Hominins start eating grass

The carbon isotope ratio in tooth enamel records whether an animal ate C3 plants — trees, shrubs, fruit — or C4 plants, which in Africa means tropical grasses and sedges, or animals that ate them. Early hominins such as Ardipithecus register a C3 forest signal. From about 3.5 million years ago the signal in australopiths shifts substantially toward C4, and different lineages diverge in how far. It is direct evidence of hominins moving into open habitats and exploiting a food source most primates do not touch.