Armored Amphibian Fossils From China Suggest a Creature That Never Left the Sea

Two fossils found in China point to an amphibian that spent its entire life in the ocean, according to ScienceAlert. No amphibian alive today lives in the sea, since their porous skin generally cannot cope with salt.

Geologist Lipin Diao and colleagues describe the animal as a new species, Gerrothorax maritimus, in the journal Nature Ecology & Evolution.

What exactly was found?

Two fossils turned up in Guanling County, in a rock layer about 237 million years old that is part of the Guizhou Triassic Fossil Sites. Local farmers discovered them. The better-preserved specimen measures at least 73.7 centimeters (2.4 feet) along its preserved midline, even though a few tail bones are missing.

The animal had a flat, chunky body covered in plates of hard armor, which are well preserved. No living amphibian has anything like it.

Where did it live?

During the Late Triassic, the area was entirely under seawater. The animal appears to have shared a marine ecosystem with ichthyosaurs, crinoids and turtles. Both fossils lay more than 30 kilometers (18.6 miles) from any possible nearby islands, so the animals may never have left the water.

Co-author Ryosuke Motani, a paleontologist at the University of California, Davis, said researchers there had mostly studied marine reptiles and fish, so an amphibian is an unusual addition.

Could the bodies have drifted out to sea?

The team considered it and found it doubtful. Both skeletons are almost fully intact, down to the limbs, and the researchers noted that limbs are among the first parts a carcass loses at sea. Motani explained that carcasses that do not sink right away tend to dry out and shed limbs. Because even the fingers were preserved, he said, the animals probably died near where they lived.

What do the bones say about seawater?

The team also analyzed strontium, a trace element that builds up in bones. The ratio of two forms of it, 87Sr and 86Sr, varies on land with the local rock, while the ocean has about the same value worldwide. The ratio in these bones matched Triassic seawater, not the rock around the fossils. The authors concluded that both animals most likely grew up drinking seawater.

They also wrote that the armor would have stopped water from soaking in through the skin, so the animal would have had to drink and absorb water through its digestive tract, unlike most amphibians today.

Why does it matter?

Amphibians are best known for moving between land and water, and none is known to live in the ocean now. This find suggests one ancient lineage went fully marine, which broadens the picture of what amphibians once did and of the animals that shared Late Triassic seas.

The conclusion rests on two specimens from a single area. Its flat body, weak limbs and heavy armor would have made walking on land hard, if it went ashore at all, according to the report.

Around Prague, based on reporting by ScienceAlert