An Amphibian at Sea: Gerrothorax maritimus

ADDED OCTOBER 26, 2026 • STUDY PUBLISHED OCTOBER 26, 2026

The finding

Diao and colleagues describe two nearly complete skeletons from China’s Guizhou Province, dating to about 237 million years ago. Their study identifies Gerrothorax maritimus as the first known fully marine stem amphibian: an extinct relative outside the living amphibian crown group. It was not a modern frog or salamander.

Original study: Nature Ecology & Evolution →

Why infer an ocean lifestyle?

The argument combines articulated skeletons preserved in marine deposits far from land with a strontium isotope record consistent with seawater. Together, these clues support marine residence more strongly than a fossil’s presence in marine rock alone.

A flattened, armored animal

UC Davis describes a broad, flattened body with extensive bony armor. The researchers interpret the skull and body as suited to bottom-dwelling suction feeding: waiting near the seabed and drawing prey into the mouth. Feeding behavior is reconstructed from anatomy, not directly observed.

How could it tolerate salt?

Living amphibians face difficulties maintaining water and salt balance in seawater. The team proposes that armor reduced exchange through the skin, while gills and digestive uptake supported a more fish-like strategy. The exact physiological mechanism remains a hypothesis; fossils do not directly demonstrate salt transport.

What “first” means

This is the researchers’ claim about the known fossil record, not proof that no other amphibian ever lived at sea. Additional discoveries could extend or revise that record. The claim also concerns full marine independence, beyond occasional saltwater tolerance.

Sources and further exploration

• Diao, L., Motani, R., Jiang, D.-Y., Hao, J. & Wang, S. (2026). A fully marine stem amphibian from the Late Triassic of China. Nature Ecology & Evolution. DOI: 10.1038/s41559-026-03209-9.
• UC Davis research announcement, with fossil photographs and reconstruction. October 26, 2026. The university labels its reconstruction as partly AI-assisted.

This explainer draws on the indexed study abstract and the university’s research announcement; the complete journal article was not accessible during preparation.