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.