By Victoria Gill
Science reporter, BBC News
The team examined how marine creatures changed during decay
By watching fish as they rot, scientists have discovered "patterns" that could help interpret some of the oldest and most important fossils.
The "very smelly" study revealed how primitive marine creatures changed as they decayed.
The researchers identified particular patterns of deterioration that should help scientists more accurately identify very early marine fossils.
They published their findings in the journal Nature.
Dr Rob Sansom from the University of Leicester, UK, who led the study, said that examining fossils was very similar to forensic analysis - putting together a scientific reconstruction of something that happened in the past.
"Unlike forensics, however, we are dealing with life from millions of years ago," he said.
"What we want to get at is what an animal was like before it died and, as with forensic analysis, knowing how the decomposition that took place after death altered the body provides important clues to its original anatomy."
This applies particularly to animals preserved as soft tissue remains, which is all that is left of some of the earliest creatures in the fossil record - marine creatures that lived up to 500 million years ago.
These earliest known chordates had no skeleton, but, in some exceptional conditions, their soft bodies were fossilised and preserved.
What the researchers wanted to find out was exactly how these animals' forms might have changed after they died and before they were fossilised.
Dr Mark Purnell, who was also involved in the study, explained that this involved "some very unpleasant experiments".
He and his colleagues studied some primitive marine vertebrates, including lampreys. They also examined some close relatives of vertebrates.
They placed the dead creatures in clear containers and watched how each of the specimens changed as it rotted.
The team discovered that many defining characteristics - some of which biologists use to identify fossils - were fundamentally altered by decay.
Features including the patterns and shapes in the animals muscles changed dramatically as they decomposed.
The scientists traced these changes and described patterns that they hoped scientists would use to better interpret some of the most ancient marine fossils.
"We need to understand how they decayed if we're going to put them in the right place in the tree of life," said Dr Purnell.
He concluded: "The work doesn't appeal to everyone, but it's worth the effort."