Glyptodon is part of the superorder of placental mammals known as Xenarthra. This clade of mammals also includes anteaters, tree sloths, armadillos, and extinct ground sloths and pampatheres.
Glyptodon originated in South America. During the Great American Interchange, a set of migrations that occurred after North and South America were connected by the rising of the volcanic Isthmus of Panama, it migrated into Central America as far as Guatemala. A related genus, Glyptotherium, reached the southern region of the modern USA about 2.5 million years ago. They became extinct about 10,000 years ago, probably from over-hunting. The native human population in their range is believed to have hunted them and used the shells of dead animals as shelters in inclement weather.
Glyptodon measured over 3.3 m (10.8 ft) in length and weighed up to 2 tons. It was covered by a protective shell composed of more than 1,000 2.5 cm-thick bony plates, called osteoderms or scutes. Each species of glyptodont had its own unique osteoderm pattern and shell type. With this protection, they were armored like turtles. Unlike most turtles, glyptodonts could not withdraw their heads, but instead had a bony cap on the top of their skull. Even the tail of Glyptodon had a ring of bones for protection. Such a massive shell needed considerable support, evidenced by features such as fused vertebrae, short but massive limbs, and a broad shoulder girdle.
The nasal passage was reduced with heavy muscle attachments for some unknown purpose. Some have speculated that the muscle attachments were for a proboscis, or trunk, much like that of a tapir or elephant. The lower jaws were very deep and helped support massive chewing muscles to help chew coarse fibrous plants; a distinctive bar of bone projects downwards on the cheek, extending over the lower jaw, perhaps providing an anchor for powerful snout muscles. Another suggestion, made by A.E. Zurita and colleagues, is that the large nasal sinuses could be correlated with the cold arid climate of Pleistocene South America