Enamel Structure of Cuvieronius hyodon (Proboscidea, Gomphotheriidae) with a Discussion on Enamel Evolution in Elephantoids

Dental material of the South American elephantoid Cuvieronius hyodon from the Late Pleistocene of the Tarija Basin, Bolivia was sampled for a comprehensive analysis of the microstructure of the enamel. To examine variability at the dentition level, enamel samples of the upper incisor, second deciduous premolar, and molars were sectioned. The incisor and cheek teeth enamel is compared to that of other proboscideans in order to reveal pbylogenetically and functional informative features useful to reconstruct the evolution of elephantoid enamel. Studies of the adaptations and evolution of proboscidean enamel have focused so far on molars. Nevertheless, given the possibility of an independent evolution of the enamel at different tooth positions, the variation of the enamel throughout the dentition needs to be taken into consideration when using enamel microstructural characters to infer proboscidean diversity and phylogeny. The results obtained from this study demonstrate the generality, among elephantoids, of the basic microstructural features of Cuvieronius hyodon enamel, allowing the characterization of the Elepbantoid Enamel (EE). The differentiation between incisor and molar enamel seen in elephantoids is shown to represent a primitive elephantiform trait, as it also occurs in Phiomia. The three-layered enamel of the cheek teeth appears as the sole synapomorphy of the Elephantoidea, though the character might be homoplastic within the Proboscidea. Characters of the prisms cross-section might be used, on the other hand, to define less inclusive clades within the Elephantoidea.