A newly discovered genus and species of cryptobranchial salamander, which thrived in Japanese lakes approximately 3.5 million years ago, has been identified from three fossil vertebrae. This finding fills a critical gap in the fossil record of one of the world’s oldest amphibian lineages.

Reconstruction of Limnospondylus ajimuensis. Image credit: Kanon Tanaka

The Cryptodactylidae family includes giant, fully aquatic salamanders found in the United States, Japan, and China.

This family includes the largest living amphibian, which can grow up to 1.8 meters (6 feet) in length.

Currently, two extant genera are recognized: Andrias, which features the Giant salamander (Andrias japonicus) and four species from China; and Cryptobranchus, represented by the Hellbender (Cryptobranchus alleganiensis) endemic to eastern North America.

This family has existed for over 60 million years, yet its fossil record in East Asia remains limited.

The newly identified cryptobranch species, named Limnospondylus ajimuensis, inhabited the freshwater lake ecosystems of modern-day Japan during the Pliocene epoch, around 3.5 million years ago.

This amphibian may have reached an estimated total length of about 1.1 meters (3.6 feet).

Three vertebrae from this creature were excavated from sediments in the Tsubusu River Formation on Kyushu Island, Japan, between 1995 and 1997.

Initially classified within the modern giant salamander genus Andrias, further examination by Dr. Masahiro Noda and his team at Kyoto University revealed that these specimens belonged to a completely new genus and species.

“The Tsubusu Formation hosts an incredibly rich collection of vertebrate and invertebrate fossils, contributing to our understanding of the Ajimu fauna,” they stated.

“This is the only region globally where fossils of both giant salamanders and extant genera have been discovered.”

Paleontologists employed microcomputed tomography to analyze the fossil and compared its anatomy with that of modern giant salamanders and related species.

Geometric morphometric analysis was also utilized to quantify variations in spine shape.

The study revealed a unique combination of characteristics not previously observed in known giant salamanders.

These fossils also offer insights into the environment that once dominated western Japan.

About 3.5 million years ago, the Ajimu region was a vast freshwater lake, bordered by wetlands and forests.

This habitat supported a diverse subtropical ecosystem, including crocodiles, turtles, rhinos, elephants, and numerous bird and fish species.

In contrast to modern giant salamanders that inhabit fast-flowing rivers, Limnospondylus ajimuensis primarily occupied lake environments, indicating that extinct members of this family occupied a broader range of habitats than their modern counterparts.

Researchers hypothesize that a cooling climate beginning around 2.6 million years ago, along with dwindling freshwater habitats due to environmental shifts, may have led to the extinction of lake-dwelling salamanders.

In contrast, Japan’s giant salamander had already adapted to river ecosystems and may have been more resilient in the face of these changing conditions.

“Currently, Japan’s native giant salamander faces threats such as hybridization with non-native species and habitat loss,” notes Dr. Noda.

“This research highlights the critical importance of preserving existing species for future generations.”

The team’s findings were published in an online journal, PeerJ, in their paper.

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Masato Noda et al.. 2026. A new genus of giant salamander from the Pliocene of Japan (Squamata, Epibranchidae). PeerJ 14: e21362; doi: 10.7717/peerj.21362