Stratigraphic provenance and age of the oldest muroids (Mammalia, Rodentia) in South America

The exact stratigraphic provenance of Auliscomys formosus Reig and Necromys bonapartei (Reig), the oldest muroids in South America, has been debated d uring several years. The stratigraphic data given by Reig were not enough t o establish the exact stratigraphic location in the type area, that is, the Farola Monte Hermoso marine cliffs, southern Buenos Aires Province, Argent ina. However, examination of the original labels attached to the material a t the Instituto Miguel Lillo, revealed that the holotype of A. formosus cam e from the "Banco N degrees 3" (sensu Bonaparte), the lower part of the Mon te Hermoso Formation (sensu Zavala), Biozone of Trigodon gaudryi (sensu Clo ne and Tonni), Montehermosan Stage, Early Pliocene. By contrast, the holoty pe of N. bonapartei was found in the "Miembro de limolitas claras", upper p art of Monte Hermoso Formation, Biozone of Neocavia depressidens, lower Cha padmalalan Stage, Early Pliocene. The holotype of A. farmosus is the only m uroid specimen occurring in rocks older than Chapadmalalan.