Teeth are like tiny biological time capsules. They tell stories about ancient diets and environments long after their owners have died and landscapes have changed.
After bones break down, tooth enamel stays hard and unchanged, even in fossilized teeth that have been buried under sediment and rock for millions of years and are now being uncovered by erosion or excavation.
Tooth enamel forms when an animal is young, and it remains chemically stable for the rest of that animal’s life. The food an animal eats and the water it drinks during its youth leave chemical signals within the enamel.
Because of that, hidden within the enamel of fossilized teeth, scientists can find traces of extinct forests, expanding savanna grasslands, shifting climates and evolving animal communities.
A small group of oryx forage in the open savanna of Awash National Park in Ethiopia, with scattered acacia trees and dry grasses illustrating the park’s semi-arid environment.
Zelalem Bedaso
Over the past 30 years, my colleagues and I have been analyzing chemical traces in fossil teeth from Ethiopia’s Afar region in the East African Rift Valley – often referred to as the cradle of humanity – to uncover what animals ate there millions of years ago, around the time early human ancestors were evolving, and what the world looked like around them.
These clues from ancient meals are enabling scientists to reconstruct pictures of entire ecosystems, including forests, wetlands and grasslands that existed at the time. It’s a reminder that in a very real sense, organisms are what they eat.
Traces of ancient diets in fossil teeth
To determine which plants ancient animals ate, my colleagues and I collect a small amount of enamel powder from fossilized teeth. We then analyze this powder in the laboratory using specialized instruments that detect chemical signals preserved in the enamel.
Trees and grasses have different ways of using photosynthesis to convert sunlight into energy. These methods leave distinct chemical patterns in plant tissues, which then become incorporated into the teeth of animals that eat those plants.
By examining these chemical patterns in tooth enamel, we can determine whether animals primarily fed on trees and shrubs or on grass, providing insight into the vegetation that once covered the ancient landscape.
The author conducts fieldwork in the East African Rift, collecting samples from ancient lake and river deposits.
Courtesy of Zelalem Bedaso
We can then figure out how an environment changed over time by collecting fossil teeth from different rock layers. Each layer formed at a different time in the past, so teeth found in deeper layers are typically older than those closer to the surface.
By analyzing tooth enamel from fossils across these layers, we can compare the chemical signals preserved in the teeth and see how animal diets and the plants growing…
