The choanal anatomy of the Sebecus icaeorhinus Simpson, 1937 and the variation of the palatine shape in notosuchians (Crocodyliformes, Mesoeucrocodylia)

Sebecidae is a clade of large carnivorous crocodyliforms that thrived in the Cenozoic and is the only lineage of the diverse and terrestrial group Notosuchia that survived the end-Cretaceous mass extinction event. Sebecus icaeorhinus is the best-known taxon from this clade, both in terms of its cranial and postcranial anatomy (known primarily from the holotype and specimen MPEF-PV 1776, respectively). Additional material represented by a partial skull (MMP 235) is the only specimen that has preserved a complete choanal region. We describe new information from this specimen based on an X-ray computed tomography and identify through comparisons with other taxa a large degree of variability in the palatal anatomy within Sebecidae, in particular in the shape and extension of the palatine (the bone that defines the anterior position and shape of the secondary choana). We quantify variation in the shape of the palatine bone of sebecids through a 2D morphogeometric analysis within the context of notosuchian crocodyliforms. Although traditional accounts of palatal evolution in crocodyliforms linked variation of this structure to the adaptation to the aquatic environment, our analysis allows recognition of eight palatine morphotypes among terrestrial crocodyliforms with very distinct paleoecological traits, including carnivorous, omnivorous, and possibly herbivorous taxa. Furthermore, we show that sebecids had a higher morphological disparity in the choanal region than other terrestrial groups of Notosuchia, underscoring the importance of this region for comparative, morphofunctional, and phylogenetic studies.Fil: Bravo, Gonzalo Gabriel. 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; ArgentinaFil: Pol, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Armella, Matías Alberto. 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; ArgentinaFil: Gomez, Kevin Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentin

Postcranial remains of basal typotherian notoungulates from the eocene of Northwestern Argentina

Notoungulates represent the most taxonomically diverse and temporally and geographically widespread group among South American native ungulates. Here, we analyze anatomical and systematic aspects of proximal tarsal bones recovered from the Lower and Upper Lumbrera formations (middle and late middle Eocene) in northwestern Argentina. We provide detailed descriptions, comparisons, and infer foot stances and range of movements for the taxa implicated. Material studied includes astragali belonging to the oldfieldthomasiid Colbertia lumbrerense (Lower Lumbrera Formation), a set of proximal tarsals referred as Typotheria indet. (Lower Lumbrera Formation), and tarsals (also including navicular and cuboid) of the informal taxon “Campanorco inauguralis” (Upper Lumbrera Formation). The comparison of the tarsals of Colbertia lumbrerense (middle Eocene of Argentina) with Colbertia magellanica (early Eocene of Brazil) reveals several differences including variations on the development and arrangement of articular facets, and the size of the dorsal astragalar foramen in the Argentinean species. The specimen of Typotheria indet. shows morphological affinities with basal interatheriid taxa. However, its larger size contrasting with the overall small body sizes of Eocene interatheriids precludes an indisputable taxonomic assignment. Concerning “Campanorco inauguralis”, our observations indicate that there is no morphological evidence for a close phylogenetic relationship with Mesotheriidae. It presents a “reversed alternating tarsus” condition, which is also observed in Leontiniidae, “Notohippidae”, Toxodontidae, and some typotherians. However, the spectrum of singularities exhibited by this form precludes the assessment of its relationships in the context of the Paleogene radiation of Typotheria and it is necessary to extend the comparison to Eocene notoungulates. Finally, in a morphofunctional context a plantigrade foot posture is inferred for the specimens here reported. These observations have the potential to provide functional proxies for paleoecological reconstructions to be applied to the study of the early radiation of these notoungulate faunas.Fil: Armella, Matías Alberto. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: 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; ArgentinaFil: Babot, María Judith. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Deraco, Maria Virginia. 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; ArgentinaFil: Herrera, Claudia Marcela Reina. Fundación Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Saade, Luis Sebastián. 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; ArgentinaFil: Bertelli, Sara Beatriz. 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; Argentin

