PROCEDENCIA ESTRATIGRÁFICA y EDAD DE LOS MÁS ANTIGUOS MUROIDEOS (MAMMALIA, RODENTIA) DE AMÉRICA DEL SUR

Abstract

The exact stratigraphic provenance of Auliscomys formosus Reig and Necromys bonapartei (Reig), the oldest muroids in South America, has been debated during several years. The stratigraphic data given by Reig were not enough to establish the exact stratigraphic location in the type area, thar is, the Farola Monte Hermoso marine cliffs, southern Buenos Aires Province, Argentina. However, examination of the original labels attached to the material at the Instituto Miguel Lillo, revealed that theholotype of A. formosus carne from the "Banco N° 3" (sensu Bonaparte), the lower part of the Monte Hermoso Formation (sensu Zavala), Biozone of Trigodon gaudryi (sensu Cione and Tonni), Montehermosan Stage, Early Pliocene. By contrast, the holotype of N. bonapartei was found in the "Miembro de limolitas claras", upper part of Monte Hermoso Formation, Biozone of Neocavia depressidens, lower Chapadmalalan Stage, Early Pliocene. The holotype of A. formosus is the only muroid specimen occurring in rocks older than Chapadmalalan.