In Late Triassic deposits of Guizhou Province, Chinese and international paleontologists have discovered nearly complete skeletons of an unusual creature that apparently became the first known amphibian capable of living its entire life in the open sea. The new species, named Haiyi xuan, lived about 237 million years ago — shortly after the great Permian extinction, when the oceans were gradually recovering their complexity.
The animal had a flat body covered by a thick bony armor, a broad head, and a large mouth with powerful gill arches. Adults retained gills and, judging by their structure, could breathe underwater without rising to the surface. This set of features allowed it to hide in bottom sediments and ambush small fish, like modern carpet sharks.
To prove that Haiyi xuan actually lived in the sea and was not carried there by currents from land, the scientists used strontium isotope analysis of the bones and host rocks. The isotope ratios in the skeletons matched the seawater of that time and differed from the surrounding sediments, indicating a lifetime equilibrium with the ocean. Additional evidence — the integrity of the skeletons and the absence of signs of long-distance transport — confirmed local burial.
The site of the find was at least thirty kilometers from the nearest ancient island, and the same layers contain marine reptiles such as Guizhouichthyosaurus and sea lilies. This makes it possible to imagine the Triassic marine ecosystem as a complex community in which amphibians occupied the niche of bottom-dwelling ambush predators.
The discovery calls into question previous ideas that amphibians never achieved full marine adaptation. It shows how diverse and unexpected the paths of evolution could be after mass extinctions, when life was colonizing new habitats.
Haiyi xuan reminds us that even in the harshest conditions the planet is capable of producing forms of life that we did not expect to see.
