| Abstract |
Understanding the paleoecology of extinct xenarthrans, such as ground sloths, is complicated because they lack living 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 are statistically different among extinct ground sloths, thereby providing new evidence of feeding ecology in these animals. In a blind study, the dental microwear patterns in three extinct taxa representing two clades [Megalonyx wheatleyi and Acratocnus odontrigonus in Megalonychidae, Thinobadistes segnis in Mylodontidae] were quantitatively analyzed using scanning electron microscopy at 5003 magnification. Two independent observers recovered similar relative trends in microwear patterns between M. wheatleyi, A. odontrigonus, and T. segnis, with mean number of scratches and feature width being the most informative variables among taxa. Microwear patterns in M. wheatleyi correspond most closely with living selective xenarthran herbivores (i.e., Bradypus), with a low number of scratches but a high feature width. T. segnis, in contrast, has an unusually high number of scratches but low feature width, which is unlike any patterns exhibited by living xenarthrans and indicates possible grazing habits. A. odontrigonus falls between these two extremes, which we interpret as a more generalized browser, similar to Choloepus. Microwear patterns among living and extinct sloths sampled to date seem to fall along a continuum of herbivorous feeding strategies, with grazing and selective browsing representing the two extremes. Although we only examine three taxa, our results (stemming from a blind analysis that accounts for observer error) support the feasibility of using high-magnification dental microwear to examine feeding ecology in extinct ground sloths.
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