Fossils of two ancient fish species discovered in China are helping scientists fill a crucial gap in the evolutionary journey from fish to humans, researchers announced on Thursday.

A team from the Institute of Vertebrate Palaeontology and Paleoanthropology under the Chinese Academy of Sciences identified the fossils after more than a decade of fieldwork and laboratory analysis.

The discoveries included the world’s earliest known complete fossil of a primitive bony fish, Eosteus chongqingensis, found in Chongqing.

Researchers also conducted a detailed analysis of the head and teeth of Megamastax amblyodus, the largest known vertebrate from the Silurian Period, unearthed in Qujing.

The findings were published on Thursday in the journal Nature.

According to Zhu Min, an academician with the Chinese Academy of Sciences, bony fishes represent the central branch of the vertebrate family tree.

Their two major lineages, ray-finned fishes and lobe-finned fishes, eventually diversified widely, with one lobe-finned lineage moving onto land during the Devonian Period and evolving into all four-limbed animals, including humans.

The newly identified Eosteus chongqingensis, which lived about 436 million years ago, measured only about three centimetres long but preserved both its head and tail.

Scientists say it shows a mixture of primitive and advanced features, indicating that the defining traits of bony fishes appeared roughly 10 million years earlier than previously believed.

Meanwhile, Megamastax amblyodus, dating to about 423 million years ago, grew to more than one metre in length, making it the largest known vertebrate of its time.

Using advanced imaging and computer-based 3D reconstruction, researchers revealed its full head structure and distinctive double rows of teeth lined with sharp spines.

Researchers said that the fossils belong to the early evolutionary branch of bony fishes that existed before the split between ray-finned and lobe-finned species.

The discoveries helped clarify how early vertebrate jaws and teeth evolved and illuminate the ancestral form that eventually gave rise to modern fishes, land animals and humans.

“These fossils represent a critical stage in the evolutionary pathway from fish to human.

“They show that bony fishes had already diversified at the time, laying the foundation for vertebrates to later move onto land and flourish on Earth,” Mr Zhu said. 
(Xinhua/NAN)