Glyptodonts were large, more heavily-armored relatives of extinct pampatheres and modern armadillos. They first evolved during the Miocene in South America, which remained their center of species diversity. For example, an Early Miocene glyptodont with many primitive features, when compared to other species, Parapropalaehoplophorus septentrionalis, was discovered at a now-elevated site in Chile and described in 2007[. When the Panama isthmus formed about three million years ago, several species, such as Glyptotherium texanum , spread north as part of the Great American Interchange, as did pampatheres and armadillos. The main feature of glyptodonts was their tortoise-like body armour that was made of bone segments 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, but unlike most turtles, could not withdraw their heads, so they developed a bony cap on the top of their skull. Even the tail of glyptodonts had a ring of bones for protection. Doedicurus even possessed a large mace-like tail that it would have used to defend itself from other Doedicurus and predators. Glyptodonts also had size on their side; many such as the type genus, Glyptodon, were the size of cars. Such heavy defenses presupposes a large, effective predator. At the time the glyptodontids evolved, the top predators in the island continent of South America were phorusrhacids, a family of giant flightless carnivorous birds. The glyptodonts were grazing herbivores. Like many other xenarthrans, they had no incisor or canine teeth, but had a number of cheek teeth that would have been able to grind up tough vegetation, such as grasses. They also had distinctively deep jaws, with large downward bony projections that would have anchored powerful chewing muscles in life.