Prehistoric marine creatures 'more complex than previously thought'

Early marine ancestors of today's animals may have been more complex than their fossils suggest, scientists believe.

The evidence comes from forensic studies of rotting fish, which indicate many key features of creatures living hundreds of millions of years ago may have vanished before fossilisation.

As a result, scientists may have assumed the animals were simpler than was really the case.

Rob Sansom, who led the University of Leicester team, said: "Interpreting fossils is in some ways similar to forensic analysis - we gather all the available clues to put together a scientific reconstruction of something that happened in the past. Unlike forensics, however, we are dealing with life from millions of years ago, and we are less interested in understanding the cause or the time of death.

"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."

The research, reported online in the journal Nature, shows that some of the characteristic anatomical features of early vertebrate fossils have been badly affected by decomposition. In some cases, they have rotted away completely.

Knowing how decomposition has damaged fossil specimens will help scientists reconstruct the animals more accurately.

Co-author Sarah Gabbott said: "Only in the most exceptional circumstances do soft tissues, such as eyes, muscles and guts, become fossilised, yet it is precisely such remains that we rely on for understanding our earliest evolutionary relatives: half a billion years ago it's pretty much all our ancestors had."