Scientists have identified a previously unknown giant salamander species from fossil bones discovered nearly 30 years ago in Japan. The ancient amphibian, named Limnospondylus ajimuensis, lived around 3.5 million years ago in freshwater lakes and measured about 3.6 feet (1.1 metres) long—almost as large as some of the biggest living amphibians today. The discovery, made by researchers from Kyoto University, sheds new light on the evolution of giant salamanders in Asia.
3.5-Million-Year-Old Fossils Were Found Nearly Three Decades Ago
The discovery is based on three fossilised vertebrae unearthed between 1995 and 1997 in the Tsubusugawa Formation in Japan’s Ajimu region. The fossils remained unidentified for decades before scientists conducted a fresh analysis. The fossil-rich site contains ancient lake sediments that have also preserved the remains of prehistoric elephants, crocodiles and several other extinct animals, making it one of Japan’s most significant paleontological locations.
Why Scientists Initially Misidentified the Fossils
When the fossils were first examined, researchers temporarily classified them under the genus Andrias, which includes the modern Japanese and Chinese giant salamanders. However, the limited fossil material prevented a conclusive identification. Using a much larger collection of fossil and living giant salamander specimens, the Kyoto University research team re-examined the bones and found they belonged to an entirely different evolutionary lineage.
Unique Vertebra Led to the Discovery of a New Species
Scientists determined that the three vertebrae came from different salamanders because they were found at separate locations and varied in size. The fossils included an anterior trunk vertebra, a mid-trunk vertebra and a sacro-caudal vertebra. The breakthrough came when researchers discovered that the mid-trunk vertebra had an anatomical feature never previously seen in any member of the Cryptobranchidae family. This unique characteristic led scientists to establish a completely new genus and species—Limnospondylus ajimuensis.
Discovery Fills a 20-Million-Year Gap in Asia’s Fossil Record
According to first author Masahiro Noda, Ajimu is the only known site in the world where fossils of giant salamanders and their living relatives have both been discovered. Researchers said the finding helps bridge a major gap in the evolutionary history of giant salamanders, whose lineage stretches back nearly 60 million years. Until now, Asia’s fossil record contained a gap of more than 20 million years, leaving scientists with limited evidence of how these amphibians evolved across the region.
What the Discovery Means for Giant Salamander Evolution
The discovery suggests that giant salamanders were once far more diverse across Asia than previously believed. Researchers say Limnospondylus ajimuensis provides crucial evidence that multiple giant salamander lineages coexisted in prehistoric ecosystems before many eventually disappeared. The findings offer valuable insights into the ancient biodiversity of East Asia and improve scientists’ understanding of amphibian evolution over millions of years.
