The first amphibian that lived entirely at sea swam 237 million years ago — and it rewrites the family rules

Amphibians are the 'double life' animals, splitting their time between water and land — and no living species, out of more than 8,000, tolerates the sea. Two nearly complete fossil skeletons from southwestern China now show that at least one ancient amphibian made the ocean its whole home. The new species, Gerrothorax maritimus, was a flat, armoured creature about 30 inches long that lived 237 million years ago; researchers describe it this week in Nature Ecology & Evolution. 'This is potentially a revolutionary discovery,' said University of Edinburgh palaeontologist Steve Brusatte, who was not involved in the study. A rule everyone thought amphibians lived by turns out to have an exception — from deep time.