Gastroliths make food easier to digest, essentially smashing food up, just as we do when we chew.
Over time, gastroliths inside the animal are ground down and become smooth and rounded.
Now, sauropod fossils are commonly found with smooth stones.
For years we thought these were gastroliths.
They looked just like gastroliths and were found in the area of the sauropods' stomachs.
A recent study measured the gastroliths in modern animals, in ostriches.
And the study showed that ostriches need to ingest about one percent of their total body weight in gastroliths.
But we have been able to determine that the stones found with sauropods totaled much less proportionally, less than a tenth of one percent of their body weight.
So now we are not quite sure what these sauropods' stones were used for.
It could be they were accidentally ingested as the sauropods foraged for food, that they served no real purpose.
Other researchers speculate that sauropods ingested these stones as a source of some the minerals they needed, such as calcium.
So the original hypothesis that the stones found with sauropods were gastroliths, even though it hasn't been supported, has helped us to make new hypotheses, which may eventually lead to the answer.