Relationships and evolutionary significance of Neophanomys biplicatus (Rodentia, Octodontidae) from the late Miocene-early Pliocene of Argentina.

New materials of the octodontid rodent Neophanomys biplicatus Rovereto were recovered from sediments of the Cerro Azul Formation in La Pampa Province. They suggest a Late Huayquerian age for the fossiliferous beds. Analysis o f the molar ontogeny in this species shows a greater morphological diversit y than previously recognized. The holotype of "Eumysops" parvidens' Roveret o (originally referred to the Echimyidae) is a young individual of this spe cies. Neophanomys biplicatus is related to the extant species Octodontomys gliroides Gervais and d'Orbigny and to the Miocene lineage that includes Ch asichimys Pascual. These primitive octodontids may have been members of a b asal radiation from which the subfamily Ctenomyinae differentiated.