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Previously, researchers suggested that this iron-rich material was also responsible for the striking orange to brown color of many rodents' incisors.

Their large mouths, which can open up to 180 degrees, reveal large canines and incisors used primarily for defense.

When the singer and songwriter Adrianne Lenker was 21, she was involved in a bike accident that knocked out one of her incisors.

Additionally, burnt plant remains from the sites and distinct dental-wear patterns on the individuals' upper incisors indicate that tubers -- or plants that grow underground, such as potatoes -- likely were the most prominent subsistence resource.

The gorilla, for example, needs strong muscles near the ear to chew fibrous vegetable matter, while the chimpanzee uses its incisors to bite into tasty fruit.