CONICET | Buscador de Institutos y Recursos Humanos

This contribution summarizes the fossil vertebrates recovered at the Eocene of northwestern Argentina during the last 30 years, including the record of the Lumbrera, Geste, Quebrada de los Colorados, and Casa Grande Formations. Field work and several publications and doctoral theses carried out by researchers from the Museo de La Plata, Instituto Miguel Lillo (Tucumán), and Museo Municipal de Mar del Plata improved the knowledge of the diversity, evolutionary history, and chronology of this fossil fauna. Sedimentological, structural, and stratigraphic studies recently conducted by geologists from Universidad de Salta and Universidad de Tucumán provided information related to lithology, paleoenvironment, and age of these Eocene deposits, along with evidence of the correlation among northwestern and Patagonian stratigraphic units. The Eocene formations of northwestern Argentina show high taxonomic diversity. The fossil fauna includes several groups of vertebrates: lungfishes, cichlid fishes, crocodiles, turtles, lizards, snakes, and, among mammals, metatherians, xenarthrans, and ungulates (astrapotherians, litopterns and notoungulates). Most of the mammalian groups are represented by endemic genera, and some families present their oldest records in these units. Traditionally, the Lumbrera Formation was considered lower Eocene in age, while Geste and Casa Grande Formations were considered younger (middle to upper Eocene). Recently, geologic and paleontologic evidence allowed the correlation of the upper levels of Lumbrera with Geste, Casa Grande, and Quebrada de los Colorados Formations. Additionally, these levels were referred to the late-middle Eocene (Casamayoran SALMA -South American Land Mammal Age-, Barrancan subage) by an U/Pb dating of 39.9 Ma . The lower levels of the Lumbrera Formation are here referred to the Vacan subage of the Casamayoran SALMA. Keywords: Paleogene - northwestern Argentina - vertebrates - biostratigraphy - anatomy