A new genus and species of cryptobranchid salamander that lived in lakes in Japan about 3.5 million years ago has been identified from three fossil vertebrae, filling a major gap in the fossil record of one of the world’s oldest amphibian lineages.
Life reconstruction of Limnospondylus ajimuensis. Image credit: Kanon Tanaka.
The Cryptobranchidae is a family of giant, fully aquatic salamanders native to the United States, Japan and China.
It includes the largest living amphibian worldwide, reaching up to 1.8 m (6 feet) in total length.
Two living genera are currently recognized: Andrias, comprised of the Japanese giant salamander (Andrias japonicus) and four species from China; and Cryptobranchus, represented by the hellbender (Cryptobranchus alleganiensis) in eastern North America.
Although the family originated over 60 million years ago, its fossil record in East Asia is sparse.
The newly-identified cryptobranchid species inhabited freshwater lacustrine environments of what is now Japan during the Pliocene epoch, around 3.5 million years ago.
Named Limnospondylus ajimuensis, the amphibian may have reached a total length of approximately 1.1 m (3.6 feet).
The animal’s three vertebrae were collected between 1995 and 1997 from sediments of the Tsubusagawa Formation on Japan’s Kyushu Island.
The fossils had long been assigned to the living giant salamander genus Andrias.
But after reexamining the bones, Dr. Masahiro Noda and his colleagues from Kyoto University concluded that the specimens belong to an entirely new genus and species.
“The Tsubusagawa Formation has yielded exceptionally abundant vertebrate and invertebrate fossils. This assemblage is referred to as the Ajimu fauna,” they said.
“It is the only site in the world where fossils of the giant salamander family and living genera have both been found.”
The paleontologists analyzed the fossils using micro-computed tomography and compared their anatomy with both living species of giant salamanders and their fossil relatives.
They also used geometric morphometric analyses to quantify differences in vertebral shape.
The specimens displayed a combination of traits not seen in any previously known giant salamander.
The fossils also offer clues about the environment that once covered western Japan.
Around 3.5 million years ago, the Ajimu region consisted of extensive freshwater lakes surrounded by wetlands and forests.
The area supported a rich subtropical ecosystem that included crocodilians, turtles, rhinoceroses, elephants and diverse birds and fishes.
Unlike living giant salamanders, which inhabit fast-flowing rivers, Limnospondylus ajimuensis lived primarily in lake environments, suggesting extinct members of the family occupied a broader range of habitats than their modern relatives.
The researchers speculate that climatic cooling beginning about 2.6 million years ago, together with shrinking freshwater habitats caused by environmental change, may have driven the lake-dwelling salamander to extinction.
Meanwhile, Japan’s living giant salamander, already adapted to river systems, may have been better equipped to survive those changing conditions.
“Recently, Japan’s native giant salamanders have faced challenges such as hybridization with foreign species and habitat destruction,” Dr. Noda said.
“This research has given me a renewed appreciation for the importance of preserving extant species for the future.”
The team’s paper was published online in the journal PeerJ.
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M. Noda et al. 2026. A new genus of giant salamander (Urodela, Cryptobranchidae) from the Pliocene of Japan. PeerJ 14: e21362; doi: 10.7717/peerj.21362
