Scientists say they have discovered the footprints of the first creature which evolved from being a fish to being able to walk on land.

They say this happened at least 18 million years earlier than they previously thought. The footprints of a crocodile-like creature were found in the mountains of southern Poland.

It means experts will have to rethink how life developed on Earth. The science journalist, Dr Henry Gee says they might even have to re-write books.