Two skeletons from China point to an amphibian that spent its whole life in salt water
Two skeletons of Gerrothorax maritimus, about 237 million years old, are the first evidence that an amphibian could live entirely at sea.
American and Chinese researchers describe a new Triassic species, Gerrothorax maritimus, in Nature Ecology & Evolution. According to UC Davis, home of lead author Ryosuke Motani, it is the first known amphibian to have lived entirely in the sea. Farmers found the two nearly complete skeletons back in 2004 in China's Guizhou province, VRT NWS reports, but only now is it clear what they represent.
The animal was almost 75 centimetres long, flat and disc-shaped, and covered in bony armour. It probably lay in wait on the seabed and sucked in its prey, UC Davis writes. The researchers infer a marine life from the sea sediments in which the fossils lay and from strontium isotopes that match the seawater of the time. Well-preserved fingers suggest the animals died where they lived rather than washing in from elsewhere.
That is remarkable: of the more than 8,000 living amphibian species, none can survive long in salt water, because their permeable skin ties them to fresh water. The researchers suspect the armour kept seawater out and that the animal processed salt through its gut and gills, though that remains a hypothesis. In a news piece, Nature calls the find a possible turning point in how amphibian evolution is understood. VRT NWS gives an age of 273 million years, while the university itself puts it at about 237 million years.