for National Geographic News
About 290 million years ago, Earth's lakes were a shark-eat-amphibian-eat-fish world, new fossil evidence reveals.
The fossil provides the first ever snapshot of an ancient, three-level, vertebrate food chain.
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," said Jürgen Kriwet, a paleontologist from Berlin's Museum of Natural History and co-author of a new study on the find.
"It was probably still alive when it got trapped under a rapid influx of sediment from surrounding hills," he said.
(Related news: "World's Oldest Shark Fossil Found" [October 1, 2003].)
A Single 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.
Several pieces of evidence suggest the animals must have formed part of a single food chain.
For one thing, "the orientation of the fossils fits perfectly," Kriwet said.
Permian-period sharks—like the one in the fossil—were only 19 inches (50 centimeters) long and ambushed their prey, swimming up from behind and swallowing it whole.
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