Researchers Unearth Gerrothorax Maritimus, the World's First Fully Marine Stem Amphibian

Key facts

• The world's first known fully marine stem amphibian, Gerrothorax maritimus, was identified from two nearly complete Late Triassic skeletons found in Guanling County, Guizhou Province, southwestern China.
• The species lived about 237 million years ago during the Late Triassic period.
• Evidence for its fully marine lifestyle included an offshore burial setting about 200 kilometers from major land masses, preserved articulated hand bones indicating death near its living site, and strontium isotope measurements in the bones matching the seawater signature of the early Late Triassic.
• Gerrothorax maritimus had a broad, flattened body covered in bony armor plates called osteoderms, and skull and throat features suggest it was a bottom-dwelling suction feeder similar to living wobbegong sharks.
• The study, published in Nature Ecology & Evolution, was led by first author Lipin Diao with corresponding authors Ryosuke Motani of the University of California, Davis and Da-yong Jiang of Peking University, alongside the Geological Museum of Guizhou.
• Researchers propose that the extensive bony armor reduced water exchange through the skin, while internal gills may have removed excess salt, though salt regulation and reproduction remain hypotheses since soft tissues were not preserved.