Grindless Mill?
What to do if you don't have good teeth and the food is difficult to digest? Correct: Use auxiliary tools. But did dinosaurs really serve this purpose with stones in their stomachs? New research contradicts this theory.
The giant dinosaurs had a problem: they were big, needed a lot of energy and therefore had to eat a lot. Many of them had a very small head in relation to the body and only narrow, pointed teeth, better suited to tearing than chewing plants. A good part of the nutrients therefore remained closed to them - unless they used exogenous aids. Until now, many researchers assumed that these were stones that they swallowed. In her muscular stomach, they acted like a kind of "stomach grinder".
This stomach grinder can still be found today in herbivorous birds, whose toothless beaks are also unable to properly grind the greens. Ostriches, for example, solve their nutritional problem in this way. They have a gizzard lined with a stratum corneum and contain stones that break up and grate plant matter, aiding in the digestion of food.
What applies to the comparatively small ostriches should actually apply even more to the giant dinosaurs from the Jurassic and Cretaceous periods (200 million to 65 million years ago) such as Seismosaurus and Cedarosaurus: some of them weigh more than thirty tons Animals were the largest herbivores that ever existed. They had to digest enormous amounts of food for their rapid growth and the metabolism of their oversized bodies, which would be much more efficient if the food was prepared in the mouth. Smooth stones, which in several cases were excavated together with sauropod skeletons, have been interpreted by scientists as stomach stones.
Oliver Wings from the University of Tübingen and Martin Sander from the University of Bonn have now shown that it cannot be a gastric grinder like the ones birds, today's relatives of dinosaurs, have. The two geoscientists offered ostriches – the largest feathered vegetarians – on a German breeding farm stones such as limestone, rose quartz and granite to eat, and after slaughtering the animals they examined their properties again. But these now looked completely different from the counterparts made from dinosaur stomachs, which were sometimes even sold as gastroliths. Because the ostrich stones were worn down in the gizzard within a short time and no longer contained any polish - on the contrary: their surface became rough during the experiments in the stomach."We therefore do not consider them to be the remains of a gastric grinder, as occurs in birds," comments Sander.
Occasionally, stones were found together with sauropod skeletons, but this does not happen regularly with sauropod finds, the Bonn researcher continues. And when present, their mass-to-body size ratio is much less than that of birds, which averaged one percent of their body mass, at least in ostriches.
But what else were dinosaur stomach stones for? The two researchers suspect that they may have been accidentally eaten or swallowed on purpose to improve mineral absorption. Therefore, the prehistoric lizards must have made do with other things. Bacteria in the digestive tract have to help break down the large amounts of material that is difficult to digest, but the smaller the pieces, the better they can break down the feed. So, to improve digestion, perhaps the sauropod gut was designed to hold food there for a very long time.
There is another group of dinosaurs, however, whose remains of gastric stones, according to Wings' research, correlate well with a bird-like gastric grinder: theropods. Today's birds later developed from them. © University of Tübingen
