USING SCANNING ELECTRON MICROSCOPY TO RECONSTRUCT FEEDING ECOLOGY IN GROUND SLOTHS

Understanding the paleoecology of extinct xenarthrans, such as ground sloths, is complicated because they lack modern ecological analogues. Previous studies have applied functional morphology and biomechanical analyses to reconstruct the diet and lifestyle of ground sloths, yet the application of dental microwear as a proxy for feeding ecology in extinct xenarthrans remains understudied. Here, we hypothesize that dental microwear patterns can be used to reconstruct dietary niche partitioning among extinct ground sloths, thereby providing new evidence of feeding ecology in these animals.

In this study, 20 second molariforms from 6 taxa [Megalonyx, Acratoncus, Thinobadistes, Octodontotherium, Hapalops, Scelidotherium] were molded and cast for dental microwear analysis. Using scanning electron microscopy, two non-overlapping digital images of microwear on the occlusal surface of each tooth were captured at 500x magnification. In a blind study, each image was independently analyzed using the semi-automated software package, Microwear 4.02, which allows microwear features to be digitally counted and measured. To examine the reproducibility of results, both intra- and inter-observer error in microwear feature recognition was statistically assessed for 2 independent observers. As a baseline for reconstructing paleodiet, ground sloth microwear patterns were directly compared to microwear from living tree sloths and armadillos, which were analyzed separately using the same experimental design. Results suggest that ground sloths are differentiated based on a combination of quantitative features, including number of scratches, number of pits, feature width, and relative orientation of scars.