Two nearly complete fossil skeletons of Gerrothorax maritimus, identified as the first known fully marine stem amphibian, were discovered in Guizhou Province, China. The animal lived about 237 million years ago, during the Late Triassic. The study was published in Nature Ecology & Evolution on 26 October 2026.
Geological Age and Fossil Site
The Late Triassic lasted from approximately 237 million to 201 million years ago and is part of the Mesozoic Era. The Guizhou fossil site was an ancient offshore marine environment, hundreds of miles from large land masses. The fossils’ offshore burial setting and preserved limb bones support the conclusion that the animal lived at sea rather than being carried there from a freshwater habitat. No modern amphibian is known to live entirely in saltwater. Amphibians are generally associated with freshwater or coastal habitats, although some species tolerate brackish conditions. The discovery therefore provides a fossil record of a stem amphibian living fully in a marine setting.
Anatomy and Marine Adaptations
Gerrothorax maritimus was a bottom-dwelling animal about 737 millimetres, or roughly three feet, long. It had a broad, flattened body covered in thick bony armour. The armour may have provided protection from predators, including ichthyosaurs, marine reptiles of the Mesozoic Era. The animal had internal gills and other anatomical features associated with life in seawater. These features may have helped it regulate water and salt. It is thought to have hunted near the seafloor by sucking in smaller prey.
Fossil Analysis and Research Institutions
Researchers examined the fossils’ anatomy, geological setting and chemical composition, including strontium isotope measurements. The research involved scientists from the University of California, Davis, Peking University and the Geological Museum of Guizhou. Lipin Diao was the first author, and paleontologist Ryosuke Motani of the University of California, Davis, was the corresponding author.
Important Facts for Exams
- Gerrothorax maritimus lived during the Late Triassic, about 237 million years ago.
- The Mesozoic Era comprises the Triassic, Jurassic and Cretaceous periods.
- Ichthyosaurs were marine reptiles, not fish or amphibians.
- Strontium isotope measurements can be used in geological and palaeontological research.
The fossils were found in Guizhou Province, China, in deposits formed in an ancient marine environment. Gerrothorax maritimus is described as a stem amphibian rather than a modern amphibian species.