Tooth Size Variation in Assemblages of Tremacyllus (Hegetotheriidae, Notoungulata): Insights into Geographical Gradients, Systematics, and Sexual Dimorphism

Tooth size variation within fossil assemblages can be associated with intra- or interspecific variation, functional, developmental, and geographical factors, and/or sexual dimorphism. Understanding these sources of variation is necessary to develop diagnoses for fossil mammals, where teeth are usually the most frequent remains. Tremacyllus (Ameghino, 1891) (Hegetotheriidae, Notoungulata) is a genus of small-sized herbivorous mammals abundant in late Miocene to Pliocene outcrops of southern South America. Its simplified, euhypsodont dentition and size variability have hampered systematics studies and led, for instance, to an overestimation of the number of species. I analyzed tooth size variations within assemblages of Tremacyllus in a quantitative framework to test three hypotheses: (1) magnitudes of size variation are different among tooth loci and assemblages; (2) tooth size follows a geographical pattern within the analyzed sample (Bergmann’s rule), but is also associated with taxonomy; and (3) there is a correlation between size variation and sexual dimorphism reflected in distinguishable subgroups. Results indicate that patterns of variation might be associated with eruption time and/or functional position. Northwestern forms are larger than southwestern-Pampean ones, not conforming to Bergmann’s rule but revealing a strong influence of latitude. Size differences between assemblages agree with dental features that distinguish T. incipiens and T. impressus, allowing expanded species diagnoses. Two size subgroups might reflect sexual dimorphism in the absence of biostratigraphic or morphological differences between them. This interpretation indicates that northwestern specimens referred to T. diminutus should be referred to T. incipiens.Fil: Armella, Matías Alberto. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Inst. de Estratigrafía y Geología Sedimentaria Global; Argentina. 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; Argentin

Sistemática, bioestratigrafía y paleobiogeografía de los notoungulados del Neógeno del Noroeste Argentino

