By Adam Rutherford, GuardianUK
Life on Earth began in the seas, around 4bn years ago. Skip forward a few billennia and the oceans are teeming with creatures, but until around 400m years ago the land of our largely blue planet remained bereft of large animal life. The step in that perfect unbroken chain of evolution that resulted in your existence on terra firma began with a fishlike ancestor wading out of the shallows, and finding that breathing air had its own advantages.
What took those first steps on land, and when, remain two of the great questions in evolution. We know that four-legged animals were firmly established 365m years ago, adapted for a life primarily on Earth. And in 2006 we discovered the perfect transitional beast, Tiktaalik, who lived 10m years earlier. This ugly brute is a scientific beauty, with some fish-like traits (such as gills), some land-lubbing traits (such as lungs), and some that were in between (a wrist joint connecting to fins). But Tiktaalik did not have feet, was not a tetrapod. It was capable of waddling and pushing itself up above the surface to suck in some air. But its limbs, while on an evolutionary path to becoming legs, were definitely fins.
Today in a new paper in Nature, a team led by Swedish researcher Per Ahlberg has forced a seismic shift in this fascinating story. In a miserable disused Polish quarry researchers Grzegorz Niedzwiedzki and Piotr Szrek stumbled across a set of footprints stamped into rock that is securely dated to be 395m years old. And they are certainly footprints: there are visible toe holes. These new tracks suggest that the current model of the transition from water to land is significantly wrong both in time and environment. And there's nothing more exciting in science than when what we knew turns out to be wrong. This creature had toes, 20m years before anything we currently know had toes. Unlike Tiktaalik, it was walking the walk.
More:
http://www.guardian.co.uk/commentisfree/2010/jan/06/fossil-footprints-land-animal
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