The water-dwelling ancestors of modern-day mammals, reptiles and birds emerged onto land millions of years earlier than previously believed, researchers report. A set of fossilized footprints show that the first tetrapods — a term applied to any four-footed animal with a spine — were treading open ground 397 million years ago, well before scientists thought they existed. An expert unconnected with the research said the find would force experts to reconsider a critical period in evolution when sea-based vertebrates took their first steps toward becoming dinosaurs, mammals and — eventually — human beings. "It blows the whole story out of the water, so to speak," said Jenny...
