Xenarthran teeth are rootless and continuously growing. They lack an outer enamel layer and consist instead of a combination of 2 generally different varieties of dentine with or without an outer collar of cementum. This dental make-up is unique among mammals. In the last decade, xenarthran teeth have been subject to a number of studies regarding microscopic features, including analyses of microstructure and microwear patterns. Here, we present a review of the present knowledge in these 2 fields together with new results on feeding adaptations in the giant ground sloth, Megatherium americanum. Microwear patterns suggest that M. americanum fed mainly on plants with low to moderate intrinsic toughness, although we observe a trend that microwear patterns in extinct sloths may reflect habitat (i.e., feeding in open habitats with higher amounts of grit versus closed habitats with lower amounts of grit) as much as, if not more than, the texture of ingested food.