Three isolated vertebrae recovered from lake deposits in Japan have been identified as a previously unknown genus and species of giant salamander. The fossils, dated to roughly 3.5 million years ago in the Upper Pliocene, add concrete detail to the evolutionary record of the Cryptobranchidae family and underscore the steady progress that comes from careful re-examination of existing collections.
The new taxon, named Limnospondylus ajimuensis, takes its genus name from Greek roots meaning lake and vertebra. The species name honours the Ajimu locality in Oita Prefecture where the specimens were unearthed in the late 1990s. Researchers first thought the bones belonged to the living genus Andrias, yet closer study revealed distinct features in the mid-trunk vertebra: centra that are short from front to back and tall top to bottom, prezygapophyses stretched strongly sideways, and bases of those processes that flare out broadly.
Evidence built over decades
The three vertebrae are now housed at the Lake Biwa Museum with accession numbers LBM0142000335 (the holotype mid-trunk vertebra), LBM0142000336 and LBM0142000337. Their formal description appears in a paper titled 'A new genus of giant salamander (Urodela, Cryptobranchidae) from the Pliocene of Japan', published in PeerJ this year.
Masahiro Noda, first author from Kyoto University, said the site stands out. "Ajimu contains the only site in the world where fossils of the giant salamander family and extant genera have both been found. I am delighted that this study has highlighted Japan as a crucial region for understanding their evolutionary history."
The animal is estimated to have reached about 1.1 metres in total length. It lived in freshwater lacustrine settings such as lakes, marshes and wetlands. At the same Ajimu deposits, fossils of Andrias also occur. That overlap makes the location unique worldwide and shows that two cryptobranchid genera with contrasting ecological preferences coexisted in East Asia at that time: Limnospondylus adapted to still waters, Andrias to flowing streams.
The discovery illustrates how patient work on old collections can still rewrite parts of the amphibian family tree.
The extinction of Limnospondylus ajimuensis may trace to climatic cooling and the habitat shifts that followed as the Pliocene gave way to the Pleistocene. Such transitions remind observers that species and ecosystems have always responded to large-scale natural change rather than remaining fixed.
