Washington, Nov 10 : Palaeontologists have discovered a unique fossil in Germany that depicts 290 million years old food chain when sharks used to eat amphibians who in turn ate fishes in the great lakes of the Earth.

The new fossil discovery has the preserved remains of a fish, which was eaten by an amphibian, which was then eaten by a shark. Thus, it provides the first ever snapshot of an ancient, three-level, vertebrate food chain.

The fossilized trio lived 290 million years ago in the shallow coastal waters of a freshwater lake in the Saar-Nahe Basin of southwestern Germany. The lake had previously been linked to the sea but was landlocked for millions of years before the three animals lived and died.

An animal's last meal is very rarely preserved, because corrosive acids quickly erupt from the decaying stomach, dissolving any food remnants before fossilization can take place.

"But in this case, the shark didn't just die and sink down and decompose," National Geographic News quoted Jürgen Kriwet, a palaeontologist from Berlin's Museum of Natural History and co-author of a new study on this fossil, as saying.

"It was probably still alive when it got trapped under a rapid influx of sediment from surrounding hills," he added.

Several pieces of evidence suggest that the animals must have formed part of a single food chain, with the orientation of the fossils fitting perfectly.

Permian-period sharks, like the one in the fossil, were only 19 inches (50 centimetres) long and ambushed their prey, swimming up from behind and swallowing it whole.

"The fossilized amphibian is also in exactly the right position to suggest it had been eaten as it was lying tail-first along the shark's digestive tract," said Kriwet.

"Also, the fish remains are fully enclosed within the amphibian's outer covering of scales," he added. This according to him confirms that it was indeed eaten by the amphibian and not by the shark.

Before the shark ate it, the amphibian had caught a young fish known as an acanthodian, which was covered in bony spines.

"The fish is situated in quite the correct area of digestive tract of the amphibian," said study co-author Ulriche Heidtke. "It clearly shows the hallmarks of digestion, such as disintegration," he added.

"Evidence also points in favour of the food chain theory because if the shark had eaten the fish first and then the amphibian, they would be placed one after the other in the shark's stomach," said Kriwet.

According to John Maisey, a curator of palaeontology at the American Museum of Natural History in New York, "Well-documented examples of predator-prey relationships such as this are very rare."

"Such fossils allow scientists to reconstruct parts of extinct food chains," Maisey added.  (ANI)