Opalized fossil remains of the stomach of a plesiosaur. The stomach contents have been fossilized by replacement of the organic matter with tiny spheres of hydrous silicon oxide (opal). This allows paleontologists to study the diet of this marine dinosaur. As well as providing insights into its feeding habits, the stomach contents may give valuable clues as to the climate in the region in which the dinosaur lived some 120 million years ago. This specimen was found in Australia and is kept at the Sydney Museum. .