From St. Paul, Minn., at a meeting of the Society of Vertebrate Paleontology
The discovery of large, polished stones inside the body cavities of some fossils of large plant-eating dinosaurs led many paleontologists to believe that the gastroliths–Greek for "stomach stones"–aided the creatures' digestion by grinding up tough vegetation. New analyses of the gastroliths in ostriches are casting doubt on that theory.
Many modern-day birds, which merely gulp their food because they have no teeth and can't chew, swallow stones that help grind grain, seeds, and vegetation in the creatures' gizzards. In ostriches, the muscle contractions in this gastric mill occur two to three times per minute, says Oliver Wings of Germany's University of Bonn.