birds, seals and sea lions. Domestic fowl require access to grit. Stones swallowed by ostriches can exceed a length of 10 centimetres (3.9 in)[citation A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In other species the rocks are ingested and pass through the digestive system and are frequently replaced. The grain size depends upon the size of the animal an A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In other species the rocks are ingested and pass through the digestive system and are frequently replaced. The grain size depends upon the size of the animal and the gastrolith's role in digestion. Other species use gastroliths as ballast. Particles ranging in size from sand to cobble have been documented. The ingestion of gastroliths is known as lithophagy. Among living vertebrates, gastroliths are common among crocodiles, alligators, herbivorous birds, seals and sea lions. Domestic fowl require access to grit. Stones swallowed by ostriches can exceed a length of 10 centimetres (3.9 in). Apparent microgastroliths have also been found in frog tadpoles. Ingestion of silt and gravel by tadpoles of various anuran (frog) species has been observed to improve buoyancy control. Some extinct animals such as sauropod dinosaurs appear to have used stones to grind tough plant matter. A rare example of this is the Early Cretaceous theropod Caudipteryx zoui from northeastern China, which was discovered with a series of small stones, interpreted as gastroliths, in the area of its skeleton that would have corresponded with its abdominal region. Aquatic animals, such as plesiosaurs, may have used them as ballast, to help balance themselves or to decrease their buoyancy, as crocodiles do. Research indicates that the presence of gastroliths in elasmosaurid plesiosaurs differs from that of the short-necked plesiosaurs. While some fossil gastroliths are rounded and polished, many stones in living birds are not polished at all. Gastroliths associated with dinosaur fossils can weigh several kilograms. Certain crayfish store gastroliths in their stomachs. Crayfish living in freshwater store these gastroliths as the presence of calcium is limited in freshwater. These gastroliths serve as a calcium source for molting.

Gastrolith Gastroliths, or gizzard stones, are small rocks kept by an animal inside its stomach or at an early part of the alimentary canal. The function of these is to mash up the food so digestion takes place faster. Typically, animals which do this do not have suitable teeth for grinding, and the gastroliths are a good substitute for this. A second function, in aquatic animals, is that gastroliths can be used for ballast to make diving easier. Identification Several pieces of evidence are needed to show that a rock was used by a fossil animal to aid its digestion. First, the stone must be unlike the rock found in its geological vicinity. Secondly, it should be rounded and polished, because inside a gizzard any genuine gastrolith would grind against other stones and fibrous materials, like the action of a rock tumbler. Lastly, the stone must be found with the fossils of the animal which ingested it. Occurrence Among living vertebrates, gastroliths are common among crocodiles, alligators, herbivorous birds, seals and sea lions. Domestic fowl need access to grit. Stones swallowed by ostriches can exceed a length of 10 centimetres (3.9 in).

and leaves. Many modern birds swallow stones that help them grind their food. e Eggs. Fossilized eggs … and they rely on intestinal bacteria to help them digest their food. Most human intestinal bacteria are … reptiles do not chew their food very well before swallowing it. Crocodilians swallow stones (stomach stones