CONICET | Buscador de Institutos y Recursos Humanos

Old and new specimens from the early Miocene middlemember of the Mariño Formation (Mendoza, Argentina) allow for areinterpretation of a controversial Mesotheriidae taxon. Earlier known remainscome from the Divisadero Largo locality and were, depending on the specimen,either previously described as Trachytherus? mendocensis or referred toa coeval taxon from Chile, Altitypotherium chucalensis. Based on newspecimens, here described in detail for the first time, we propose that allmesotheriid material from Divisadero Largo, as well as new material from thePotrerillos locality belong to a new mesotheriid taxon. Recognition of the sametaxon from these two localities establishes a sound biostratigraphiccorrelation. The combination of morphological characters leads to the proposalof a new generic name, Rusconitherium, for ?Trachytherus? mendocensis,establishing Rusconitherium mendocense New genus and New Combination.This nomenclatural act is due to the fact that T.? mendocensis, formerlythought as a Trachytheriinae from the Paleogene Divisadero Largo Formation,actually comes from the Mariño Formation and belongs to the same taxon as the newmaterial. The missing holotype of T.? mendocensis prompts us to proposea neotype and a new diagnosis for this species, which better characterize theSantacrucian mesotheriids from Mendoza. A phylogenetic analysis does notsupport a close relationship between this species and Altitypotherium(or any other mesotheriine genus) counter to a previous hypothesis. An unnamednew taxon from the Chinches Formation (San Juan Province) could belong to Rusconitherium,but its full description is pending, as well as a thorough revision of mostMesotheriinae members. Sediments at Potrerillos reveal two paleoenvironmentalscenarios: dune fields, influenced by volcanic events, and capillary water thatprovided humid conditions encouraging vegetation and fauna.