Los niveles fosilíferos del Neógeno continental del Noroeste de Argentina (NOA) son singulares por su gran extensión y representan el lapso desde aproximadamente 11 a 2.5 Ma (Mioceno tardío-Plioceno tardío). Históricamente, las unidades allí representadas han sido reconocidas por ser portadoras de una fauna muy numerosa y diversa de vertebrados fósiles, particularmente mamíferos. Entre estos, los miembros del orden Notoungulata representan uno de los elementos más conspicuos y desde el siglo XIX, expediciones realizadas a los afloramientos de la región brindaron excelentes fósiles de los mismos. Sin embargo, a pesar de que el conocimiento del grupo en el neógeno de América del Sur ha aumentado considerablemente en las últimas dos décadas, los notoungulados del NOA han sido escasamente incluidos en estudios sistemáticos, filogenéticos, bioestratigráficos y paleobiogeográficos generales. En este marco, la presente tesis se centra en los representantes de tres familias de Notoungulata (Toxodontidae, Mesotheriidae y Hegetotheriidae) provenientes de diferentes afloramientos del Neógeno de la región.Prospecciones realizadas en diversas localidades de las provincias de Jujuy, Salta, Tucumán, Catamarca y Santiago del Estero permitieron el hallazgo de un gran número de especímenes inéditos con buena procedencia estratigráfica y detalladamente georreferenciados. De esta manera, este estudio abarca tanto nuevos registros como materiales previamente determinados. Los afloramientos prospectados corresponden a unidades agrupadas en dos grandes provincias geológicas: Sierras Pampeanas Noroccidentales (afloramientos mejor conocidos y con mayores registros fósiles) y Llanura Chaqueña, para la cual se brindan los primeros registros de notoungulados.Dentro de la familia Toxodontidae, se reconocen restos aff. ?Andinotoxodon?. Dicho taxón se encuentra informalmente establecido por lo cual se realiza una síntesis de la problemática. Por otra parte, se identifica un nuevo representante del género Xotodon (X. caravela), para el cual se realiza un análisis filogenético que permite recuperar una sinapomorfía para el género y proponer una enmienda a su diagnosis. Finalmente se menciona el primer registro de los géneros Ocnerotherium y Pisanodon para el NOA, ampliando notablemente la diversidad del grupo para la región.Respecto a los Mesotheriidae, se identifican nuevos rasgos útiles para diferenciar el género Typotheriopsis de Pseudotypotherium, importantes para la identificación de restos incompletos o no asociados. Se realiza una descripción detallada de nuevos materiales correspondientes a diferentes especies de dichas entidades. Se reconocen formas con rasgos intermedios entre taxones neógenos de Argentina y Bolivia. Se identifican restos referidos a Plesiotypotherium cf. P. achirense, los cuales representan el primer registro del género para Argentina. Por otro lado, análisis paleobiológicos vinculados con la dieta de Mesotheriidae permiten reconocer tres morfotipos asociados a la selección del alimento. Se observa una fuerte correlación entre la historia evolutiva de los Mesotheriidae y los morfotipos identificados, la cual incluye aspectos de tamaño, relaciones filogenéticas y distribución temporal de los diferentes taxones.En cuanto a la familia Hegetotheriidae, se dan a conocer nuevos registros de Hemihegetotherium achataleptum. A su vez, se describen materiales atribuibles a Hemihegetotherium cf. H. achataleptum y Hemihegetotherium sp. que muestran ciertas particularidades relacionadas con el tamaño. Respecto a la subfamilia Pachyrukhinae, se revalida a Tremacyllus incipiens como especie del género. A su vez, se reconsideran hipótesis previas que establecen un endemismo de la especie para el NOA. Por otro lado, se describen materiales completos asignados a Paedotherium typicum y P. bonaerense, taxones registrados por primera vez en la región.En base al registro actual los notoungulados de mayor tamaño (i.e., toxodóntidos) muestran una distribución diferencial, encontrándose poblaciones distintas hacia ambos lados de las principales sierras (i.e., Cumbres Calchaquíes y Sierras del Aconquija). Por su parte, los grupos de menor talla (i.e., hegetotéridos) presentan una distribución más amplia, con taxones en común para ambos lados de las cadenas montañosas. Hasta el momento, los hallazgos de mesotéridos se concentran en los afloramientos intermontanos del oeste. En estos valles se registran formas similares a faunas de Bolivia y Chile. Por otro lado, en las áreas de llanura del NOA, los mesotéridos están escasamente representados. Esto último puede deberse a un sesgo en el muestreo, dado el reciente interés por los afloramientos de llanura de la región.En base a los estudios realizados se confirma que la diversidad de notoungulados del Noroeste Argentino durante el Mioceno-Plioceno es considerablemente mayor que la establecida previamente. A su vez, para algunos grupos (i.e., Hegetotheriidae y Toxodontidae) la discrepancia inferida respecto a la composición faunística del Neógeno del NOA en relación al resto de Argentina es atribuida a un sesgo en el registro.ABSTRACTThe fossil levels of the Neogene continental outcrops of Northwestern Argentina (NWA) are well-known by their great extension and represent a span from approximately 11 to 2.5 Ma (late Miocene-late Pliocene). Historically, these units have been recognized because they bear a numerous and diverse fauna of vertebrate fossils, particularly mammals. Among these, the members of the order Notoungulata represent one of the most conspicuous elements. Since the 19th century, different expeditions to the region have provided excellent notoungulate fossils. However, while the knowledge of the group in the Neogene of South America has increased in the last two decades, the specimens of NWA have been scarcely included in systematic, phylogenetic, biostratigraphic and paleobiogeographic studies. In this framework, the present thesis focuses on the members of three families of the order Notoungulata (Toxodontidae, Mesotheriidae, and Hegetotheriidae) from different Neogene outcrops of the region.Prospection in several NWA provinces (Jujuy, Salta, Tucumán, Catamarca and Santiago del Estero) allowed discovering a great number of specimens stratigraphically located and georeferenced. In this way, this study includes both new records and previously determined materials. The prospected outcrops belong to units grouped into two geological provinces: Sierras Pampeanas Noroccidentales (better-known outcrops with the greater fossil record) and Llanura Chaqueña, for which the first records of notoungulates are provided.Within the family Toxodontidae, remains referred to aff. "Andinotoxodon" are recognized. This taxon was informally established, and then, a synthesis of the taxonomical problem is here detailed. Additionally, a new species of the genus Xotodon (X. caravela) is identified for which a phylogenetic analysis is carried out, recovering a synapomorphy for the genus which lead to an amendment to its diagnosis. On the other hand, the first record of the genera Ocnerotherium and Pisanodon for the NWA is mentioned, increasing the diversity of the group in the region.Regarding Mesotheriidae, new useful traits are proposed