Now, a new study suggests that clues may have been hiding in their stomach stones all along. To investigate how dinosaurs may have used gastroliths, the research team compared the shape and wear of stomach stones from living birds and crocodilians. In plant-eating animals with powerful, muscular stomachs, gastroliths became smooth and rounded over time because they rubbed together while grinding food. In contrast, meat-eating animals tended to have stomach stones that stayed much sharper and more angular, suggesting their stomachs did not grind food as intensely. This suggests these dinosaurs may have relied on muscular stomachs to grind plant material, much like modern chickens and other birds do today.