In the late 1990s, scientists working in the Ajimu area of Oita Prefecture, Japan uncovered three fossilized vertebrae from a giant salamander. Cryptobranchidae Family. The bones were preserved in the Tsubusugawa Formation, a layer of ancient lake sediments dating to the Pliocene period, about 3.5 million years ago.
Other fossils found in the same formation include elephants and crocodiles, animals no longer native to Japan. Overall, the remains point to a period when the region was significantly warmer and more humid than today.
At first, researchers placed the Ajimu fossils in the genus andreasWhich includes the largest amphibians alive today. However, scientists lacked sufficient comparative material and anatomical research to determine what type of giant salamander the bones represented.
More than 20 years later, a research team from Kyoto University has returned to the fossils and uncovered new details about their identity.
a salamander unlike any known species
Researchers compare Ajimu bones with living skeletons Cryptobranchidae species. Their analysis revealed that the fossils consisted of an anterior trunk vertebra, a mid-trunk vertebra, and a sacro-caudal vertebra.
The middle trunk vertebra was particularly important because it contained anatomical features that do not appear in any other known member of the giant salamander family. Based on those differences, the team concluded that the fossils belonged to both a previously unknown species and a new genus.
“Ajimu is the only site in the world where fossils of both the giant salamander family and extant genera have been found,” says first author Masahiro Noda. “I’m pleased that this study highlights Japan as an important region for understanding their evolutionary history.”
One meter tall giant of ancient Kyushu
Researchers named the species Limnospondylus ajimuensis. This name combines the Greek words Limemeaning lake, and spondyloswhich means vertebra, while ajimuensis Refers to Ajimu.
This giant salamander lived in the extensive freshwater lakes and swamps that covered parts of Kyushu several million years ago. As an adult, it can reach approximately 1.1 meters in length.
Only five species in Cryptobranchidae The family has already been described, making the identification of another genus an important contribution to scientists’ understanding of giant salamander diversity.
Cryptobranchidae Fossils have been discovered throughout the Northern Hemisphere. However, due to limited anatomical knowledge many specimens have been assigned to the living genus. andreas. The new findings raise the possibility that some of those fossils may actually represent multiple species that have yet to be identified.
Climate change and extinction
Cooler temperatures during the transition from the Pliocene to the Early Pleistocene, as well as major changes in local habitats, likely contributed to the extinction. Limnospondylus ajimuensis.
his relative, andreas japonicusThe Japanese giant salamander, still survives in rivers in the Ajimu area and elsewhere in Japan.
“Recently, giant salamanders native to Japan have faced challenges such as hybridization with exotic species and habitat destruction,” says Noda. “This research has given me a renewed appreciation for the importance of preserving existing species for the future.”