An artist's impression of an Entelognathus - an armoured fish. Image obtained on September 24, 2013. AFP: Brian Choo/Chinese Academy of Sciences
A team of scientists, including an Australian, have found a fossil of a 419-million-year-old ancient armoured fish, in what is being hailed as the most significant paleontological discovery in decades.
Hundreds of millions of years ago, fish known as Placoderms had armoured plates and dominated the oceans.
For years, the world's top evolutionary scientists thought Placoderms died out and then somehow modern fish evolved.
Flinders University's Professor John Long say the discovery resolves a major missing link in evolution.
"The unknown question was where did modern fish fauna come from, who was their ancestor?" Professor Long said.
"This ancient fish called Entelognathus is the missing link because it shows that the extinct armoured Placoderms fishes, which dominated the seas, rivers and lakes of the world for 70 million years, actually were the ancestors to all the living fish on the planet today."
At the time of its existence, the fish lived in a warm tropical sea when China was a separate landmass to Asia.
Discovery calls for further researchProfessor Long says the fossil dates to about 50 million years before fish became amphibious.
"This is a huge discovery for science, not just palaeontology," he said.
"This fish fills a gap between an extinct class of animals and the entire living fish fauna on the planet, which is 30,000 species.
"It's a huge discovery that fills a massive gap in our knowledge of the evolution of the first backboned animals."
The Chinese Academy of Science's Professor Zhu, who led the study, says the fossil's jaw looks a lot like those of modern fish.
She says this shows the Placoderm to be the ancestors of modern fish.
"It has a jaw similar to the modern fish, so we can see intermediary between Placoderms and modern fish or modern vertebrae," Professor Zhu said.
As well as in China, significant ancient fossils have also been found in Australia.
Professor Long says the Amadeus Basin, east of Alice Springs, is another place where scientists could unlock the mysteries of evolution.
"We think that the biggest gap in the whole of early vertebrate evolution, down the base of the whole tree, is gap between the jawless fishes and the first jawed fishes like these armoured Placoderms," he said.
"There hasn't been any transition intermediate fossil formed in that space yet found, but the oldest fossil fishes with bone occur right here in central Australia.
"I think a lot more searching needs to be done and we could find the answers to some of these really big questions right here in our own country."
The mainly Chinese research team includes an Australian former PhD student of Professor Long.
The study is published in the journal Nature today.