Like most mammals, we humans have a variety of tooth types for different purposes: incisors, for gripping, canines for ripping and tearing, and molars (also pre-molars) for grinding and chewing. But one group, known as the Xenarthra (a particularly excellent name meaning “strange joints”), have very simple dentition, with similar, unrooted teeth which lack enamel and grow continually from birth. This group includes anteaters, armadillos and sloths. Sloths actually have a very conserved tooth pattern, with five upper and four lower teeth. However, there is debate about the classification of the canines, it’s very tricky to distinguish between the molars and pre-molars and there were thought to be no incisors at all. Now, researchers have bridged the apparent gap between sloths and other mammals and identified the different tooth types in two- and three-toed species. By CT-scanning a series of animals through their development from foetuses to adults, Lionel Hautier and colleagues were able to pick out similarities and differences between individual teeth in different animals and stages of development. They even found vestigial incisors in the three-toed sloth Bradypus (below), which had never been identified before. The team hope that the new wealth of data on the two sloth groups will help them to form a clearer picture of tooth pattern in ancestral sloths and crack the mystery of how sloths evolved this peculiar arrangement.

Image courtesy of Lionel Hautier. For the full article, click here.