An international team of scientists in China has discovered what may be the earliest known creature with a distinct face, a 419 million-year-old fish that could be a missing link in the development of vertebrates.

The fossil find in China's Xiaoxiang Reservoir, reported in the journal Nature on Thursday, is the most primitive vertebrate discovered with a modern jaw, including a dentary bone found in humans.

"(This) finally solves an age-old problem about the origin of modern fishes," said John Long, a professor in palaeontology at Flinders University in Adelaide.

'We now know that ancient armored placoderms gave rise to the modern fish fauna as we know it.'- John Long, Flinders University in Adelaide

Scientists were surprised to find that the heavily armoured fish, Entelognathus primordialis, a previously unknown member of the now extinct placoderm family, had a complex small skull and jaw bones.

That appeared to disprove earlier theories that modern vertebrates with bony skeletons, called osteichthyes, had evolved from a shark-like creature with a frame made of cartilage.

Instead, the new find provides a missing branch on the evolutionary tree, predating that shark-like creature and showing that a bony skeleton was the prototype for both bony and cartilaginous vertebrates.

"We now know that ancient armored placoderms gave rise to the modern fish fauna as we know it," said Long, who was not part of the team in China.

Long described the discovery as "the most exciting news in palaeontology since Archaeopteryx or Lucy," referring to two fossil discoveries that are crucial to our understanding of the evolution of birds and humans.