Armored amphibian fossils show a life far from freshwater

The team therefore compared different forms of strontium in the bones with those in the Triassic ocean. Strontium is an element whose chemical signature can mark the water and food an animal encountered; the fossil match indicated that G. maritimus ate seafood and drank seawater. “That means it lived there,” paleobiologist Ryosuke Motani of the University of California, Davis, said.

Independent paleobiologist Lachlan Hart of the University of New South Wales in Sydney, who was not involved in the study, called the result decisive. “For amphibians, ‘this is the first time that that we have hard evidence that they were actually adapted for long-term life in the sea,’” he said.

Hart and colleagues had previously proposed that a different ancient amphibian might be seafaring, though it probably did not dwell permanently in the ocean. That earlier possibility had remained short of direct chemical evidence.

What made a marine amphibian possible?

Porous skin helps modern amphibians breathe and drink, but it also makes them vulnerable to saltwater, disease and toxins.

G. maritimus and its relatives evolved bony body armor, probably for defense. The plates also would have helped prevent water loss.

Unlike modern amphibians, which typically lose their internal gills after the larval stage, this creature and its close relatives retained a fish-like breathing strategy suitable for life in the depths.

These functions are plausible reconstructions from fossils and comparisons with related animals, not behaviors directly observed in an animal that died 237 million years ago.

The fossils hint that G. maritimus lurked on the seafloor as an ambush predator. Its jaw lifted upward, like a toilet seat, allowing a suction attack on fish and other small creatures.

That hunting behavior remains an anatomical inference, not something the fossils can show in motion.

What does this change for the search for marine amphibians?

The practical change is simple: paleontologists should widen the search. Because amphibians are usually sought in terrestrial and freshwater environments, genuinely marine species may have been missed in ancient seabed deposits.

Motani’s broader point was that amphibians did not follow the familiar salt-adaptation rule seen in mammals, reptiles and birds. The find raises the possibility that other amphibian lineages made similar excursions into the sea.

Only two specimens support the identification, and they do not reveal how many such animals lived or how widespread the adaptation was. The practical answer, then, is narrow but useful: marine amphibian fossils are no longer merely speculative, and future searches should include seabed deposits rather than limiting surveys to terrestrial and freshwater environments.

One such fossil changes the list of possibilities. Two can point the next dig toward the right rocks.