A fossil fish discovered in the West Australian Kimberley has been identified as the missing clue in vertebrate evolution, rewriting a century-old theory on how the first land animals evolved.

Monash University PhD students Mr Erich Fitzgerald and Mr Tim Holland were part of the research team, led by Museum Victoria's Head of Science Dr John Long, that made the spectacular discovery by studying a 380 million-year-old fossil fish called Gogonasus, or Gogo fish, named after Gogo Station in Western Australia where it was found.

The fossil skeleton shows the fish's skull had large holes for breathing through the top of the head but importantly also had muscular front fins with a well-formed humerus, ulna and radius the same bones are found in the human arm.

"This new fossil proves that features of land-living tetrapods (four-legged vertebrates) evolved much earlier in their evolutionary history than previously thought," Mr Fitzgerald, a researcher in the School of Geosciences, said. "This means that humans can trace their evolutionary roots, and adaptations for life on land, further back in time, to more than 380 million years ago.

"This little fossil fish, Gogonasus, is therefore the ultimate 'Mother' of all tetrapods."

The research findings are published today in the journal Nature.

"Gogonasus is the new pivotal fossil for understanding the earliest phase in the transition from sea-going fish to land-dwelling tetrapods - from dinosaurs, to kangaroos, and ultimately, us humans,'' Mr Fitzgerald said.

"The fossils of Gogonasus raise the possibility that tetrapods originated not in the northern hemisphere, as is widely thought, but in Gondwana, the ancient southern super-continent, and more specifically Australia. But further discoveries of fossils in Australia are needed to confirm this."