Gastroliths have only rarely been found in association with fossils of theropod dinosaurs and a trituration of their food with the stones is not plausible. Aquatic animals, such as plesiosaurs, may have used them as ballast, to help balance themselves or to decrease their buoyancy, as crocodiles do. More research is needed to understand the function of the stones in aquatic animals. While some fossil gastroliths are rounded and polished, many stones in living birds are not polished at all. Gastroliths associated with dinosaur fossils can be several kilograms in weight. Stones swallowed by ostriches can also reach a length of more than 10 cm.