Scientists have reported the discovery of fossil evidence for the first fully marine amphibian, a finding that challenges long‑standing assumptions about amphibian ecology. The study, conducted by researchers from the University of California, Davis, the University of Beijing, and the Guizhou Geological Museum, was published in the journal Nature Ecology & Evolution. The new species, named Gyrthorax maritimus (Arabic: غيروثوراكس ماريتيموس), is represented by two nearly complete skeletons that date to the late Triassic period, about 237 million years ago. The fossils were recovered from sedimentary deposits in a region of Guizhou Province, China, that was once part of a marine basin hundreds of miles from major landmasses. “We were mainly studying marine reptiles and fish that lived here, but now we also have this amphibian, which is a very unusual member of its group,” said Ryosuke Motani, a professor of Earth and Planetary Sciences at UC Davis and the study’s lead author. “This area is part of the ecosystem we have been studying and trying to reconstruct.” Gyrthorax maritimus was a flattened, disk‑shaped animal about three feet (roughly one meter) long. Its body was covered in bony armor, a feature that likely served as protection against predators such as ichthyosaurs. The species’ size and mass are comparable to those of the modern giant salamander, but its rounded, heavily armored form distinguishes it from extant amphibians. The researchers suggest that Gyrthorax was a benthic feeder that captured prey by suction, a feeding strategy similar to that of the modern catshark Wobegong. “It probably waited on the seafloor and, when prey approached, it would suck it in,” Motani explained. Modern amphibians are generally limited to freshwater or brackish environments because their skin is permeable to water, allowing them to absorb moisture and respire through it. This physiological trait makes it difficult for them to survive in fully marine settings. While a few species, such as the crab‑eating frog, can tolerate low levels of salinity, they lose weight in brackish water and must return to freshwater to recover. The armored skin of Gyrthorax may have prevented water absorption through the skin, forcing the animal to drink seawater orally and excrete excess salts through its gills. This adaptation would have allowed it to thrive in a marine environment. Evidence supporting a marine lifestyle includes the deep‑sea sedimentary context of the fossils, the near‑complete preservation of the skeletons (including digits), and chemical analyses of strontium isotopes that match values typical of late Triassic oceans. “The preservation of the digits indicates that the carcasses were buried quickly near their living area,” Motani noted. Until this discovery, no fully marine amphibian had been documented in the fossil record. The find expands the known ecological diversity of Triassic amphibians and provides new insights into the evolutionary pathways that enabled some lineages to exploit marine habitats.