ANALYSIS OF DENTAL MICROWEAR IN TREE SLOTHS AND ARMADILLOS: DOES SCANNING ELECTRON MICROSCOPY REVEAL A LINK BETWEEN DIET AND TOOTH SCARRING?

Dental microwear has recently been identified as a proxy for feeding ecology in xenarthrans. Understanding the correlation between microwear patterns and diet in tree sloths and armadillos will provide baseline data that can be used to test hypotheses of paleoecology in extinct ground sloths and glyptodonts. However, the causal relationship between diet and fine-scale tooth wear in this clade has been studied almost exclusively using low-magnification light microscopy. Here, we use high-magnification scanning electron microscopy (SEM) to statistically test the hypothesis that microwear patterns are significantly different among tree sloths and armadillos. Microwear patterns on 26 teeth from five xenarthran species were analyzed; each species was classified into one of four dietary groups: 1. carnivore-omnivores = Euphractus sexcinctus; 2. folivores = Bradypus variegatus; 3. frugivore-folivores = Choloepus didactylus, C. hoffmanni; 4. insectivores = Dasypus novemcinctus. Using SEM, two non-overlapping digital images of microwear on the occlusal surface of each tooth were captured at 500X magnification. In a blind study, microwear features on each image were digitally counted and measured by 2 independent observers. This allowed us to test for and help control observer error in microwear feature recognition. Pearson correlation coefficients reveal that both observers’ data sets were highly correlated (i.e., both observers were able to independently distinguish the same relative scar patterns among xenarthran dietary groups). Insectivores and folivores consistently had the lowest number of scratches and greatest width of scar features relative to frugivore-folivores and carnivore-omnivores. However, only one observer produced mean microwear variables that were significantly different among dietary groups. This inconsistent result may stem from error in identifying scar features on dentine, which has a more complex, rugged surface compared to enamel. As a next step, this method should be applied to ground sloths and glyptodonts to further test its ability to distinguish potential dietary differences among these taxa.