Newly uncovered fossilised fish trails dating back 400 million years may show how life-forms moved from water to land, according to Bristol researchers.
Researchers think the fish developed limbs from pectoral fins
The trails were discovered by a team at the University of the West of England in red sandstone in a Welsh quarry.
Dr Susan Marriott thinks the fossilised trails in what was once river sediment could explain the mystery.
A film has been made showing how the fish used pectoral fins to rest on, which may have developed into limbs.
Evolution of life
The site of the sandstone quarry in the Brecon Beacons was once a river, with a very different landscape from that of today with semi-desert around a wide, shallow water course instead of moors and hills, according to the research team.
The film, called Follow that Fish!, shows the researchers investigating the fossils in the sandstone.
For the film, animators from UWE's School of Animation drew moving sequences, based on the trails left behind and preserved in stone, to show how these early vertebrates may have behaved.
"One of the most important things at this time in geological history was the emergence of life from a watery environment into a land environment," said Dr Susan Marriott.
"We have found fossils and the traces of the animals that made them, from which we can make inferences about the environment the animals lived in and link it to the evolution of life on land."