Tortoise shells are especially large and strong. They include a wide bridge that connects the upper shell (carapace) to lower shell (plastron). This substantial shell might protect them from getting trampled by grazing animals or dried out in the sun. Scientists think that ancestors of tortoises may have lived in herds of bison or wildebeest, making its armor-like shell essential. A modern tortoise also uses its shell for fighting. In male tortoises, the plastron often juts out in front in a single or double spur. Males use the spurs to ram or even flip over other males in fights over females. Getting flipped can be hazardous to a tortoise in a flat habitat like grassland or desert, where it is hard to get the leverage to right itself.

Turtles have survived changes on Earth for more than 200 million years. Yet, now more than half the remaining turtle species in the world are threatened with extinction. Threats range from habitat changes (such as destruction of wetlands), incidental capture (for example by commercial fisherman), to intentional harvest for food, pets, and other uses. Stress from multiple factors has also made turtles more vulnerable to disease. Desert tortoise populations in the United States have been decimated by an upper respiratory disease. Conservation efforts include educating the public about the danger of releasing turtles, who may be sick, into wild populations. Some fishing industries use turtle excluder devices that keep turtles out of fish nets and crab traps. Laws have regulated the harvest and sale of turtles, but their enforcement depends on individual countries. Whether turtles will make it through another million years on Earth is unknown.