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Hegetotheriidae is one of the most derived families of South American notoungulates, which are known from the late Oligocene to Pliocene. Several genera of hegetotheriids have been described; most of them have been recently re-examined, but the Miocene taxa Hegetotherium and Pachyrukhos have not been revised for more than a century. Numerous species of both genera were described mainly from the Santa Cruz Formation, Santa Cruz Province, but also from the Colhuehuapian beds in Chubut Province, and the Colloncuran beds in Neuquén and Río Negro provinces, Argentina. Recently, Hegetotherium was recorded in Bolivia and Chile. Sinclair was the first reviewer to postulate some synonymies, in the first decade of the twentieth century. The present contribution provides a re-evaluation of these genera, including the study of previously unpublished materials. We conclude that Hegetotherium mirabile and Pachyrukhos moyani are the only hegetotheres in the Santa Cruz Formation (Santacrucian SALMA) with Hegetotherium novum and Pachyrukhos politus in the Colhuehuapian SALMA. Additionally, H. convexum, H. anceps, H. minum and H. andinum are proposed as synonyms of H. mirabile; H. novum is removed from Prohegetotherium; and Hegetotherium arctum is excluded from Hegetotheriidae. This taxonomic revision led to a new phylogenetic analysis of Hegetotheriidae, based on a previous data matrix, but enlarged and corrected, as some taxonomic issues concerning other genera were revealed. The analysis supports the monophyly of Hegetotheriidae and the subfamily Pachyrukhinae, as well as the monophyly of the genera Hemihegetotherium and Paedotherium, if the proposed removal of Pd. kakai from the latter is admitted. In contrast, Hegetotheriinae and Hegetotherium appear to be paraphyletic. The position of H. novum supports its removal from the genus Prohegetotherium, in which it was recently included. Fil: Seoane, Federico Damián. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geologicas. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; 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

Two genera of the subfamily Pachyrukhinae (Notoungulata, Hegetotheriidae), Paedotherium and Tremacyllus, are revised. The material comes from late Miocene (Chasicoan) to early Pleistocene (Marplatan) localities in Argentina and Bolivia. The genus Raulringueletia is here considered a synonym of Paedotherium. Three valid species of Paedotherium are recognized and re-characterized: P. bonaerense, P. typicum, and P. minor. Two species of Tremacyllus are recognized: T. impressus in the Pampean region, and T. incipiens in Catamarca Province. The presence of Tremacyllus sp. into the late Chasicoan extends its known temporal range. Pachyrukhos occurs slightly earlier within the Chasicoan, coexisting with Paedotherium. Paedotherium is dominant in frequency in the Pampean area (Buenos Aires and La Pampa) and extremely scarce in the Subandean region (Catamarca), while Tremacyllus has an opposite occurrence. Cladistic analysis of the subfamily shows Paedotherium as a monophyletic group, where P. bonaerense i...

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