The living tree sloths Choloepus and Bradypus are the only remaining members of Folivora, a major xenarthran radiation that occupied a wide range of habitats in many parts of the western hemisphere during the Cenozoic, including both continents and the West Indies (Antilles). To date, molecular evidence has played only a minor role in folivoran systematics, as most recently-extinct species lived in places not conducive to DNA preservation. Here we utilize collagen sequence information to assess the relationships of tree sloths to a large sample (13 species) of extinct Quaternary folivorans.