A brand new genus and species of cryptobranchid salamander that lived in lakes in Japan about 3.5 million years in the past has been recognized from three fossil vertebrae, filling a significant hole within the fossil file of one of many world’s oldest amphibian lineages.
Life reconstruction of Limnospondylus ajimuensis. Picture credit score: Kanon Tanaka.
The Cryptobranchidae is a household of large, absolutely aquatic salamanders native to america, Japan and China.
It contains the most important dwelling amphibian worldwide, reaching as much as 1.8 m (6 ft) in whole size.
Two dwelling genera are at present acknowledged: Andrias, comprised of the Japanese giant salamander (Andrias japonicus) and 4 species from China; and Cryptobranchus, represented by the hellbender (Cryptobranchus alleganiensis) in jap North America.
Though the household originated over 60 million years in the past, its fossil file in East Asia is sparse.
The newly-identified cryptobranchid species inhabited freshwater lacustrine environments of what’s now Japan through the Pliocene epoch, round 3.5 million years in the past.
Named Limnospondylus ajimuensis, the amphibian could have reached a complete size of roughly 1.1 m (3.6 ft).
The animal’s three vertebrae have been collected between 1995 and 1997 from sediments of the Tsubusagawa Formation on Japan’s Kyushu Island.
The fossils had lengthy been assigned to the dwelling large salamander genus Andrias.
However after reexamining the bones, Dr. Masahiro Noda and his colleagues from Kyoto College concluded that the specimens belong to a wholly new genus and species.
“The Tsubusagawa Formation has yielded exceptionally considerable vertebrate and invertebrate fossils. This assemblage is known as the Ajimu fauna,” they stated.
“It’s the solely website on this planet the place fossils of the enormous salamander household and dwelling genera have each been discovered.”
The paleontologists analyzed the fossils utilizing micro-computed tomography and in contrast their anatomy with each dwelling species of large salamanders and their fossil relations.
In addition they used geometric morphometric analyses to quantify variations in vertebral form.
The specimens displayed a mix of traits not seen in any beforehand identified large salamander.
The fossils additionally provide clues concerning the setting that after coated western Japan.
Round 3.5 million years in the past, the Ajimu area consisted of in depth freshwater lakes surrounded by wetlands and forests.
The world supported a wealthy subtropical ecosystem that included crocodilians, turtles, rhinoceroses, elephants and various birds and fishes.
Not like dwelling large salamanders, which inhabit fast-flowing rivers, Limnospondylus ajimuensis lived primarily in lake environments, suggesting extinct family members occupied a broader vary of habitats than their trendy relations.
The researchers speculate that climatic cooling starting about 2.6 million years in the past, along with shrinking freshwater habitats brought on by environmental change, could have pushed the lake-dwelling salamander to extinction.
In the meantime, Japan’s dwelling large salamander, already tailored to river methods, could have been higher geared up to outlive these altering circumstances.
“Just lately, Japan’s native large salamanders have confronted challenges reminiscent of hybridization with international species and habitat destruction,” Dr. Noda stated.
“This analysis has given me a renewed appreciation for the significance of preserving extant species for the long run.”
The workforce’s paper was revealed on-line within the journal PeerJ.
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M. Noda et al. 2026. A brand new genus of large salamander (Urodela, Cryptobranchidae) from the Pliocene of Japan. PeerJ 14: e21362; doi: 10.7717/peerj.21362
