Living and recently extinct edentates are easily distinguished from all other mammals by additional articulations between the lumbar vertebrae, which are termed xenarthrales. Thus, the suborder Xenarthra was named from. These bony extrusions provide lumbar reinforcement for digging. Living edentates differ from most mammals in having simple skulls with no canines, incisors, or premolar. They also have a double posterior vena cava vein.
Males have internal testes and a small penis with no glands.
The extinct edentates, which were much more diverse than the living edentates, are believed to have been mostly unspecialized herbivores. They were probably outcompeted by newer, more adaptive, invading species. The success of modern edentates was due to occupation of relatively narrow niches. New invaders were not in direct competition. Edentates move slowly over small home ranges.