, mainly known from Patagonia. This paper deals with the first homalodotheriid remains recovered from Deseadan levels outside Patagonia. The material comes from Quebrada Fiera, a late Oligocene locality in southern Mendoza Province (Argentina), and mainly consists of postcranial elements. A comparative study lead to its placement in the Patagonian genus Asmodeus Ameghino, but with some significant differences from Asmodeus osborni Ameghino. Thus a new species —Asmodeus petrasnerus sp. nov.— is proposed for the taxon from Mendoza. It is characterized by: calcaneum with a subtriangular navicular facet, ectal facet with concave medial border, and not projected anterodistal end; astr...

The present paper deals with the description of the first remains of the Family Mesotheriidae in the Quebrada Fiera locality. The fauna from Quebrada Fiera comes from sediments nowadays considered to represent the base of the Agua de la Piedra Formation. The recovered faunal assemblage includes typical elements of the Deseadan Age (late Oligocene), shared with both Patagonian and lower latitude associations (e.g., Salla, Bolivia). A unique specimen of Mesotheriidae has been recovered after several field seasons since 2006. It is a palatal portion in two fragments, one bearing the I1 and the other with left P4-M2 and right M1-2. Morfological and metrical features of this material reveal a taxon much closer to the Patagonian mesotheriid species Trachytherus spegazzinianus than to the Bolivian taxa, T. alloxus and T. subandinus, and it is determined as Trachytherus cf. T. spegazzinianus. Its presence in Mendoza fills a gap in the expected geographical distribution of this mesotheriid, as it was also recorded in the Bolivian site of Lacayani. The scanty record of mesotheriids in Quebrada Fiera contrasts with Salla and Patagonian localities. Fil: Cerdeño Serrano, Maria Esperanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

Until the discovery of the genus Punahyrax (Geste Formation) in different localities of Catamarca and Salta provinces, “archaeohyracids” were unknown in northwestern Argentina. Here we analyze the record of these notoungulates in the region through specimens known for the Geste Formation and new remains recovered from the lower levels of the Quebrada de Los Colorados Formation, assessing their diversity and significance in the context of the pre-Deseadan radiation of Typotheria. We identify three “archaeohyracid” morphotypes for Barrancan levels and four for Mustersan levels in northwestern Argentina, implying the possible presence of as much as seven “archaeohyracid” taxa in the region for the last third of the Eocene, and illustrating a striking diversity, especially considering the scarce pre-Tinguirirican record known until now. These new records underline the faunal differences of the Geste and Quebrada de los Colorados formations regarding the highly fossiliferous Lower and Upper Lumbrera formations. In this sense, although the existence of a sample bias should not be completely dismissed, the possibility of important biogeographic barriers acting in the area by the late middle Eocene needs to be analyzed with independent evidence. The record of Pseudhyrax eutrachytheroides in northwestern Argentina represents the first notoungulate taxon common between this region and typical Patagonian localities and represents a useful and presumably reliable new basis for the assignment of a Mustersan age for the middle section of the Geste Formation

The family Isotemnidae, now considered paraphyletic by some, is composed of the most basal members of the suborder Toxodontia. They were moderate to large, plantigrade or semidigitigrade mammals, with features related to weight bearing. Several isolated postcranial remains from the Sapoan Fauna (early Eocene) have been referred to one of the earliest isotemnid genera, Isotemnus . This is the largest notoungulate genus found in the Sapoan Fauna, and isotemnid remains can be distinguished from those of similarly-sized notostylopids. Here, the anatomy of these remains is compared with those of later isotemnids, Thomashuxleya and Periphragnis . Isotemnus was one of the smallest isotemnids (around 50 kg, inferred from the astragalus) while Thomashuxleya and Periphragnis were four times larger (~200 kg). Thomashuxleya and Periphragnis share features not present in other Eocene notoungulates such as Notohippidae or Notostylopidae, including: a distal humerus with a sharp, salient medial trochlear crest; radial bicipital tuberosity not present or barely insinuated; astragalus with wide and low trochlea, short neck, and variable nuchal crest; and a calcaneus with a rectangular fibular facet, half the length of the ectal facet, and an unusually thick sustentaculum. Isotemnus shares some of these features, but in other aspects, it is more similar to smaller typotherian taxa; the astragalar neck is better developed, and a crest is present on the calcaneal body that is absent in Periphragnis . These differences could be due to the smaller size of Isotemnus and its earlier divergence from other toxodontians and could help elucidate the most basal morphology of Notoungulata.