to differentiate Typotheriopsis from Pseudotypotherium, which are important for the assignment of incomplete or non-associated remains. A detailed description of new materials corresponding to species of mentioned genera is made. In some materials, intermediate features between Argentinean and Bolivian taxa are recognized. Remains referred to Plesiotypotherium cf. P. achirense are mentioned, which represents the first record of the genus for Argentina. On the other hand, paleobiological analyzes related to the Mesotheriidae diet recognized four morphotypes associated with the selection of food. A strong correlation is observed between the evolutionary history of the Mesotheriidae and the mentioned morphotypes, which includes size, phylogenetic relationships and temporal distribution aspects of the different taxa.For the family Hegetotheriidae, new records of Hemihegetotherium achataleptum are documented. At the same time, there are materials referred to Hemihegetotherium cf. H. achataleptum and Hemihegetotherium sp. which show some particularities related to size. Regarding the subfamily Pachyrukhinae, Tremacyllus incipiens is revalidated as a species of the genus. In turn, previous hypotheses that establish an endemism of the species for the NOA are reconsidered. On the other hand, complete materials assigned to Paedotherium typicum and P. bonaerense are described, being the first record in the region.Based on the fossil record, largest notoungulates (i.e., toxodontids) show a differential distribution, with different populations on both sides of the main ranges (i.e., Cumbres Calchaquíes and Sierras del Aconquija). On the other hand, smaller groups (i.e., hegetotheriids) have a wider distribution, with common taxa for both sides of the ranges. So far, mesotheriids findings are focused in the western valley outcrops. In these areas, there are forms close to Bolivian and Chilean faunas. On the other hand, the mesotheriids are scarcely represented in the lowland areas of NWA. This latter may be due to a bias in the sampling, given the recent interest in the plain outcrops of the region.According to this study, it is confirmed that the notoungulate diversity of the Northwestern Argentina during the Miocene-Pliocene was considerably larger than previously established. In turn, for some groups (i.e., Hegetotheriidae and Toxodontidae) the inferred discrepancy regarding the faunal composition of the NWA in relation to the rest of Argentina is attributed to a bias in the fossil record.The fossil levels of the Neogene continental outcrops of Northwestern Argentina (NWA) are well-known by their great extension and represent a span from approximately 11 to 2.5 Ma (late Miocenelate Pliocene). Historically, these units have been recognized because they bear a numerous and diverse fauna of vertebrate fossils, particularly mammals. Among these, the members of the order Notoungulata represent one of the most conspicuous elements. Since the 19th century, different expeditions to the region have provided excellent notoungulate fossils. However, while the knowledge of the group in the Neogene of South America has increased in the last two decades, the specimens of NWA have been scarcely included in systematic, phylogenetic, biostratigraphic and paleobiogeographic studies. In this framework, the present thesis focuses on the members of three families of the order Notoungulata (Toxodontidae, Mesotheriidae, and Hegetotheriidae) from different Neogene outcrops of the region. Prospection in several NWA provinces (Jujuy, Salta, Tucumán, Catamarca and Santiago del Estero) allowed discovering a great number of specimens stratigraphically located and georeferenced. In this way, this study includes both new records and previously determined materials. The prospected outcrops belong to units grouped into two geological provinces: Sierras Pampeanas Noroccidentales (better-known outcrops with the greater fossil record) and Llanura Chaqueña, for which the first records of notoungulates are provided. Within the family Toxodontidae, remains referred to aff. "Andinotoxodon" are recognized. This taxon was informally established, and then, a synthesis of the taxonomical problem is here detailed. Additionally, a new species of the genus Xotodon (X. caravela) is identified for which a phylogenetic analysis is carried out, recovering a synapomorphy for the genus which lead to an amendment to its diagnosis. On the other hand, the first record of the genera Ocnerotherium and Pisanodon for the NWA is mentioned, increasing the diversity of the group in the region. Regarding Mesotheriidae, new useful traits are proposed to differentiate Typotheriopsis from Pseudotypotherium, which are important for the assignment of incomplete or non-associated remains. A detailed description of new materials corresponding to species of mentioned genera is made. In some materials, intermediate features between Argentinean and Bolivian taxa are recognized. Remains referred to Plesiotypotherium cf. P. achirense are mentioned, which represents the first record of the genus for Argentina. On the other hand, paleobiological analyzes related to the Mesotheriidae diet recognized four morphotypes associated with the selection of food. A strong correlation is observed between the evolutionary history of the Mesotheriidae and the mentioned morphotypes, which includes size, phylogenetic relationships and temporal distribution aspects of the different taxa. For the family Hegetotheriidae, new records of Hemihegetotherium achataleptum are documented. At the same time, there are materials referred to Hemihegetotherium cf. H. achataleptum and Hemihegetotherium sp. which show some particularities related to size. Regarding the subfamily Pachyrukhinae, Tremacyllus incipiens is revalidated as a species of the genus. In turn, previous hypotheses that establish an endemism of the species for the NOA are reconsidered. On the other hand, complete materials assigned to Paedotherium typicum and P. bonaerense are described, being the first record in the region. Based on the fossil record, largest notoungulates (i.e., toxodontids) show a differential distribution, with different populations on both sides of the main ranges (i.e., Cumbres Calchaquíes and Sierras del Aconquija). On the other hand, smaller groups (i.e., hegetotheriids) have a wider distribution, with common taxa for both sides of the ranges. So far, mesotheriids findings are focused in the western valley outcrops. In these areas, there are forms close to Bolivian and Chilean faunas. On the other hand, the mesotheriids are scarcely represented in the lowland areas of NWA. This latter may be due to a bias in the sampling, given the recent interest in the plain outcrops of the region. According to this study, it is confirmed that the notoungulate diversity of the Northwestern Argentina during the Miocene-Pliocene was considerably larger than previously established. In turn, for some groups (i.e., Hegetotheriidae and Toxodontidae) the inferred discrepancy regarding the faunal composition of the NWA in relation to the rest of Argentina is attributed to a bias in the fossil record.Fil: Armella, Matías Alberto. 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; Argentin

