Equid Tooth (image) University of Utah Caption The chewing surface of a fossilized upper molar from an equid -- an ancestor of zebras -- that lived in East Africa 9.6 million years ago. University of Utah researchers studied 452 fossil teeth from nine families of animals to show that between 10 million and 3 million years ago, different East African plant eaters changed at different times from a diet of trees and shrubs to a diet of warm-season grasses. Credit Kevin Uno, University of Utah Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.