Living armadillos have banded shells with flexible joints that allow the body to bend. Glyptodon's carapace was made of the same building blocks, hundreds of interlocking bony osteoderms, but the bands were fused into an immobile dome up to about one and a half metres high. Body mass estimates run to a tonne or more in the larger species.
Mitochondrial genome sequencing from glyptodont osteoderms resolved a long argument about placement. Rather than being the sister group to all armadillos, glyptodonts fall inside the armadillo radiation, nested among living lineages. The implication is that gigantism and shell fusion arose within the group rather than defining a separate branch alongside it.
A related genus, Doedicurus, carried a heavy club of fused bone at the tail tip, and damage patterns on carapaces have been interpreted as evidence of fighting between individuals. The often-repeated claim that early South Americans used empty glyptodont shells as shelters appears in popular accounts but rests on limited archaeological evidence.