Fil: Fernández, Marta S. Universidad Nacional de La Plata. Museo de La Plata. División Paleontología de Vertebrados. Buenos Aires, Argentina.Fil: Herrera, Yanina. Universidad Nacional de La Plata. Museo de La Plata. División Paleontología de Vertebrados. Buenos Aires, Argentina.Fil: Vennari, Verónica V. Museo de Historia Natural de San Rafael. Grupo vinculado al Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Mendoza, Argentina.Fil: Campos, Lisandro. Universidad Nacional de La Plata. Museo de La Plata. División Paleontología de Vertebrados. Buenos Aires, Argentina.Fil: De La Fuente, Marcelo. Museo de Historia Natural de San Rafael. Grupo vinculado al Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Mendoza, Argentina.Fil: Talevi, Marianella. Universidad Nacional de Río Negro. Instituto de Investigación en Paleobiología y Geología. Río Negro, Argentina.Fil: Aguirre Urreta, Beatriz. Univesidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. Instituto de Estudios Andinos “Don Pablo Groeber". Buenos Aires, Argentina.Fil: Vennari, Verónica V. Consejo Nacional de Investigaciones Científicas y Técnicas. Mendoza, Argentina.Fil: De La Fuente, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Mendoza, Argentina.Fil: Talevi, Marianella. Consejo Nacional de Investigaciones Científicas y Técnicas. Río Negro, Argentina.Fil: Aguirre Urreta, Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Buenos Aires, Argentina.Upper Jurassic and Lower Cretaceous deposits of the Vaca Muerta Formation (Neuquén Basin, central-west Argentina) have yielded abundant marine reptile remains. Most of them correspond to faunal assemblages recovered from outcrops in the Neuquén Province (Argentina). Herein we report two new marine reptile-bearing localities documenting the Tithonian–Berriasian transition at the High Andes (Mendoza Province, Argentina). Marine reptiles have been mapped and/or collected in connection with an accurate ammonoid-based biostratigraphic control. All the skeletons have been found preserved in, or associated with, calcareous nodules. At both localities they are frequent in beds assigned to the upper Tithonian ammonite Zone (Microcanthum to “Durangites” Standard Zones), and are rare to common in beds assigned to the upper Tithonian–lower Berriasian Substeueroceras koeneni Zone (“Durangites” to Jacobi Standard Zones). Newly discovered assemblages depict a similar pattern characterized by the lack of plesiosaurs (plesiosauroids and pliosaurids), and by the abundance of mesoconsumers represented by ophthalmosaurids and metriorhynchine metriorhynchids. Macropredator geosaurines, apex metriorhynchids predators, and thalassochelydian turtles are rare components of these assemblages.trueUpper Jurassic and Lower Cretaceous deposits of the Vaca Muerta Formation (Neuquén Basin, central-west Argentina) have yielded abundant marine reptile remains. Most of them correspond to faunal assemblages recovered from outcrops in the Neuquén Province (Argentina). Herein we report two new marine reptile-bearing localities documenting the Tithonian–Berriasian transition at the High Andes (Mendoza Province, Argentina). Marine reptiles have been mapped and/or collected in connection with an accurate ammonoid-based biostratigraphic control. All the skeletons have been found preserved in, or associated with, calcareous nodules. At both localities they are frequent in beds assigned to the upper Tithonian ammonite Zone (Microcanthum to “Durangites” Standard Zones), and are rare to common in beds assigned to the upper Tithonian–lower Berriasian Substeueroceras koeneni Zone (“Durangites” to Jacobi Standard Zones). Newly discovered assemblages depict a similar pattern characterized by the lack of plesiosaurs (plesiosauroids and pliosaurids), and by the abundance of mesoconsumers represented by ophthalmosaurids and metriorhynchine metriorhynchids. Macropredator geosaurines, apex metriorhynchids predators, and thalassochelydian turtles are rare components of these assemblages.