Fossils of an ancient amphibian discovered in China suggest the species lived its whole life in the ocean, a first for any known amphibian. The specimens, found in marine sediments from the Late Triassic era, challenge the long-held understanding that amphibians cannot survive in saltwater.
An international team led by geologist Lipin Diao has described a new species of ancient amphibian, Gerrothorax maritimus, in the journal Nature Ecology & Evolution. The two fossils were discovered by local farmers in Guanling County, in a rock layer about 237 million years old. The site was completely submerged by sea during the Late Triassic, and the fossils were found alongside marine animals such as ichthyosaurs, crinoids and turtles.
Unlike any modern amphibian, Gerrothorax had a flat body covered in plates of hard armour. The researchers say this armour would have prevented water absorption through the skin, forcing the animal to drink and absorb water through its digestive tract, a key adaptation to marine life.
Both skeletons were found more than 30 kilometres from any possible nearby islands and were almost fully intact, with limbs and even fingers preserved. This suggests the animals died where they lived, rather than drifting out to sea after death. “Carcasses at sea, unless they sink to the bottom right away, tend to dry out and lose limbs prior to sinking to the bottom,” said co-author Ryosuke Motani, a palaeontologist at the University of California, Davis. “But these animals had their fingers preserved, so that means they probably died near where they lived.”
Further evidence came from strontium isotope analysis of the bones. The ratio of strontium isotopes in the fossils matched Triassic seawater rather than the surrounding rock, indicating the animals grew up drinking seawater.
The more complete specimen measures at least 73.7 centimetres along its preserved midline. Motani described it as “really chunky”, comparable in body mass to a giant salamander but much broader. Its flat shape, weak limbs and heavy armour would have made moving on land difficult, if it ever returned there.
The discovery suggests that some ancient amphibians evolved to live permanently in the sea, overturning assumptions about the group’s habitat limitations.
Analysis
Why This Matters
- The finding challenges the core biological assumption that amphibians cannot live in saltwater, opening new questions about amphibian evolution and adaptation.
- It provides the first clear fossil evidence of a fully marine amphibian, filling a gap in the understanding of how tetrapods returned to the sea.
- The discovery may prompt re-examination of other fossil sites for marine amphibians previously overlooked because they were thought impossible.
Background
Modern amphibians rely on porous skin for gas and water exchange, which generally makes saltwater environments uninhabitable for them. This fossil from the Late Triassic, around 237 million years ago, shows that some ancient amphibians evolved physical adaptations, such as heavy body armour, to survive in marine conditions. The discovery was made in the Guizhou Triassic Fossil Sites in China, a region known for marine reptile fossils.
What to Watch
- Whether re-examination of other temnospondyl fossils from marine deposits reveals additional marine-adapted species.
- Further studies on the physiological adaptations of G. maritimus, particularly how it managed water balance and salt excretion.
- The potential for new fossil finds in the Guizhou Triassic Fossil Sites to shed more light on the ecosystem this amphibian inhabited.
Checked
12 claims in this story checked against 1 source: 8 supported.
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- SupportedThe fossils suggest Gerrothorax lived its entire life at sea.ScienceAlert: “But two fossils unearthed from a Late Triassic deposit in China suggest an ancient amphibian species not only inhabited saltwater – it made a proper return to the ocean, living its whole life at sea.”
- SupportedTwo specimens found in China offer first evidence of a marine amphibian.ScienceAlert: “An Armored Amphibian That Lived Its Whole Life at Sea? It's a Fossil First.”
- SupportedMotani said: “Carcasses at sea, unless they sink to the bottom right away, tend to dry out and lose limbs prior to sinking to the bottom,”ScienceAlert: ““Carcasses at sea, unless they sink to the bottom right away, tend to dry out and lose limbs prior to sinking to the bottom,” Motani adds .”
- SupportedMotani said: “But these animals had their fingers preserved, so that means they probably died near where they lived.”ScienceAlert: ““But these animals had their fingers preserved, so that means they probably died near where they lived.””
- Partly supportedMotani called the animal “really chunky” and said it was comparable in body mass to a giant salamander but much broader.ScienceAlert: ““It's probably, body mass-wise, about the same as the giant salamander, but what's different is that giant salamanders are elongated whereas this animal is really chunky,” says Motani.”
- Partly supportedAn international team led by geologist Lipin Diao described the new species in Nature Ecology & Evolution.ScienceAlert: “Geologist Lipin Diao and colleagues present the strange new amphibian, Gerrothorax maritimus, in the journal Nature Ecology & Evolution .”
- SupportedLocal farmers found the fossils in Guanling County, in a rock layer about 237 million years old.ScienceAlert: “The two fossils were discovered by local farmers in Guanling County, in a layer of rock about 237 million years old”
- SupportedBoth specimens were found more than 30 kilometres from any possible nearby islands.ScienceAlert: “Both specimens were found more than 30 km [18.6 miles] from any possible nearby islands”
- Partly supportedStrontium isotope ratios in the bones matched Triassic seawater rather than the surrounding rock, indicating the animals grew up drinking seawater.ScienceAlert: “The strontium in these bones matched Triassic seawater, not the rock they were buried in. “It is most likely that the two [ Gerrothorax ] individuals that gave rise to the type specimens grew up drinking the seawater”
- SupportedThe more complete specimen measures at least 73.7 centimetres along its preserved midline.ScienceAlert: “The more complete specimen of the two fossils measures at least 73.7 cm (2.4 feet) along its preserved midline”
- Partly supportedThe discovery challenges the long-held understanding that amphibians cannot survive in saltwater.ScienceAlert: “No amphibian on Earth lives in the ocean. Their porous skin – crucial for gas and water exchange – generally can't cope with the salt.”
- SupportedThe researchers say the armour prevented water absorption through the skin, requiring the animal to drink and absorb water through its digestive tract.ScienceAlert: “the body armor of Gerrothorax prevented water absorption through the skin, mandating water drinking and absorption from the digestive tract unlike in most extant amphibians”
