Kyoto University Team Names Limnospondylus ajimuensis, a New Giant Salamander Genus From 3.5-Million-Year-Old Japanese Fossils
Kyoto University researchers re-examined three 1990s fossils to identify a new genus of giant salamander that lived in Japanese lakes 3.5 million years ago.
Overview
A Kyoto University research team has identified a new genus and species of giant salamander, Limnospondylus ajimuensis, from three fossilized vertebrae that sat unclassified for more than two decades after their discovery in Japan. The specimens, originally collected in the late 1990s in the Ajimu region of Oita prefecture, were long assigned to the living genus Andrias for lack of comparative material, according to Kyoto University’s release on EurekAlert. The findings appeared in the journal PeerJ on 3 June 2026.
What We Know
The three vertebrae — an anterior trunk vertebra, a mid-trunk vertebra, and a sacro-caudal vertebra — were embedded in the Tsubusugawa Formation, Pliocene-era lake-deposit strata dating back approximately 3.5 million years, according to Kyoto University’s release. The same strata have also yielded fossils of elephants and crocodiles, according to the release, pointing to a Japan that was once far warmer and more humid than it is today. Sci.News reports that the broader Ajimu-region ecosystem 3.5 million years ago included crocodilians, turtles, rhinoceroses, elephants, and diverse birds and fishes, set amid extensive freshwater lakes surrounded by wetlands and forests.
After comparing the specimens against the skeletons of living Cryptobranchidae species, researchers found that the mid-trunk vertebra carried unique morphological traits not seen in any other member of the family, leading them to conclude the fossils represent a new species and genus, according to Kyoto University’s release. Sci.News reports the team used micro-computed tomography and geometric morphometric analyses to quantify differences in vertebral shape between the Ajimu fossils and both living and fossil relatives.
The new species was named Limnospondylus ajimuensis, combining the Greek words limne (lake) and spondylos (vertebra) with a reference to the Ajimu site, and researchers estimate the animal reached approximately 1.1 meters in length by adulthood, according to Kyoto University’s release. Unlike living giant salamanders, which favor fast-flowing rivers, Limnospondylus ajimuensis appears to have lived primarily in lake environments, according to Sci.News, suggesting extinct members of the family occupied a broader range of habitats than their modern relatives.
“Ajimu contains the only site in the world where fossils of the giant salamander family and extant genera have both been found,” said Masahiro Noda, the study’s first author and a Kyoto University researcher, according to the release. “I’m delighted that this study has highlighted Japan as a crucial region for understanding their evolutionary history.”
Only five genera of the Cryptobranchidae family had previously been described, according to Kyoto University’s release, and ScienceDaily frames the new find as the family’s sixth genus. The Cryptobranchidae family includes the largest living amphibian in the world, reaching up to 1.8 meters in total length, and currently comprises two living genera: Andrias, made up of the Japanese giant salamander Andrias japonicus and four Chinese species, and Cryptobranchus, represented by the hellbender (Cryptobranchus alleganiensis) of eastern North America, according to Sci.News. Although the family originated more than 60 million years ago, its East Asian fossil record has remained sparse, the outlet reports.
Researchers believe climatic cooling during the transition from the Pliocene to the early Pleistocene, along with related habitat changes, may have contributed to the extinction of Limnospondylus ajimuensis, according to Kyoto University’s release. Sci.News reports that researchers date the onset of that cooling to roughly 2.6 million years ago and suggest that Japan’s living giant salamander, already adapted to river systems, may have been better equipped to survive the shift than its lake-dwelling relative. Andrias japonicus still inhabits rivers in the Ajimu region and elsewhere in Japan today, according to Kyoto University’s release.
The study was funded by Japan’s Science and Technology Agency, the Environmental Restoration and Conservation Agency, and the Fukada Geological Institute, according to the release.
What We Don’t Know
The researchers say fossils belonging to the Cryptobranchidae family have turned up elsewhere across the Northern Hemisphere but have often been classified under the extant genus Andrias for lack of sufficient identifying research, according to Kyoto University’s release; how many of those specimens might likewise belong to unrecognized genera or species remains an open question the study does not resolve. Noda also linked the findings to present-day conservation, telling Kyoto University that “Japan’s native giant salamanders have faced challenges such as hybridization with foreign species and habitat destruction,” adding that “this research has given me a renewed appreciation for the importance of preserving extant species for the future,” according to the release.