What do you do if you do not have good teeth, and food is hard to digest? Some herbivorous birds which have a toothless beak, such as ostriches, solve the problem with what is known as a gastric mill. Their muscular stomach is equipped with a layer of horn and contains stones which help to break up, crush and thereby also to digest food.
Giant dinosaurs from the Jurassic and Cretaceous period (200 million to 65 million years ago) such as Seismosaurus and Cedarosaurus must have had similar digestive problems. The animals, some of which weighed more than 30 tonnes, were the largest herbivores which have ever existed. Many of them had a very small head, in relation to the size of their body, and narrow, pointed teeth, which were more suited to tearing off plants rather than chewing them. At the same time, they had to digest enormous amounts of food for their rapid growth and the metabolism of their gigantic bodies. Smoothly polished stones, which were found in several cases at excavations involving skeletons of sauropods, are also interpreted as gastric stones.
However, Dr. Oliver Wings from the Institute of Earth Sciences at the University of Tübingen, and Dr. Martin Sander from the University of Bonn have shown that this cannot at least be a gastric mill such as birds, today's relatives of the dinosaurs possess. Among these the ostrich is
Source:University of Bonn