Plant-eating dinosaurs had a problem. Their tiny mouths were nowhere near big enough to chew up the huge amounts of leaves and ferns they had to eat. Some - like sauropods - barely chewed at all. So how did they break down their food?
The answer was rocks. Plant-eating dinosaurs deliberately swallowed stones, which sat in a muscular pouch in their stomach. As the stomach contracted, the stones ground around inside, mashing up plant matter the same way teeth would have done. These stones are called gastroliths, and we find them in dinosaur skeletons regularly, polished smooth from years of use.
It’s not just a dinosaur thing. Modern birds - chickens, ducks, ostriches - still swallow small stones for the same reason. Crocodiles do too. The dinosaur trick is still working today.
