Armadillos, sloths, and anteaters (Xenarthra) are notable for the unique joints in their backbone that provide them with the strength and support they need to dig and burrow. Armadillos, sloths, and anteaters have few or no teeth and a small brain.
Xenarthra are an ancient group of placental mammals that once roamed across Gondwanaland before the continents of the southern hemisphere separated into their present-day configuration. When Gondwanaland divided, it split up to form South America, Africa, India, Arabia, New Zealand, and Australia. Xenarthra were initially isolated on the continent of South America but have since spread northward into areas of Central America and southern parts of North America.
Though xenarthran populations were absent from Africa, Asia, and Australia, these regions contain unrelated species that evolved to resemble xenarthrans. Similar environmental conditions in these distant parts of the world resulted in species that, although unrelated, adapted in a similar manner and as a result resemble each other in some ways. This evolutionary dynamic is known as convergent evolution.
Examples of species that display convergent evolution with the xenarthrans include the aardvark (Africa), the pangolin (Africa and SE Asia), and the spiny anteater (Australia). These animals all have genetically different ancestors than the xenarthrans and consequently belong to different orders than the xenartrhans, yet they have evolved similar characteristics.