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 . Amphibians such as the Axolotl ingest rocks that are presumed to be gastroliths. Apparent microgastroliths have also been found in frog tadpoles. Ingestion of silt and gravel by tadpoles of various frog species improves buoyancy control.