The dinosaurs had only been extinct about ten million years when the Eocene (Eo - dawn; cene - recent) began. Mammals evolved larger bodies and became more diverse during the Eocene. Plant-eating mammals included ancient hooved animals called condylarths, while meat-eaters included an extinct group of dog-like beasts called creodonts. Eight-foot-high carnivorous "terror birds" also reigned during the Eocene.