A description of Colbertia lumbrerense Bond (Mammalia, Notoungulata) is presented. This species is recorded in levels of the Lumbrera Formation (Eocene) in northwestern Argentina. Several specimens were collected; yet its cranial osteology has not been studied in detail. The new description provided herein is based on five specimens, including the type specimen. The external surface of the posterior zone of the skull in this species shows a generalized notoungulate morphology. The development of certain elements (external auditory meatus, meatal crest, epitympanic sinus) is similar to that observed in other Paleogene notoungulates such as Simpsonotus Pascual, Vucetich, and Fernandez; Brachystephanus Simpson, Minoprio, and Patterson; and Xenostephanus Simpson, Minoprio, and Patterson. In spite of this generalized arrangement, the skull shows some distinctive features, particularly in the petrosal. Some traits of this bone are shared with Dolichostylodon saltensis Garcia Lopez and Powell, a notoun...

Biomechanical and morphofunctional study of the appendicular skeleton of Homalodotherium Flower 1873 (Mammalia, Notoungulata). Homalodotherium (Santacrucian- Friasian; early Miocene) is the best represented genus of the Family Homalodotheriidae (Notoungulata). It was proposed as a digging form, browser on trees in food habits, and with potential for adopting bipedal posture. The appendicular skeleton is studied morphometrical and biomechanically, considering proportions, principal bone accidents, and muscular insertions, comparing with extant mammals. Bone elements of the appendicular skeleton are described, the musculature reconstructed, and 10 morphometric measurements used for calculating eight functional indices. Indices include deltoid proportion and epicondilar development of the humerus, ulnar robustness and olecranon proportion, femoral and tibial robustness, and distal extension of the fore and hind limbs. The forelimb preponderates force development in humeral flexion and protraction of...

Three orders of South American extinct native ungulates are recorded from the Santa Cruz Formation along the Atlantic coast of Patagonia: Notoungulata (Adinotherium Ameghino, Nesodon Owen, Interatherium Ameghino, Protypotherium Ameghino, Hegetotherium Ameghino, and Pachyrukhos Ameghino), Litopterna (Theosodon Ameghino, Anisolophus Burmeister, Tetramerorhinus Ameghino, Diadiaphorus Ameghino, and Thoatherium Ameghino), and Astrapotheria (Astrapotherium Burmeister). An ecomorphological study based on geometric morphometrics of the masticatory apparatus was performed. The reference sample included 618 extant specimens of the orders Artiodactyla, Perissodactyla, Hyracoidea, and Diprotodontia. Thirty six cranial and 27 mandibular three-dimensional landmarks were digitized. Allometric scaling, principal component analyses, and phylogenetic generalized estimating equations on the cranium and mandible were preformed. Analyses of cranial shape show strong phylogenetic constraints, whereas the mandibular analyses show a functional pattern related to habitat/ diet and hypsodonty. The extant brachydont ungulates from closed habitats show a more elongated and narrower mandibular symphysis with a lower mandibular corpus, than hypsodont, open habitat species. The latter have short symphyses with a high, curved mandibular corpus. This morphological pattern was also present among Santacrucian ungulates, allowing characterization of notoungulates mainly as open habitats dwellers, with some taxa foraging on grass (Protypotherium, Interatherium), and others on grass and leaves (Hegetotherium, Pachyrukhos, and Adinotherium), depending on the availability. Nesodon may have dwelled in mixed habitats and had a mixed feeding behavior, while small proterotheriids (Anisolophus and Thoatherium) may have fed predominantly on dicotyledonous plants. The remaining litopterns (Tetramerorhinus, Diadiaphorus, and Theosodon) and Astrapotherium may have foraged in closed habitats and fed on dicotyledonous plants. En la Formación Santa Cruz a lo largo de la costa atlántica patagónica se registran tres órdenes de ungulados nativos sudamericanos: Notoungulata (Adinotherium Ameghino, Nesodon Owen, Interatherium Ameghino, Protypotherium Ameghino, Hegetotherium Ameghino y Pachyrukhos Ameghino), Litopterna (Theosodon Ameghino, Anisolophus Burmeister, Tetramerorhinus Ameghino, Diadiaphorus Ameghino y Thoatherium Ameghino) y Astrapotheria (Astrapotherium Burmeister). Se realizaron estudios ecomorfológicos mediante morfometría geomé- trica del aparato masticatorio. Se incluyeron 618 especímenes actuales de los órdenes Artiodactyla, Perissodactyla, Hyracoidea y Diprotodontia como marco de referencia. Se utilizaron 36 landmarks tridimensionales craneanos y 27 mandibulares. Se realizaron análisis alométricos, componentes principales y ecuaciones de estimación generalizada con control filogenético de cráneo y mandíbula. Los análisis cranianos estuvieron más condicionados por la filogenia, mientras que la mandíbula muestra un patrón funcional complejo entre hábitat/dieta e hipsodoncia. Los ungulados actuales de ambientes cerrados y braquiodontes poseen mandíbulas con la sínfisis alargada y estrecha y cuerpo mandibular más bajo que las especies de ambientes abiertos e hipsodontes, las cuales poseen mandíbulas con la sínfisis corta y cuerpo mandibular alto y curvado. Este patrón morfológico se repite entre los ungulados santacrucenses, permitiendo ubicar a los Notoungulata principalmente en ambientes abiertos. Algunos taxones forrajearían en pasturas (Protypotherium, Interatherium), otros lo harían en pasturas o hierbas (Hegetotherium, Pachyrukhos y Adinotherium), dependiendo de la disponibilidad. Nesodon habitaría ambientes mixtos y tendría dieta mixta, mientras que los proterotéridos pequeños (Anisolophus y Thoatherium) se alimentarían predominantemente de dicotiledóneas. Los Litopterna restantes (Tetramerorhinus, Diadiaphorus y Theosodon) y Astrapotherium forrajearían en ambientes cerrados, alimentándose sobre dicotiledóneas. Fil: Cassini, Guillermo Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina. Universidad Nacional de Luján. Departamento de Ciencias Básicas; Argentina

