the eyes of vertebrates. It results in colorblindness and low acuity vision in dim-light conditions and blindness in bright-light conditions. Xenarthrans most likely only used vision at night, during twilight, and while in burrows. However, the understory of South America's rainforests may have been dark enough during the day to facilitate limited vision for species that dwelled there. Extinct glyptodonts' tough carapace and large body size might have compensated for their inability to see approaching predators. Ontogeny Immature individuals of Glyptotherium texanum from juveniles to adults found in Blancan localities in Arizona preserve a nearly complete growth series, one of the few known in glyptodonts. The teeth of Glyptotherium preserve hypselodonty, where the teeth do not stop growing. In the juveniles, fully articulated osteoderm-to-osteoderm contact is already known, even at their age. Growth of the osteoderms continued from juveniles to sub-adults and ceased when osteoderms became ankylosed. The lateral profile of juvenile's carapaces are gently convex into the high arched carapaces of adults. Another ontogenetic change is in the sulci and peripheral figures of the osteoderms; the central figures are largest relative to the sulci in newborns and juveniles, but this ratio becomes lower in adults. In G. cylindricum however, the osteoderms grow much faster and the sulci are much smaller. The osteoderms are also relatively thicker in juvenile Glyptotherium individuals compared to adults. Sexual dimorphism Individuals of Glyptotherium texanum found in Blancan localities in Arizona preserve sexual dimorphism between male and female individuals. The caudal aperture, large conical osteoderm that protect the base of the tail, of males and females differ in that the marginal osteoderms of males are much more conical and convex than those of females. Even in the carapaces of newborn Glyptotherium, the marginal osteoderms are either conical or flat, which enables their sex to be determined. Osteoderms and protection Osteoderms of Glyptotherium are made of a cancellous trabecular core in between two compact layers. Each hexagonal osteoderm is joined to the adjacent osteoderms with sutures, creating a large, robust carapace similar to those in modern animals. However, the carapaces of glyptodonts like Glyptotherium were far less flexible than those of modern armadillos. The trabecular core was made up of struts used for support with an average thickness of 0.25 mm, these struts making up the central support of the osteoderm. Mechanical analyses revealed that smaller load areas, representing sharper objects, cause higher stresses than those