Scientists say an Aboriginal rock art depiction of an extinct giant bird could be Australia's oldest painting.

The red ochre painting, which depicts two emu-like birds with their necks outstretched, could date back to the earliest days of settlement on the continent.

It was rediscovered at the centre of the Arnhem Land plateau about two years ago, but archaeologists first visited the site a fortnight ago.

A palaeontologist has confirmed the animals depicted are the megafauna species Genyornis.

Archaeologist Ben Gunn said the giant birds became extinct more than 40,000 years ago.

"The details on this painting indicate that it was done by someone who knew that animal very well," he said.

He says the detail could not have been passed down through oral storytelling.

"If it is a Genyornis, and it certainly does have all the features of one, it would be the oldest dated visual painting that we've got in Australia," he said.

"Either the painting is 40,000 years old, which is when science thinks Genyornis disappeared, or alternatively the Genyornis lived a lot longer than science has been able to establish."

Mr Gunn says there are paintings of other extinct animals right across the area including the thylacine, or tasmanian tiger, the giant echidna and giant kangaroo.

"It does give you a window back to a time that you can pinpoint, and in the case of the Genyornis it's a very long picture," he said.

The traditional owners of the land in the Northern Territory say they are excited the painting could be Australia's oldest dated rock art.

The Jawoyn Association's Wes Miller says the painting is one of thousands rediscovered across Arnhem Land in recent years.

"It verifies that the Jawoyn people were living in this country for a very, very long time," he said.

"People say it, but once again this is clearly a demonstration of how long Jawoyn people have been in this country and other Indigenous groups. It's great from that point of view. It's pretty exciting stuff."