The discovery of what may be the earliest known creature with a face has provided scientists with the missing link needed to solve an age-old mystery as to when vertebrates developed jaws.

Discovered in China, the fossilised fish preserved in three-dimensions is the most primitive vertebrate found with a modern type of jaw, including a dentary bone found in humans.

The 419-million-year-old fish from the placoderm family had a complex lower jaw structure..

A previously unknown member of the now extinct placoderm family, the ancient fish would have been largely covered by armoured plates. But it is the complex lower jaw structure of the 419-million-year-old fish that has scientists so exhilarated.

''It is very exciting news and I don't use superlatives like that very often,'' said Flinders University strategic professor in palaeontology John Long. ''This fish is pivotal in understanding the very first creatures to have jaws.''