Armored amphibian fossils point to life at sea 237 million years ago

Two nearly complete fossils of Gerrothorax maritimus indicate that the armored amphibian lived in seawater about 237 million years ago, researchers say, making it the first known fully marine member of the amphibian stem lineage. The skeletons were recovered from Late Triassic rocks in southern China, in an area that was then covered by sea. The study, published in Nature Ecology & Evolution, identifies the species from the fossils and argues that it lived and died in a marine environment rather than being washed there after death. Researchers point to two lines of evidence. The skeletons remained nearly intact, including small bones in the limbs, which the team says makes long-distance transport of carcasses from freshwater unlikely. Strontium isotope ratios in the fossil bones also match those associated with Triassic seawater. The researchers interpret that chemical signature as evidence the animals grew up in the ocean. The findings add an unusual marine adaptation to the fossil record. Living amphibians generally cannot tolerate seawater because their permeable skin plays a role in water, gas and salt exchange. The researchers propose that Gerrothorax’s heavy body armor...