New Giant Salamander Species Identified From 3.5-Million-Year-Old Japan Fossils

Micro-CT Scanning Reveals a Hidden Evolutionary Lineage

For decades, the evolutionary history of giant salamanders remained obscured by a biological paradox: their body plans are remarkably conservative. Because their skeletons have changed so little over millions of years, fossilized remains are often indistinguishable from their modern descendants. As Scitechdaily reported, this led paleontologists to broadly categorize ancient specimens under the existing genus Andrias, which includes the living Japanese and Chinese giant salamanders.

The breakthrough came when a research team from Kyoto University re-examined three fossilized vertebrae originally unearthed by collector Eiichi Kitabayashi between 1995 and 1997 along the Fukami River. As Earth.com detailed, the team utilized micro-computed tomography (micro-CT) to peer inside the fossils. This high-fidelity imaging revealed internal structural traits in the mid-trunk vertebra that were previously invisible to the naked eye.

Anatomy and Lifecycle of Limnospondylus ajimuensis

The name Limnospondylus ajimuensis is derived from the Greek words for “lake” and “vertebra,” honoring the region in Oita Prefecture where the fossils were found. According to Nautil.us, the species likely reached lengths of approximately 1.1 meters (roughly 3.6 feet). Analysis of the growth rings preserved within the largest vertebra suggests that the animal lived for about 17 to 18 years, showing signs of steady, consistent growth throughout its life.

View this post on Instagram about Oita Prefecture

The physical differences noted by the researchers are distinct. The mid-trunk vertebra of L. ajimuensis features a compact profile with broad, heavy bases for the joints and a unique alignment of its lateral wings. Archyde noted that these structural markers indicate a specialized biomechanical load-bearing capacity that differs from the modern Andrias genus, suggesting the ancient creature faced different physical demands in its aquatic environment.

Ancient Kyushu: A Lost Wetland Ecosystem

The discovery provides a window into a Kyushu that looks nothing like the island today. During the Late Pliocene, approximately 3.5 million years ago, the region featured wide, freshwater lakes fringed by marshes and forests. As Plaxuvo reported, the environment was warmer and more humid than the modern era, with annual rainfall exceeding 35 inches. This habitat supported a diverse array of species, including rhinos, crocodiles, southern turtles, and Stegodon elephants.

This lifestyle contrast is significant. While modern giant salamanders are famously adapted to flowing, high-oxygen river systems, L. ajimuensis appears to have been a lake-dwelling specialist. The subsequent cooling of the climate around 2.6 million years ago, as the Pliocene transitioned into the Pleistocene, likely caused these lakes to shrink, leading to the extinction of this specialized genus.

Conservation Stakes for Modern Salamanders

The researchers emphasize that this discovery is not merely about paleontology; it serves as a reminder of the fragility of current amphibian populations. Japan’s native giant salamanders, Andrias japonicus, currently face severe threats from habitat destruction and hybridization with invasive species, as PlanetSudoku reported.

Scientists believe that many other fossils currently stored in museum collections may also be misidentified. By applying modern imaging technologies like micro-CT scanning to these “legacy” collections, researchers hope to uncover more hidden diversity within the giant salamander family tree, potentially revealing other species that have remained unrecognized for decades.