Two exceptional 237-million-year-old fossil skeletons discovered in China’s Guizhou Province have revealed an ancient, heavily armored amphibian that lived entirely in the ocean.
The newly identified species, named Gerrothorax maritimus, measured at least 73.7 cm long and possessed a broad, flattened body protected by thick bony armor. Researchers from the University of California, Davis, Peking University, and the Geological Museum of Guizhou detailed the discovery in Nature Ecology & Evolution, noting that the remains date back to the Late Triassic period.
While more than 8,000 amphibian species live today, none are known to spend their entire lives in marine environments. This area is part of an ecosystem that we’ve been looking at and trying to reconstruct,
said study corresponding author Ryosuke Motani, a professor in the Department of Earth and Planetary Sciences at UC Davis.
We’ve been mostly studying marine reptiles and the fish from this place, but now we also have this amphibian, and it’s a sort of very unusual member of the lineage.
The fossils were uncovered in a region that was once submerged beneath an ancient ocean at least 30 kilometers from the nearest island. Chemical analysis of strontium isotopes in the bones closely matched ocean water conditions of the Triassic period, confirming that the animals inhabited a marine environment.
Its heavy build and skull structure suggest it rested on the seafloor as an ambush hunter, with a jaw that lifted upward like a toilet seat to unleash a suction attack on fish and other small creatures.
Modern amphibians struggle in saltwater because their skin is permeable, which makes it difficult to maintain the right balance of water and salt in their bodies.
For Gerrothorax maritimus, researchers suggest that its extensive bony armor restricted water movement through the skin. The animal likely took in seawater through its mouth while relying on gills to help eliminate excess salt.
The preservation of delicate skeletal features further confirmed the animals died near their natural habitat rather than washing out to sea. Because the bones were preserved with most elements still in their original positions, including the toe bones, the researchers concluded that it is unlikely the carcass drifted in from land.