El extenso aislamiento temporal y geográfico que mantuvo incomunicada a América del Sur durante gran parte del Cenozoico promovió el desarrollo de una fauna terrestre exclusiva de esta región. Dentro de esta fauna, se incluye a los “ungulados nativos sudamericanos” que tuvieron una amplia distribución en Argentina. Durante el Mioceno Tardío, estos ungulados se encuentran representados por los órdenes Litopterna y Notoungulata. En la provincia de Entre Ríos, procedentes del “Mesopotamiense” o “Conglomerado osífero”, base de la Formación Ituzaingó, se encuentran dos familias de litopternos, Proterotheriidae y Macraucheniidae, y dos de notoungulados, Toxodontidae e Interatheriidae. El estudio de estos grupos ha sido abordado por diferentes autores desde fines del siglo XIX hasta la actualidad. El objetivo de este capítulo es resumir los principales antecedentes sobre los taxones entrerrianos y presentar el estado actual del conocimiento de la historia biogeográfica de esta fauna particular sudamericana. The extensive temporal and geographical isolation of South America during most of the Cenozoic allowed the development of an exclusive terrestrial fauna in this region. Within this fauna are the so-called South American native ungulates, which are widely spread in Argentina. During the late Miocene, these ungulates were represented by the orders Litopterna and Notoungulata. In Entre Ríos Province, two litoptern (Proterotheriidae and Macraucheniidae) and two notoungulate families (Toxodontiidae and Interatheriidae) are recorded from the “Mesopotamiense” or “Conglomerado osífero”, base of the Ituzaingó Formation. The study of these groups has been addressed by different authors since the end of the XIX century. The aim of this chapter is to summarize the main information on the Entre Ríos taxa and to show the current state of knowledge on the biogeographic history of this South American particular fauna. Fil: Schmidt, Gabriela Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina Fil: Cerdeño Serrano, Maria Esperanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

