January 7, 2010 on ITN News:
A prehistoric footprint left by an ancestor of the dinosaurs could lead to a radical change in theories of how animals evolved.
Polish scientists have discovered footprints left by a four-legged animal called a tetrapod 397 million years ago in the Swietokrzyskie mountains in southern Poland.
The footprints, left by a creature about 2.5m long, are 18 million years older than the earliest known examples of fossilised bones of tetrapods.
According to existing fossil evidence it was thought that tetrapods diverged from the group of large fish called the elpistostegalians around 387 million years ago, but the new discovery turns this theory on its head.
At the time the footprints were made, the region was a seashore, whereas previous fossil findings of four-limbed vertebrates have been in river deltas and lakes.
The seashore could have been a tempting source of new food for ocean-dwelling animals and eventually tempted them to walk on land.