Triassic Armored Amphibian Uncovered as a Seafaring Predator

A study published in Nature Ecology & Evolution describes two well‑preserved fossils of Gerrothorax maritimus from the Late Triassic (roughly 237–201 million years ago). Each specimen measured about 70 cm—comparable to the length of a skateboard—and was covered in bony plates. The animals resembled their freshwater relatives, but the fossils were discovered on an ancient seabed about 30 km from any landmass.

To determine whether these creatures lived in the ocean, the research team analyzed strontium isotopes in the fossil bones. The isotopic signatures matched those of Triassic seawater, indicating that G. maritimus fed on marine prey and drank saltwater. “That means it lived there,” said Ryosuke Motani, the lead paleobiologist.

The find provides the first solid evidence that an amphibian was truly adapted for long‑term marine life, according to paleobiologist Lachlan Hart of the University of New South Wales, who was not involved in the study. Previous hypotheses had suggested other ancient amphibians might have been seafarers, but likely not true ocean dwellers.

Marine adaptations are rare among amphibians. The fossil record is rich in marine mammals, reptiles and birds, yet amphibians have long puzzled researchers because their skin is vulnerable to saltwater. “Amphibians were always the problem because they did not really follow the rule,” Motani noted.

G. maritimus overcame these challenges with several key traits. Its bony armor likely served both defensive and water‑retention purposes, reducing desiccation. Unlike modern amphibians, which typically lose internal gills after metamorphosis, this species retained a fish‑like breathing apparatus suited for underwater life.

The fossils also suggest an ambush‑predator lifestyle. The creature’s jaw could lift like a toilet seat, creating suction to capture fish and other small prey.

Because amphibians are usually sought in freshwater and terrestrial deposits, ancient marine environments may have been overlooked. “Because they’re amphibians, we would be looking for them in terrestrial freshwater environments,” Hart said, hinting that more marine amphibians could be uncovered in the future.

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