Biostratigraphic significance of the presence of Protypotherium cf. P. antiquum Ameghino 1885 (Interatheriidae, Notoungulata) in the late Miocene of Northwestern Argentina

Interatheriinae (Notoungulata, Interatheriidae) includes small, rodent-like, and cursorial mammal herbivores. They are known from the early Oligocene and became abundant during the early to middle Miocene in several South American localities. Throughout the late Miocene, interatheriines were only reported by a few remains from Argentinean outcrops. Here, we present a new finding from the Chiquimil Formation, Catamarca Province (Argentina). The specimen is assigned to Protypotherium cf. P. antiquum based on the large size, high teeth imbrication, and absence of a sulcus in the lingual surface of the trigonid and talonid of p4, in comparison to late representatives of Interatheriinae. The chronostratigraphic context allows us to consider last intheratheriine records as a Last Appearance Datum (LAD), important to establish biostratigraphic and/or chronostratigraphic units in the late Miocene. The scarce interatheriine records and paleoenvironmental approaches during this lapse suggest that the C3/C4 biomass change and the radiation of the Hegetotheriidae lineage probably affected the already reduced population of interatheriines and led to their final disappearance.Fil: Armella, Matías Alberto. Instituto de Estratigrafia y Geologia Sedimentaria Glob; Argentina. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. 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; ArgentinaFil: Bonini, R.A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Investigaciones Arqueológicas y Paleontológicas del Cuaternario Pampeano. Universidad Nacional del Centro de la Provincia de Buenos Aires. Investigaciones Arqueológicas y Paleontológicas del Cuaternario Pampeano; Argentin

