Triassic amphibian Gerrothorax maritimus identified as first fully marine species
Researchers describe a 30-inch armored amphibian from 237 million years ago that lived permanently in seawater, marking the first known marine amphibian.
A study published in Nature Ecology & Evolution details the anatomy and lifestyle of Gerrothorax maritimus, an amphibian that lived during the Late Triassic, about 237 million years ago. Fossils recovered from Guizhou Province in southwestern China are nearly complete, allowing scientists to estimate the animal’s length at roughly 30 inches (75 cm). The creature’s heavily armored body and retained gills suggest it was adapted to a fully marine environment, using suction feeding similar to modern sharks.
“We hitherto did not know of any amphibians that live in the sea full-time,” said Ryosuke Motani, a vertebrate paleontologist at the University of California, Davis and corresponding author of the paper.
Motani explained that the fossils’ preservation, including largely intact fingers and consistent strontium isotope ratios in the bones and surrounding sediment, indicates the animals grew and died at sea rather than being washed ashore post-mortem. The isotope analysis points to a specific oceanic period, supporting a marine habitat.
Modern amphibians, such as frogs and salamanders, are generally unable to tolerate seawater because their permeable skin limits salt tolerance. In contrast, G. maritimus possessed bony armor that likely protected its skin and helped it maintain buoyancy on the seafloor. The retained gill arches imply primary respiration through gills, and the large mouth suggests a feeding strategy akin to suction-feeding sharks.
The researchers note that soft tissues were not preserved, leaving uncertainties about the animal’s digestive adaptations and reproductive biology. Future discoveries of additional specimens could clarify these aspects and provide a more detailed reconstruction of its ecological context.
“For example, the two specimens we reported were found belly-side up, so it would be nice to see the back side,” Motani said. “We also want to find out about its environment in more detail to reconstruct its ecology more accurately.”