A Flattened Amphibian That Lived Its Whole Life at Sea
Amphibian skin is permeable. This animal appears to have grown up offshore anyway.
A paper in Nature Ecology & Evolution, out 26 October 2026, names Gerrothorax maritimus from two nearly complete skeletons at Guanling, in Guizhou, China. The animal was about 74 centimetres long, flat, and armored. The authors say it is the first stem amphibian known to have lived entirely in the sea.
The dating is Late Triassic, about 237 million years ago. The rock formed dozens of kilometres from the nearest land. Strontium isotopes in the bones match seawater, which is the chemical argument that this was not a river animal washed out in a flood. It sat on the seafloor and pulled prey in with a suction-feeding mouth. A flattened ambush predator, in salt water, for its whole life.
The standing problem is the skin. Living amphibians do not do this. Their skin exchanges water and salts with whatever they are sitting in. A fully marine life, on that model, pickles the animal. Either this one had a trick the model does not include, or "fully marine" is a claim the chemistry has not quite earned.
Key Evidence
- Nature Ecology & Evolution, published 26 October 2026
- Two nearly complete skeletons, Guanling, Guizhou
- Length about 74 centimetres, dorsoventrally flat, armored
- Strontium isotopes consistent with seawater
- Palaeogeography: deposition dozens of kilometres from land
- Age about 237 million years
- Secondary reports: Sci.News and New Scientist
The Rational Explanation
"Fully marine" is an inference from isotopes and maps, not a filmed life history. A coastal animal can die at sea. A carcass can drift. Isotopes can record the water the animal drank late in life, not the water it was born in. The authors are trying to close that objection with the distance-to-land and the chemistry together. A reader should keep the objection open until the supplement has been picked over by people who do not like the headline.
What We Don't Know
How a permeable-skinned animal handled salt for a lifetime, if it did. Whether the two skeletons are the species or the exception. What the skin was actually like: armor plates do not tell you about the soft tissue between them. The paper answers "where did it live?" It does not answer "how did the physiology work?"
The Rabbit Hole
Stem amphibians already include animals that look like nothing with a pulse now. Gerrothorax itself, the freshwater namesake, is a wide, flat, upward-looking thing with a skull that opens like a trap. Putting that body plan in the open ocean is a small change of address and a large change of rules. The Triassic keeps producing animals that used a body the textbooks had assigned to one element and took it into another.