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Marine Amphibian Fossils Reveal First Fully Sea-Living Tetrapod
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Discovery of *Gerrothorax maritimus*
Two nearly complete skeletons of a previously unknown temnospondyl amphibian were recovered from Late Triassic (? 237 million-year-old) strata in Guizhou Province, China. The larger specimen measures about 74 cm in length—roughly the size of a house cat—while the second is slightly smaller at approximately 48 cm. Both fossils exhibit a flattened, heavily armoured body and were found articulated, indicating minimal post-mortem transport. The researchers provisionally named the species *Gerrothorax maritimus*, with the specific epithet meaning “of the sea.”
Geological and Biological Context
During the Late Triassic, the region that is now Guizhou Province formed part of a salty sea. Fossils of fully marine reptiles such as ichthyosaurs occur in the same rock layers, confirming a marine setting. Stem amphibians like *G. maritimus* possessed internal gills and a more complex gut, traits that could have facilitated salt regulation. The extensive dermal armour would have limited water, gas, and salt exchange through the skin, further supporting a marine adaptation.
Evidence Supporting a Marine Lifestyle
Researchers measured strontium isotopic ratios in the bone material; the values match those of contemporaneous seawater, suggesting the animals “grew up drinking the seawater.” The articulated skeletons were discovered at least 30 km from any known landmass of the period, and the lack of transport marks implies the individuals lived and died near the burial site. Together, the anatomical features, geochemical signatures, and depositional context provide converging lines of evidence that *G. maritimus* spent its entire life in the ocean.
Significance for Amphibian Evolution
More than 8,000 modern amphibian species inhabit freshwater or terrestrial habitats, and none are exclusively marine. Amphibian skin is highly permeable, making prolonged exposure to high-salinity water lethal for most extant species. The discovery of a fully marine temnospondyl challenges the view that amphibians never colonised the sea and suggests early lineages experimented with marine niches.
Official Statements & Responses
Steve Brusatte, a palaeontologist at the University of Edinburgh, described the find as a “potentially revolutionary discovery.” Lipin Diao and co-authors emphasized that modern amphibians lack marine representatives largely because of their salt-intolerant skins, a constraint that *G. maritimus* appears to have circumvented. Ryosuke Motani of the University of California, Davis, noted that the species’ armour would have restricted skin-based water and ion exchange, directing physiological reliance toward gills and the gut.
Verbatim Quotes
- “This is potentially a revolutionary discovery,” — Steve Brusatte, University of Edinburgh
- “Mammals, reptiles, and birds all have species that survive without food or freshwater from land; however, amphibians…lack such a member partly because of their salt-intolerant skins,” — Lipin Diao
Data & Statistics
- Age of fossils: ? 237 million years (Late Triassic)
- Specimen lengths: ~ 74 cm and ~ 48 cm
- Modern amphibian diversity: > 8,000 described species, none fully marine
- Number of specimens examined: two nearly complete skeletons
Future Research Directions
The authors plan further isotopic and morphological analyses of additional temnospondyl material from marine deposits to clarify the extent of marine adaptation among early amphibians.