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, 17 second molariforms from 5 taxa [Megalonyx, Acratocnus, Thinobadistes, Octodontotherium, Hapalops] 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. 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 can be statistically differentiated based on a combination of the number of scratches and width of features. Number of scratches and feature width suggest that Megalonyx and Thinobadistes form the ends of the browser-grazer spectrum, respectively. Additionally, Acratocnus and Octodontotherium are here predicted to be mixed feeders, while Hapalops appears to be a grazer. These results support scanning electron microscopic analysis of dental microwear as a tool for reconstructing paleodiet in ground sloths. Further investigation should be into South American ground sloths to allow direct comparison with other methods of dietary reconstruction.