A new study published this week in the journal Proceedings of the National Academy of Sciences documents dietary shifts in herbivores that lived between 1-3 million years ago in Ethiopia's Lower Omo Valley. The research team, led by Enquye Negash, a postdoctoral researcher in the George Washington University Center for the Advanced Study of Human Paleobiology, examined stable isotopes in the fossilized teeth of herbivores such as antelopes and pigs and found a shift away from C3-derived foods, characteristic of woody vegetation, to C4-derived foods, representative of grasses and sedges. The shift happened at two distinct time periods, approximately 2.7 million years ago and 2 million years ago, when the environment of the Lower Omo Valley was transitioning to open savanna.