Image copyright Giles Hamm Image caption The scientists think the shelter, 550km north of Adelaide, was used episodically over thousands of years

The speed at which the first Aboriginal settlers spread across Australia has been underlined by the discovery of an ancient rock shelter north of Adelaide.

The rock fissure in the Flinders Ranges contains tools and other artefacts that date back to around 49,000 years ago.

That means Aboriginal people must have colonised large parts of the continent within a few millennia of their arrival.

Details of the Warratyi shelter are reported in the journal Nature.

"It is the southernmost oldest site in the continent (there is another site in southwestern Australia called Devil’s Lair, which is quite old), but in terms of inland occupation, it’s significant geographically because it shows people are moving very quickly around the continent and into the interior part of the continent," lead scientist Giles Hamm told BBC News.

The next oldest settlement in Australia’s arid outback region is 10,000 years younger - hence the excitement in the Warratyi find.

"To our people, it’s not really a surprise," commented Clifford Coulthard from the Adnyamathanha Traditional Lands Association.

"A lot of the old people said we were here a long time ago. We’re all happy about it."

It was Mr Coulthard who actually found the shelter while working alongside Mr Hamm.

Image copyright Peter Murray Image caption Diprotodon was the size of a hippo - the biggest marsupial that ever lived

Dating of the sediments and objects in the cave, which include not just tools, but animal bones, charcoal, ash, egg shells and plant material, reveal that humans were using the site in sporadic fashion over thousands of years. The research team sees periods of frequent use interspersed with what may have been times of abandonment.

But what was left on the ground is certainly a boon now to those trying to piece together the chronology and scope of Aboriginal settlement, which likely started in the northwest of the continent more than 50,000 years ago.

Among the finds are examples of the oldest bone and stone tools in Australia.

They push back significantly the dates for the development and use of some of these key technologies.

Image copyright Giles Hamm Image caption This sharpened bone point, dated to be 38,000-40,000 years old, is now the oldest bone tool yet found in Australia

Also in the cave is a bone specimen from the biggest marsupial that ever lived, the wombat-like creature Diprotodon optatum, and egg shells from the huge flightless bird Genyornis newtoni.

The presence of these remains suggests strongly that Warratyi's ancient residents were hunting the local megafauna.

There has been a big controversy in Australian science for many years about what drove the continent's peculiar and iconic mix of big beasts to extinction, with some arguing for a human-hunting cause and others pointing to the disrupting impacts of climate change.

But team-member Prof Gavin Prideaux said Australia's earliest settlers were clearly involved.

"None of us can imagine a way a Diprotodon could have scaled the cliff up to that cave," he told reporters. "It had to have been brought there by people. More than likely they were eating Diprotodon."

Researchers trying to understand the culture of these early people will be interested in the discovery of red ochre - a pigment that would have had ceremonial use, just as it does with today's indigenous people.

Image copyright Lee Arnold Image caption The team has placed great emphasis on accurate dating

The ochre unearthed at Warratyi was determined to be between 49,000 and 46,000 years old.

The material is alien to the locality where Precambrian rocks dominate. The ochre must have been imported, therefore.

Another team-member, Dr Lee Arnold, said the importance of Warratyi was cemented by its very secure dating - something that has proved difficult, and controversial, at other archaeological sites across Australia.

"At a lot of sites, there's not been the preservation of materials that are needed to use widely applicable techniques such as radiocarbon dating. Bone is usually quite degraded in arid environments," he explained.

"Charcoal, which is also used in radiocarbon dating, can move quite readily through certain sedimentary environments and can have contaminants. And also, a lot of these sites are quite close to the limit of radiocarbon dating."

The Warratyi study used additionally the technique known as optically stimulated luminescence dating, and targeted various types of materials at different depths in the shelter's floor sediments.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos