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Wednesday, 28 February, 2001, 23:41 GMT
Fossil fish in Chinese tale
Fish Yu
Fossil fish: Implications for the evolution of land vertebrates
By BBC News Online's Helen Briggs

Ancestors of the first fish that crawled on to land, giving rise to back-boned land animals and eventually humans, probably arose in China, scientists said on Wednesday.

The discovery of a 400-million-year-old fossil fish at a site in what is now southern China throws light on a fishy "garden of Eden", where creatures first evolved lobe-like fins that went on to form limbs.

The fossil fish, which lived near what was once an isolated continent, now Yunnan province, is much more primitive than expected, showing shark-like features.

It could force a reassessment of the evolution of prehistoric fishes, which scientists believe are the common ancestors of all land vertebrates.

An international team in the UK, China and United States carried out the work, which is published in the scientific journal Nature.

Living fossil

Co-researcher Xiaobo Yu of Kean University, New Jersey, US, said the 400-million-year-old fossil specimen, called Achoania, represented a previously unknown form of very early lobe-finned fish.

"Most members of this group are extinct," he told BBC News Online, "except for the living lungfish and the living coelacanth.

"Among the extinct members of the lobe-finned fishes, one branch later gave rise to the earliest tetrapod (also known as land vertebrates, such as amphibians, reptiles, birds, and mammals, including human beings).

"This is why people are very interested to find out how lobe-finned fish arose in the first place."

He said the fossil fish was much more primitive than expected, sharing some features with sharks. "From a layperson's perspective, Achonia suggests that we are more primitive than we used to believe," Dr Yu said.

Distant relative

Palaeontologists believe that the 400-million-year-old fossil is a very distant ancestor of both modern bony fish and lobe-finned fish, now largely extinct.

But the fossil shares some features with the shark family, more primitive fish that are made up of cartilage not bone. Its eyeballs, for example, were anchored in their sockets by strips of connective tissue. Similar features are seen in sharks but not in modern bony fishes such as cod and herring.

"We're finding that alongside the characteristics that we would have expected it to have, it's turning out to have a collection of bizarre, primitive features only seen in other vertebrate groups," said Per Ahlberg of London's Natural History Museum, who collaborated on the study.

Professor Ahlberg said that fossil fish of a similar age to the Chinese fossil had been found in Europe and North America but not lobe-finned ones.

"It's turning out now that an awful lot of the very earliest and most primitive lobe-finned fishes came from China," he told BBC News Online. "Possibly, the beginning of this family tree that eventually led to us came from southern China."

Professor Ahlberg said a number of other fish fossils had been found at the same site, which had never been seen before. The specimens, which are now being examined by scientists, could raise further tantalising clues about the ancestry of land vertebrates.

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