gastroliths

Gastroliths are stones swallowed by some animals to aid digestion. They are typically housed in a muscular stomach called a gizzard, where the stones act as grinding agents to break down tough plant matter and hard seeds, increasing the efficiency of mechanical digestion. In birds, gastroliths reside in the ventriculus and can be exchanged as needed to suit dietary requirements. Similar stones have been observed in some reptiles, and in general they are associated with herbivorous or omnivorous feeding strategies that benefit from grinding action.

In the living world, gastroliths occur across a range of species. Birds are the most familiar example, using gastroliths to process ingested food within the gizzard. Among reptiles and other vertebrates, instances are reported less frequently but noted as part of digestive adaptations in certain lineages. The stones are typically small, smooth, and rounded from repeated abrasion within the gizzard.

The fossil record preserves gastroliths as evidence of past digestive strategies. In paleontological contexts, smooth, polished stones found within or near the abdominal region of dinosaur fossils have been interpreted as gastroliths. They are particularly associated with sauropods, where clusters of stones suggest a gastric mill, though not all dinosaur species show this feature. Distinguishing true gastroliths from stones displaced during burial requires careful contextual analysis.

Gastroliths contribute to understanding of feeding biology, digestive physiology, and ecological adaptations across evolutionary history. They illustrate how convergent mechanical digestion evolved in diverse vertebrate lineages.