China Focus: Scientists unlock mystery of 400-million-year-old fish

BEIJING, May 9 (Xinhua) -- A team of Chinese and Australian researchers has for the first time discovered fossils of Palaeospondylus in an area located outside Scotland, according to the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences.

Dating the fossils to approximately 400 million years ago, the research team has pushed the chronological record of this species back by about 10 million years. Using CT scanning and 3D reconstruction, the team fully restored the neurocranial structures of Palaeospondylus, providing critical evidence for unraveling its evolutionary position. Palaeospondylus was a small, enigmatic early vertebrate.

The study, published as a cover article in the academic journal National Science Review, was highlighted in an accompanying commentary. "They make progress with interpreting its anatomy, and are able to disprove some previous hypotheses about its relationships," and the interpretation "represents a huge improvement on our previous understanding," the commentary noted.

First documented in 1890, this tiny, eel-like fish measuring just a few centimeters, has long baffled scientists. Over 1,000 specimens from Scotland revealed skeletal features starkly different from other fish.

For over a century, researchers variously classified it into nearly every major fish group, from jawless hagfish to lobe-finned fish larvae, and yet its phylogenetic position remained unresolved, earning it the title of "one of the most mysterious early vertebrates."

The newly discovered fossils, named Palaeospondylus australis, were found in Cravens Peak Beds, Georgina Basin, western Queensland, Australia, within Early Devonian Emsian epoch strata, believed to be roughly 400 million years old. These fossils coexisted with jawless fish, armored placoderms, early sharks, spiny fish and diverse bony fish.

Scientists revealed three-dimensionally preserved brain structures and mineralized tissues via these fragmentary fossils. High-resolution CT scans and 3D techniques allowed the team to reconstruct the complete brain cavity, including semicircular canals and nerve canals, which are key morphological evidence for determining its evolutionary lineage, said Lu Jing, leader of the research team.

Phylogenetic analysis based on this data suggests Palaeospondylus likely belongs to the cartilaginous fish lineage rather than the tetrapod stem group as previously hypothesized, said Lu with the IVPP.

Also, the team developed a novel cross-platform volumetric data reconstruction method, enabling efficient restoration and cross-verification. This technique significantly enhances the processing and visualization of paleontological CT data, paving the way for more in-depth morphological analyses and shared validation workflows, and is expected to play a transformative role in future research, Lu said. ■