Three fossilized vertebrae sat in a Japanese collection for more than two decades before scientists realized they belonged to a giant salamander species that no one had ever described. The bones, discovered in the late 1990s in Oita prefecture on the island of Kyushu, have now been identified as a new genus and species of giant salamander that lived roughly 3.5 million years ago.
A Salamander Unlike Any Known Species
Researchers at Kyoto University reexamined the fossils and compared them with skeletons from living giant salamanders. The mid trunk vertebra contained anatomical features that do not appear in any other known member of the Cryptobranchidae family. That difference led the team to conclude the fossils represented both a previously unknown species and a new genus. They named it Limnospondylus ajimuensis, combining Greek words for lake and vertebra with a reference to the Ajimu region where the bones were found.
A Meter Long Giant of Ancient Kyushu
The fossils were preserved in the Tsubusugawa Formation, a layer of ancient lake sediments from the Pliocene epoch. Other fossils found in the same formation include elephants and crocodiles, animals no longer native to Japan. Together, these remains point to a period when Kyushu was warmer and more humid than it is today. Limnospondylus ajimuensis lived in broad freshwater lakes and marshes and may have reached about 1.1 meters in length as an adult.
Only five genera in the Cryptobranchidae family had been described before this discovery. The recognition of another genus adds to scientists' understanding of giant salamander diversity. The Ajimu site is the only place in the world where fossils of the giant salamander family and living genera have both been found, according to the research team. The discovery suggests that many more unknown giant salamanders could be hiding among fossils that were previously given the wrong classification.
