AMOUNT OF OCCLUSAL ENAMEL IN UNGULATES CORRELATES WITH BODY MASS

Determining diet in ancient mammals is important for understanding paleoecological processes such as resource partitioning and competition. Many morphological characters have been shown to correlate with the diet of herbivorous mammals, including such proxies as tooth crown height and shape of the premaxilla. Studies have shown that enamel microstructure and orientation of enamel bands are functionally related to tooth stresses during feeding. Animals with different diets and stresses on the occlusal surface have different enamel band orientations. For some herbivores, especially within the Equidae, the occlusal enamel pattern appears to become more complex over time with addition of structures such as plications on the fossettes. This study attempted to determine how this increase in occlusal enamel complexity, as measured using the length of the cutting surface of the enamel, correlates with diet. Maxillary cheek teeth of 163 individuals from 63 ancient and modern ungulate taxa were digitally imaged and measured. Results indicate that occlusal enamel length is significantly correlated to body mass, using both a simple linear regression and in a phylogenetic analysis using independent contrasts. However, there was no correlation between the enamel length and diet. Perissodactyls have a larger enamel length per body mass compared to artiodactyls. The ancient horses Hipparion forcei, Neohipparion eurystyle, and Neohipparion leptode appear to have largest enamel lengths, which may indicate an influence on the enamel length and pattern other than body mass. These results suggest that the pattern of the occlusal enamel in ungulate teeth is primarily determined by the mass of the individual, not the diet.