What else is dentition telling us? A new specimen‐level phylogeny of Mesotheriidae (Mammalia, Notoungulata)

Mesotheriidae (Panperissodactyla, Notoungulata) is an extinct clade (early Oligocene–Pleistocene) of small to medium-sized herbivorous mammals that were widely distributed in South America. Although two subfamilies have been traditionally recognized (Trachytheriinae and Mesotheriinae), recent cladistic analyses based on discrete characters have indicated that “Trachytheriinae” is a paraphyletic assemblage. Given the availability of a large number of specimens and the fact that dental characters are the most common characters used in mesotheriid phylogenies, we performed specimen-level cladistic analyses combining discrete, continuous, and geometric morphometrics-based dental characters. The aim was to: (1) include new scored morphological characters to solve the phylogenetic relationships of Mesotheriidae; (2) compare the results of the upper and lower dentition analyses as different character partitions and in combination, to establish phylogenetic hypotheses; (3) trace the evolution of dental traits. Phylogenetic analyses employing characters of associated upper and lower dentitions recovered one most parsimonious tree with Archaeohyracidae (outgroup) as the sister group of Pan-Mesotheriidae (= Mesotheriidae; converted clade name), this latter composed of trachytheriines (stem-mesotheriine) + Mesotheriinae (converted clade name). Within Mesotheriinae, we recovered two main lineages phylogenetically defined here as Bolivarini and Pampaini (new clade names). Analyses of isolated upper and lower dentition sub-datasets each resulted in one most parsimonious tree congruent with the associated dentition. Our study emphasizes the use of geometric morphometrics characters to resolve additional clades in phylogenetic analyses, provides information on the evolution of size and morphology of teeth, and exposes specimen assignment issues at a taxonomic level. The integration of osteological characters might be crucial to further understanding the evolution of Mesotheriidae.Fil: Armella, Matías Alberto. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. 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 Catamarca. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Deforel, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentin

An Evaluation of the Dental Features Used to Distinguish Typotheriopsis from Pseudotypotherium (Mesotheriidae, Notoungulata): Reappraisals and Proposals Regarding Their Systematic Value

The marginal-marine, low-energy, carbonate ramp deposits of the La Tosca Member (Huitrín Formation, Barremian) in southern Mendoza Province, Argentina, bear an abundant though low-diversity macrobenthic invertebrate fauna that is scarce or absent in the outcrops of the unit in the Neuquén Province. Here we describe new taxa from the Quebrada del Gastrópodo and Ranquil 1 sections and provide taxonomic revisions for other key faunal elements. The species discussed herein are the gastropods Paleoanculosa macrochilinoides (Doello-Jurado), Provalvata minor sp. nov., and Provalvata maior sp. nov., the bivalve Rutitrigonia cintarojensis sp. nov., and the serpulid Parsimonia aff. laevis (Goldfu?). Additionally, in order to analyze the observed changes in faunal content along the studied section, a paleoecological analysis was performed combining estimation of diversity indices and the paleoautoecology of the fauna recorded in Quebrada del Gastrópodo. Three macrobenthic assemblages were qualitatively recognized in the field; from base to top: 1) Paleoanculosa macrochilinoides, 2) serpulid-gastropod, and 3) bivalve-serpulid assemblages. Species richness and equitability increase upwards. This trend suggests a reduction in environmental stress from bottom to top. The first two assemblages indicate settings with fluctuating environmental parameters, whilst the third points to higher environmental stability. Euryhaline taxa dominate, whilst stenohaline species are scarce or absent in the lower two thirds of the succession. The nature of the stress is interpreted herein to be mainly related to high-frequency salinity variations, especially in the first and second assemblages in which temporal deviations from euhaline to meso-brachyhaline and brachyhaline conditions are hypothesized.Fil: Armella, Matías Alberto. 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; ArgentinaFil: Ercoli, Marcos Darío. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentin

