Dental evolution in Neophanomys (Rodentia, Octodontidae) from the late Miocene of central Argentina

Abstract

The evolutionary pattern of the molar morphology of the small caviomorph (Octodontidae) Neophanomys from the late Miocene Cerro Azul Formation of central Argentina is analyzed. Two new species (chronomorphs) are recognized, which constitute an anagenetically evolving lineage with a gradual and directional pattern of increasing molar hypsodonty. Dental changes related to increasing hypsodonty are comparable to those of the octodontid lineage Chasichimys also recovered from the Cerro Azul Formation. However, Neophanomys shows comparatively less variation in gross morphology and there are no evidences that this lineage achieved euhypsodonty. In contrast, important changes in enamel microstructure (schmelzmuster) are observed among different populations of Neophanomys, supporting the hypothesis that these changes can occur at least partially independently from modifications in dental gross morphology. The patterns of dental evolution detected in the Neophanomys and Chasichimys- Xenodontomys lineages and the unequivocal polarity of the changes involved, related to increasing hypsodonty, reinforce the hypothesis that chronological differences exist among late Miocene outcroppings of Cerro Azul Formation in central Argentina.