FOSSILS REVEAL FULLY MARINE AMPHIBIAN IN TRIASSIC CHINA

Researchers say fossils found in China provide the first evidence of an amphibian that lived entirely at sea. They named the species Gerrothorax maritimus after analysing two nearly complete skeletons from the Late Triassic, nearly 237 million years ago. The fossils came from Guizhou province, in an area once covered by ocean. Ryosuke Motani of the University of California, Davis, called the animal “a sort of very unusual member of the lineage”. Researchers from Peking University and the Geological Museum of Guizhou also contributed to the study.

One preserved specimen measures 74 centimetres, while researchers estimate the animal reached about 0.9 metres in length. Its broad, flattened body carried bony armour, and its skull and neck bones suggest it fed by drawing prey into its mouth from the sea floor. The researchers suggest the armour may have protected it from predators and helped it survive in salt water. Tests of the bones found a chemical signature consistent with growth in sea water. Reconstructions place the fossil site at least 30 kilometres from land at the time; the area was also far from large landmasses.

The researchers say none of the more than 8,000 living amphibian species inhabits a fully marine environment. They found no earlier fossil evidence of an amphibian that spent its entire life at sea. The fossils show four legs and gills, but researchers found no evidence that Gerrothorax maritimus underwent metamorphosis. Its closest known relative, Gerrothorax pulcherrimus, lived in freshwater. Researchers also found the marine reptile Guizhouichthyosaurus alongside the amphibian fossils.