3.5-million-year-old mystery creature found in Japan is a 'giant' never seen before

Three bones discovered between 1995 and 1997 in the Ajimu region of Japan belong to a giant salamander that scientists had never identified before. The mystery creature has been named Limnospondylus ajimuensis and lived about 3.5 million years ago in lakes. Researchers said that it measured about 3.6 feet, almost as big as some of the largest amphibians we have on Earth today. The three fossilised vertebrae were discovered nearly 30 years ago in the Tsubusugawa Formation. This region has ancient lake sediments which have previously revealed other animals, such as elephants and crocodiles, in the past. Some of the creatures found here no longer exist in Japan.

The salamander bones were initially assigned to the genus Andrias, which includes the Japanese and Chinese giant salamanders. It was only a temporary classification, as scientists did not have enough skeletal material to classify it. A team of researchers from Kyoto University decided to carry out a detailed analysis of the three bones. They used a much broader collection of modern and extinct giant salamander specimens for the study.

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Giant salamander fossils in Japan

Scientists said that since the bones were found in different locations and differed in size, they were not from one animal. The fossils represented an anterior trunk vertebra, a mid-trunk vertebra, and a sacro-caudal vertebra. The revelation happened because of a mid-trunk vertebra. The feature had not been seen in the anatomy of any known member of the giant salamander family, Cryptobranchidae. This led the researchers to create an entirely new species.

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“Ajimu contains the only site in the world where fossils of the giant salamander family and extant genera have both been found,” first author Masahiro Noda said. The team says that the discovery fills a major gap in the history of giant salamanders. The ancient amphibian lineage has been around for roughly 60 million years.

The creatures inhabited much of the Northern Hemisphere, but in Asia, their fossil record has a gap of more than 20 million years. The discovery of Limnospondylus suggests that giant salamanders were once more diverse in Asia than previously believed.