In the late 1990s in the Ajimu region of Japan's Oita Prefecture, researchers discovered three fossilized vertebrae belonging to the Cryptobranchidae family of giant salamanders. These were embedded in the Tsubusugawa Formation, Pliocene-era strata of lake deposits dating back approximately 3.5 million years. The strata have also yielded fossils of animals that no longer roam Japan, such as elephants and crocodiles, revealing a glimpse of an era much warmer and more humid than Japan's current climate.