DgcityAmong the 8,000-plus amphibian species alive today, not one is known to spend its whole life in the sea, and fewer than two percent can tolerate saltwater at all. Fossils from southwest China now show that an amphibian did exactly that, 237 million years ago.
Two exceptionally preserved skeletons, uncovered in Guizhou Province, belong to a creature named Gerrothorax maritimus. It lived in the Late Triassic in waters that were then open ocean, far from major landmasses. An international team from the University of California, Davis, Peking University and the Geological Museum of Guizhou described the find in Nature Ecology & Evolution.
The animal looked nothing like a familiar salamander. Roughly the size and body mass of a giant salamander, it was nearly a metre long but unusually broad and flattened into a disc-like form sheathed in thick bony armor. Its flattened skull suggests an ambush predator that rested on the seabed and waited for prey to pass rather than chasing it down, while the armor may have offered protection from larger hunters such as ichthyosaurs sharing the same waters.
The rocks holding the fossils have yielded a rich picture of Triassic marine life, mostly fish and marine reptiles. The new amphibian is an odd addition to that ecosystem because its living relatives are tied so firmly to fresh water and moist land. Amphibian skin and eggs generally cope poorly with salt, which is why a fully marine species was considered unlikely.
That assumption is what the discovery overturns. The completeness of both skeletons lets researchers reconstruct the body with confidence rather than inferring habits from fragments, and the open-ocean setting makes a coastal or freshwater explanation difficult to support.
The researchers note that the Late Triassic world these animals inhabited was still recovering from earlier upheavals and was home to a diversified array of marine reptiles that might seem to leave little room for a slow, bottom-dwelling amphibian. A heavily armored ambush strategy would have let Gerrothorax occupy a different niche, feeding opportunistically rather than competing head-on with faster swimmers.
The find adds to a run of striking fossil work emerging from southern and western China, where fine-grained marine deposits preserve anatomical detail lost in most rocks. It also raises a fresh question: if one amphibian lineage solved the saltwater problem, what pressures drove it into the open ocean, and why has nothing like it survived into the modern fauna?
