A fossil found in China shows that an amphibian once lived its whole life in the sea, New Scientist and BBC Newsround report. Scientists named the animal Gerrothorax maritimus. It lived about 237 million years ago, in the Triassic period.

Amphibians such as frogs and newts have thin skin that lets salt water in, which is usually deadly to them, New Scientist reports. None of the roughly 8,000 kinds alive today live fully in the sea. Scientists think this animal survived because of the hard plates of armor on its body.

Farmers in Guizhou province collected two nearly complete skeletons in 2004, BBC Newsround reports. The largest was nearly 74 centimeters long, about the length of a small guitar. New Scientist says the fossil was found in what is now a national park for rocks and fossils in Guanling county.

To show the animal really lived in the sea, scientists tested the chemistry of its bones, the outlets report. It matched seawater. The rocks it was found in formed at least 30 kilometers from land. "It was a flat animal that lived on the sea floor," said Ryosuke Motani of the University of California, Davis, New Scientist reports. Its wide mouth suggests it lay still and sucked in prey that came close.

Its closest known relative lived in fresh water, New Scientist reports. Motani said that freshwater animal "happened to have the equipment needed to colonise the sea - the body armour." The study was published in the journal Nature Ecology & Evolution, BBC Newsround reports.

What we know: The fossil is the first evidence of an amphibian that lived fully in the sea.
What we don't: Exactly how it breathed and fed, since its soft body parts were not preserved.