Scientists say a fossilised skeleton from the Devonian period, found in the Kimberley region of Western Australia, is from a fish that had fins strong enough to support its own body weight.
It also has large holes in its skull for breathing.
It's the first complete and perfect skeleton of the types of fish that gave rise to the first land animals.
The discovery means that fish developed the characteristics of land animals earlier than previously thought and backs up a theory that evolution from water to land occurred earlier in the southern hemisphere, than the north.
The fossil has gone on display at Museum Victoria.