Warn weather may have pushed the landlubber ancestors of some marine animals back to the sea.rnVertebrates ventured from water onto land only once, about 365 million years ago. But since then some 31 groups have gone back the other way, including prehistoric plesiosaurs and present-day whales and dolphins.rnFossils and estimates of past temperatures show that 26 of the groups took the plunge when the world was warmer than today, says Ryosuke Motani at the University of California, Davis.
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