Triassic Seafloor Discovery
“This area is part of an ecosystem that we’ve been looking at and trying to reconstruct,” said Ryosuke Motani, study corresponding author and professor in the Department of Earth and Planetary Sciences at the University of California, Davis. Researchers have uncovered a 237-million-year-old fossil in China’s Guizhou Province that belonged to an amphibian living entirely in the ocean.
The animal, named Gerrothorax maritimus, challenges long-held scientific assumptions about amphibian biology. An international research team from UC Davis, Peking University, and the Geological Museum of Guizhou published the findings in Nature Ecology & Evolution. Both skeletons date back to the Late Triassic period, originating from a seabed situated hundreds of miles from any major landmass.
Armor and suction attacks protected the creature
The two recovered skeletons measure nearly three feet long, matching the body mass of a modern giant salamander. Unlike the elongated shape of modern salamanders, Gerrothorax maritimus featured a broad, flattened disc-shaped body wrapped in thick bony armor. Motani noted that the heavy protective plates likely shielded the creature from large marine predators such as ichthyosaurs.
The creature possessed an upturned jaw that lifted like a toilet seat. Researchers believe the animal used this mechanism to unleash suction attacks on fish and other small creatures while resting motionless on the seafloor.
Bony armor and internal gills managed salt levels
Modern amphibians generally cannot survive in seawater because their permeable skin absorbs water and gases, leaving them vulnerable to salt. Among more than 8,000 living amphibian species, none spend their entire lives in marine environments. Gerrothorax maritimus may have bypassed this limitation through its extensive bony armor, which restricted water movement across its skin. The animal likely ingested water through its mouth and processed excess salt through retained internal gills.
Strontium isotope ratios confirm a marine lifestyle
To confirm the animal’s marine lifestyle, the research team analyzed strontium isotope ratios in the fossils, which matched ocean water signatures from the Late Triassic. The preservation of delicate skeletal structures indicates the carcasses did not drift long distances before sinking. The fossils were discovered in sediment located roughly 30 kilometers from the nearest ancient land.
Common Questions About Marine Amphibians
Why can no modern amphibians live in the ocean?
Modern amphibians rely on porous skin for respiration and hydration, which causes them to shrivel or suffocate in saltwater. Less than two percent of living amphibian species possess even a minor tolerance for salt.
How did researchers prove the ancient fossil lived in the sea?
Scientists examined deep marine sediments, the high completeness of the delicate skeletal remains, and strontium isotope signatures that matched Late Triassic ocean chemistry, according to findings published in Nature Ecology & Evolution.
Where were the Gerrothorax maritimus fossils found?
Two well-preserved skeletons were uncovered in China’s Guizhou Province by an international team involving the University of California, Davis, Peking University, and the Geological Museum of Guizhou.