China discovery reveals first fossil evidence of fully marine amphibian

Paleontologists have identified the first known fossil evidence of an amphibian species that lived its entire life in the ocean. The discovery, centered on two nearly complete skeletons of Gerrothorax maritimus, was made in the Guizhou province of China.

Living approximately 237 million years ago during the Late Triassic period, this ancient creature was roughly 75 centimeters long with a flattened, disc-shaped body. Unlike modern amphibians, which are largely restricted to freshwater or land due to their permeable skin and sensitivity to salt, Gerrothorax maritimus possessed a bony armor. Researchers suggest this armor may have helped mitigate osmotic stress and dehydration in a marine environment.

The specimens were found in marine sediments alongside fossils of ichthyosaurs, large marine reptiles that were apex predators of the era. Based on its skull shape and throat structure, scientists believe the amphibian was a bottom-dwelling ambush predator that captured prey, such as fish or worms, by using suction to pull them into its wide mouth.