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

Abstract

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.