Instead of small beaks to peck with, like the birds we know today, in the time of the dinosaurs birds had strong jaws and teeth.

Now one of these ancient birds has given a unique insight into the diet of these creatures thanks to traces found in its fossilised vomit.

The remains of a fish that had been swallowed whole were discovered alongside the fossils of a 120-million-year-old bird, proving ancestors of modern birds were fish-eaters.

The remains of a fish that was swallowed whole were discovered alongside the fossils of a 120-million-year-old bird (pictured). This is the first evidence the cousins of the ancestors of modern birds were fish-eaters

From the oldest known bird, the Archaeopteryx, which lived in the Jurassic, until the mass extinction that closed the Cretaceous 66 million years ago, the world was populated with toothy birds.

But small bird-like dinosaurs vanished along with giants such as Tyrannosaurus and Triceratops after a huge meteor smashed into the Earth 66 million years ago.

THE WORLD'S OLDEST BIRD VOMIT A pellet is the name given to the mass of undigested parts of a bird's food, Some bird species occasionally regurgitate these pellets. The contents of a bird's pellet depend on its diet. They can include the exoskeletons of insects, indigestible plant matter, bones, fur, feathers, bills, claws, and teeth. Advertisement

Now a group of scientists from the Chinese Academy of Sciences, Beijing, have published a paper revealing the diet of a group of these bird-like dinosaurs.

The bird was part of a group called enantiornithes, the most successful clade of Mesozoic birds, and the sister group of the ornithuromorpha.

The latter clade gave rise to modern birds.

This is the first clear evidence of what these ancient bird-like dinosaurs ate, according to the researchers.

'The feeding habits of enantiornithines have remained unknown because of a lack of fossil evidence,' the authors said.

The bird was part of a group called enantiornithes, the most successful clade of Mesozoic birds, and the sister group of the ornithuromorpha. It was discovered in the Liaoning province, China (pictured)

The fishy remains were found in a 'spindle-shaped cluster' beneath the right humerus, the researchers said (diagram pictured). This is just one of just two fossils that indicate some of the enantiornithine birds ate fish

'The new enantiornithine, like many modern piscivores and raptors, seems to have swallowed its prey whole and regurgitated indigestible materials such as bones, invertebrate exoskeletons, scales, and feathers.'

The remains appear to be a packed-down 'pellet' of indigestible food the Cretaceous bird vomited just before it died.

This is just one of just two fossils that indicate some of the enantiornithine birds ate fish.

In a separate study last month, paleontologist Derek Larson from the University of Toronto in Canada and his colleagues determined teeth might have been a liability a massive asteroid struck the Earth 66 million years ago.

'The new enantiornithine, like many modern piscivores and raptors, seems to have swallowed its prey whole and regurgitated indigestible materials such as bones, invertebrate exoskeletons, scales, and feathers,' the researchers said. The fossils are pictured in situ

Pecking at seeds may have helped ancestors of modern birds survive the cataclysm that wiped out the dinosaurs, they said.

Small bird-like dinosaurs vanished along with giants such as Tyrannosaurus and Triceratops after a huge meteor smashed into the Earth 66 million years ago.

But some of them survived until the end of the Cretaceous period and instead evolved into the birds that populate the world today. They were the seed-eaters with toothless beaks.