What is believed to be the oldest vertebrate fossil on Earth has been discovered in South Australia's Flinders Ranges.

ABC's PM reports that palaeontologists from the South Australian Museum were last night en route to the remote site deep in the north of the state to further authenticate the discovery, which could pre-date the previously oldest fossil found in China by 30 million years.

Our very most distant relative looks like a long tadpole, about 65 centimetres long., with muscles, a head, a fin on its back, but most importantly, a backbone, says PM's Nance Haxton.

Dated to be at least 560 million years old, the fossil could be the elusive Holy Grail that shows the first ancestors of the human race.

South Australian Museum Director, Dr Tim Flannery, says the discovery is of enormous significance.

'Well, it's not so much humans, it's really the origin of all other things, humans, dogs, birds, fish, everything with a backbone and what it's suggesting is that perhaps this lineage goes back a lot further in time than any of us imagined,' he told PM.

Nilpena station owner Ross Fargher stumbled across the fossil five years ago while driving around his 870 square kilometre cattle property.

For years he had the fossil on display on his veranda along with other discoveries, for the interest of tourists, but had no idea that he had discovered a previously unknown fossil site.

'I knew that it was different from any other fossils here, we do have the Ediacara Fossil Reserve on the northern end of our property, and yeah, I just happened to stumble across this one just on the southern side of the fossil reserve in a sort of rocky outcrop,' he says.

'I pulled up there on a motor bike one day and I was just sort of having a bit of a look around and found a couple of fossils, and then happened to spot this one that was a bit different to the others.'

Dr Tim Flannery says the South Australian Museum will now develop a special fossil gallery to exhibit the unique specimens, and ultimately, a display on site in the Flinders Ranges as well.

The precise location of the discovery is being kept secret to prevent specimens being stolen by international fossil smugglers.