Los tesoros ocultos en Termas de Río Hondo (Santiago del Estero)

Termas de Río Hondo es una ciudad del noroeste argentino (NOA) localizada en la provincia de Santiago del Estero. Este lugar es reconocido como uno de los principales destinos turístico de la región (presencia de aguas termales y por la organización de eventos deportivos). Sin embargo, en los alrededores de la ciudad de las Termas se encuentra oculto uno de los legados más importantes de la naturaleza. A continuación, se brinda un panorama integral de los restos fósiles encontrados en las Termas de Río Hondo, haciendo referencia a los lapsos temporales representados en los afloramientos.Fil: Armella, Matías Alberto. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. 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; ArgentinaFil: Esteban, Graciela Irene. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. 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; ArgentinaFil: Sabater, Sebastian. Museo Municipal Rincón de Atacama; Argentin

Small-sized mesotheriines (Mesotheriidae, Notoungulata) from Northwestern Argentina: Systematic, chronological, and paleobiogeographic implications

The Neogene outcrops in Northwestern Argentina have provided many fossil mammals, particularly notoungulates. However, the fossil record of the early stages of the late Miocene is scarce. The present study describes two mesotheriine specimens from Las Arcas Formation (underlying the Chiquimil Formation dated at 9.14 ± 0.09 Ma; Catamarca Province) and Saladillo Formation (dated at 10 ± 0.3 Ma; Tucumán Province), represented by a left maxillary fragment with complete M1–3 and a right isolated M3, respectively. The main feature of these pieces is their small size, significantly smaller than that of the Miocene genera Eutypotherium, Typotheriopsis, and Pseudotypotherium, recorded in Argentina. In contrast, these mesotheriines are closer to specimens known from Bolivia. The comparative analysis allows us to refer the material herein described to Plesiotypotherium aff. P. achirense and Mesotheriinae indet., with all cautions inherent to the incompleteness of the material. In turn, the paleobiogeographic implication of these new records is approached. A relationship concerning phylogenetic aspects, size, temporal range, and distribution pattern is proposed, taking into account the small size of the studied material in a temporal context of medium to large-sized mesotheriines.Fil: Armella, Matías Alberto. 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; ArgentinaFil: Nasif, Norma. 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; ArgentinaFil: Cerdeño Serrano, Maria Esperanza. 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; Argentin

A new species of Xotodon (Notoungulata, Toxodontidae) from northwestern Argentina

Xotodon caravela, a new species of toxodontid from northwestern Argentina, is presented. The material studied consists of a well-preserved and nearly complete mandible and a maxillary fragment, recovered in the Aconquija Formation (late Miocene-early Pliocene) at the El Molino locality (Tucumán Province, Argentina). The fossil diversity of the levels is concordant with an early Pliocene fauna. The general features of the dentition and mandible (e.g., concave ectoloph and single lingual fold on upper molars, anterior fold mesially displaced relative to the hypoflexid in the lower molars, sigmoid lateral outline of chin, and continuous enamel on M3) allow the inclusion of this specimen in the genus Xotodon. In turn, some traits indicate unequivocally that this is a new species, such as the anterior region without constriction at the premolar level, the approximately 13° angle of implantation of the i3 in relation to the ventral edge of the mandibular body (without lateral divergence), and the presence of an intra-alveolar projection of the incisive crown extending laterally below the premolars to the level of the p4 and forming a robust projection or lateral ledge. The new taxon was included in a matrix of 59 characters and compared with 32 notoungulate genera. The phylogenetic position and comparative analysis support the taxonomic interpretation of the studied specimen as a new species of Xotodon. This represents the first record of a toxodontid in the Neogene lowlands of northwestern Argentina and contributes to our knowledge of this family in the region.Fil: Armella, Matías Alberto. 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; ArgentinaFil: 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; ArgentinaFil: Domínguez, Lucía Inés. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentin