First marine amphibian found in ancient Chinese seas

Researchers have described the first marine amphibian known from the fossil record, a flat-bodied, armoured animal that lived in the sea covering what is now southern China during the Late Triassic. The animal, named Gerrothorax maritimus, is based on a pair of nearly complete skeletons found in Guizhou Province, according to a study published on 26 October 2026 in the journal Nature Ecology and Evolution. The skeletons place the animal in salt water about 237 million years ago, long before modern frogs, salamanders and caecilians took their present forms.

That setting is what makes the find unusual. Living amphibians depend on permeable skin for breathing and drinking in fresh water, and salt water disrupts both functions. More than 8,000 amphibian species are alive today, and none of them lives exclusively in a marine environment, although a small share can tolerate brackish water for a time and must then recover in fresh water. Birds, reptiles and mammals all include species that manage without food or fresh water from land. Until this discovery, amphibians stood alone among the four-limbed vertebrate groups with no fully marine member, living or extinct.

An armoured bottom dweller

The Guizhou animal measured 74 centimetres long and had a flattened, disc-shaped body covered almost completely in bony armour. Its skull was flat and wide, with a large mouth lined with many small conical teeth. The shape of the mouth and throat points to suction feeding, a method in which an aquatic animal expands its mouth cavity quickly to drop the pressure inside and draw water and prey in. The researchers describe the animal as a bottom-dwelling ambush feeder that waited on the sea floor and struck at passing prey, a habit comparable in outline to the carpet sharks known as wobbegongs that live today.

Size alone set the animal apart from most living amphibians. Ryosuke Motani, a palaeobiologist at the University of California, Davis, and a co-author of the study, said the animal was roughly comparable in body mass to a giant salamander, but far chunkier in shape. The armour probably mattered for more than feeding. The skeletons were found near fossils of Guizhouichthyosaurus, a large marine reptile and apex predator of the same seas, and a bony shell would have offered protection against such hunters. The reconstruction released with the study shows a spiky, toothy animal resting on the sea floor, with a fish close to its open mouth.

How the team placed it in the sea

The case for a fully marine life rests on where the fossils were found and on chemical evidence preserved in the bones. The skeletons were recovered from rocks formed from ocean sediment, in an area that lay far from any large land mass at the time. Their excellent preservation also argues against a long journey after death. Motani said carcasses at sea tend to lose limbs and dry out unless they sink to the bottom quickly, and these animals kept even their fingers intact, which suggests they died near where they lived.

The team also measured strontium isotopes in the bones, a chemical signature that reflects the water an animal lived in. The levels matched seawater of the period, and the researchers write in the paper that the creatures grew up drinking the seawater. Taken together with the location of the finds, the evidence points to an animal that spent its life in the sea rather than one washed in from a river or shoreline. The fossils are held in the collection of the Geological Museum of Guizhou, and the study team included researchers from that museum, Peking University and the University of California, Davis.

Motani summed up the result plainly. "The most important finding is that there was an early amphibian that lived in the sea full-time," he said. Steve Brusatte, a palaeontologist at the University of Edinburgh who was not involved in the study, called the result potentially revolutionary, telling Nature: "If this Triassic amphibian, Gerrothorax, really was fully marine, then it is a game-changer."

Why armour may have opened the ocean

The researchers propose that armour changed how the animal handled salt. In a typical amphibian, the skin exchanges water, gas and salt with the surroundings, a system that fails in seawater. A near-complete bony covering would have limited that exchange through the skin and pushed the work of taking in water and shedding salt onto the mouth, gut and gills, which can adapt to salt more readily. Other members of the Gerrothorax lineage also had gills, and the team argues that the combination of armour and gills prepared this lineage for life in salt water in a way that soft-skinned amphibians could not match.

The animal belonged to the temnospondyls, an early branch of the amphibian line that falls outside the living groups. Its existence does not mean that modern amphibians could make the same move, and the authors do not claim that the species survived beyond its Triassic seas. What it does show, reported by Nature, is that the barrier between amphibians and the ocean was crossed at least once in deep time, by an animal built very differently from the frogs and salamanders familiar today.

Further detail on the discovery is available in the Nature report on the find and in Popular Science coverage of the fossils, which describe the skeletons, the armour and the suction-feeding habit in full. The paper itself names Lipin Diao of the Geological Museum of Guizhou as first author, with Motani and Da-yong Jiang of Peking University as corresponding authors, and records funding from the National Natural Science Foundation of China.