The vomit was found to contain the remains of dozens of belemnites - squid-like shellfish that lived in abundance in the seas around what is now Britain.
The belemnites were eaten in great numbers by ichthyosaurs, large marine reptiles (related to land-dwelling dinosaurs) common in the warm seas of the Jurassic era, similar in size and shape to dolphins.
Having eaten dozens of belemnites, an ichthyosaur would regurgitate their indigestible bullet-shaped shells in much the same way that an owl does after eating a mouse whole.
It is these shells that have been discovered in the fossil vomit.
"We believe that this is the first time the existence of fossil vomit on a grand scale has been proven beyond reasonable doubt," says geologist Professor Peter Doyle, of the University of Greenwich.
| The ichthyosaur would regurgitate the belemnites' indigestible shells.
| University of Greenwich
"The Peterborough belemnite shells, viewed under a powerful scanning electron microscope, have revealed ‘acid etching' marks caused by digestive fluids from the gut of a marine reptile, proving that a predator had eaten the belemnites.
"The fact that most of these belemnites were juveniles reinforces our view that they did not die of old age."
"It is highly unlikely that these shells passed through the ichthyosaur's intestines and were excreted as droppings, as they would have damaged the soft tissue of the reptile's internal organs," continued Professor Doyle.
"The only alternative is that the shells were vomited out, in much the same way that modern-day sperm whales regurgitate the indigestible beaks of squid they have eaten."
This research was prompted by the discovery of a mass of 180 million-year-old belemnite fossils discovered in the 1990s on what has become known as the ‘Dinosaur Coast', near Whitby in Yorkshire, England.
The large concentration of belemnite fossils in the Peterborough clay quarry suggests that 160 million years ago the area was a shallow-water, coastal feeding ground for belemnites.