A description of Colbertia lumbrerense Bond (Mammalia, Notoungulata) is presented. This species is recorded in levels of the Lumbrera Formation (Eocene) in northwestern Argentina. Several specimens were collected; yet its cranial osteology has not been studied in detail. The new description provided herein is based on five specimens, including the type specimen. The external surface of the posterior zone of the skull in this species shows a generalized notoungulate morphology. The development of certain elements (external auditory meatus, meatal crest, epitympanic sinus) is similar to that observed in other Paleogene notoungulates such as Simpsonotus Pascual, Vucetich, and Fernández; Brachystephanus Simpson, Minoprio, and Patterson; and Xenostephanus Simpson, Minoprio, and Patterson. In spite of this generalized arrangement, the skull shows some distinctive features, particularly in the petrosal. Some traits of this bone are shared with Dolichostylodon saltensis García López and Powell, a notoungulate recorded in upper levels of the same formation. The morphology described in this study is consistent with recent phylogenetic analyses of Paleogene notoungulate taxa that place C. lumbrerense in a basal position. Resumen. Osteología del Basicráneo de Colbertia Lumbrerense Bond (Mammalia: Notoungulata). Se presenta una descripción de la anatomía craneal de Colbertia lumbrerense Bond (Mammalia: Notoungulata). Esta especie ha sido registrada en niveles de Formación Lumbrera (Eoceno) del noroeste argentino y, aunque se han colectado varios individuos, su osteología craneana no ha sido estudiada en detalle. Esta descripción está basada en cinco individuos, incluyendo el holotipo de la especie. La zona posterior del cráneo en esta especie muestra rasgos generalizados para los notoungulados. El desarrollo de ciertos elementos (meato auditivo externo, cresta meatal, senos epitimpánicos) es similar al observado en otros notoungulados paleógenos como Simpsonotus Pascual, Vucetich y Fernández, Brachystephanus Simpson, Minoprio y Patterson y Xenostephanus Simpson, Minoprio y Patterson. A pesar de esta morfología generalizada, el cráneo muestra peculiaridades significativas, como el petroso. Algunas características de este hueso son compartidas con Dolichostylodon saltensis García López y Powell, un notoungulado registrado en niveles superiores de la misma formación. Las observaciones llevadas a cabo en este estudio son consistentes con análisis filogenéticos recientes de taxones paleógenos que ubican a C. lumbrerense en una posición basal. Fil: Garcia Lopez, Daniel Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Cátedra de Paleozoología; Argentina

A new representative of the family Oldfieldthomasiidae from Northwestern Argentina, Dolichostylodon saltensis gen. et sp. nov., is described. The material was found in the Lumbrera Formation, above the “Faja Verde II”, at El Simbolar, Guachipas Department, Salta Province, Argentina. Dolichostylodon saltensis is defined by the following features: deciduous and permanent upper teeth similar to Ultrapithecus rutilans Ameghino, 1901, but with more triangular dP, more prominent paracone, without mesiolabial fossette and with dP3 presenting well developed metaloph. Upper molars with prominent parastyle and metastile. Column of metacone wider than in Colbertia lumbrerense Bond, 1981. Mesiolabial fossette absent, distolabial fossette relatively wide and shallow. Well developed and curved crochet, surrounding the distolabial fossette. Wide distal cingulum. Hypocone reduced in relation to the protocone. Labial sulcus not very pronounced. Lower molars with expanded entoconid, located close to the hypoconulid and presenting a reduced sulcus between both. Talonid valley deeper than in C. lumbrerense. This discovery constitutes the second species of Oldfieldthomasiidae for this Formation and the third for Northwest Argentina. Other materials assigned to Oldfieldthomasiidae have been reported from Antofagasta de la Sierra Catamarca Province) but they were referred to the genus Colbertia Paula Couto, 1952. This species shows morphological similarities with Ultrapithecus rutilans, of the “Barrancan” (Casamayoran) of Patagonia. Dolichostylodon saltensis seems to have closer relationship with the patagonic forms than with the non-Patagonian species of Oldfieldthomasiidae, despite its brachydont teeth. Fil: Powell, Jaime Eduardo. Universidad Nacional de Tucuman. Facultad de Cs.naturales E Instituto Miguel Lillo. Instituto de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Garcia Lopez, Daniel Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina

La familia Notohippidae Ameghino 1895 comprende a notoungulados que se registran desde el Eoceno Inferior (Bond y López, 1993) al Mioceno inferior de América del Sur (Reig, 1981; Cifelli, 1985, 1993; Bond, 1986; Shockey, 1999) y que a lo largo de su evolución desarrollaron formas con dentición hipsodonte, convergente con la de los équidos norteamericanos, por lo que se los considera como uno de los grupos de pastadores sudamericanos más antiguo (Bond, 1986). Fil: Marani, Hernán Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina Fil: Dozo, Maria Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina