an ancient lineage of mammals comprising the armadillos (order Cingulata) and the sloths and anteaters (order Pilosa). The namesake feature shared by all members of Xenarthra is seen in the lower backbone. The lumbar vertebrae are "xenarthrous"; that is, they have extra contacts (joints, or arthroses) that function to strengthen the lower back and hips. This aids use of the forelegs in activities not associated with locomotion, such as digging-the primary method used by anteaters and armadillos to obtain food.
Learn more about xenarthran with a free trial on Britannica.com.