Large lumps of pink quartzite were transported some 600 miles across what is today the American Midwest in the bellies of long-necked dinosaurs, a study concluded.
Researchers from the US explained that the giant sauropods likely swallowed the stomach stones, known as 'gastroliths', to help grind up food they had eaten.
The gastroliths ended up being buried in Wyoming's Morrison Depositional Basin during the Late Jurassic, 155–148 million years ago, when the dinosaurs perished.
The team knew the stones could not have originated there, as pink quartzite in North America is only found deposited in Idaho, Montana, New Mexico and Wisconsin.
By analysing minerals called zircons that act as little clocks, the team determined that the gastroliths formed 1.8 billion years ago, matching those from Wisconsin.