Scientists have calculated the artwork, slightly smudged after thousands of years in the wilderness, pre-dates European settlement in Australia and could be up to 40,000 years old.
The large painting was discovered on the Arnhem Land plateau in the Northern Territory by members of the Jawoyn Association Aboriginal Corporation during routine patrols of the area about two years ago.
However archaeologists only visited the site for the first time last month.
Archaeologist and rock art specialist Ben Gunn, who assessed the painting of the two large birds with outstretched necks, sent a photograph of the rock art to a local palaeontologist who determined it was a depiction of the megafauna species Genyornis.
The Genyornis – a heavy bird which had a broad, rounded beak and was about twice the size of an emu – became extinct about 40,000 years ago.
If verified, the painting would pre-date rock art from parts of Europe which have been reliably dated to 30,000 years ago.
“Either the painting is 40,000 years old, or the Genyornis lived much longer than we thought,” Mr Gunn told The Times.
He described the image as in good condition but “slightly smudged”, and added that there is too much detail in the image for the birds to have been painted through word of mouth.
“It doesn’t look like it has been repainted,” Mr Gunn said. “For the amount of detail that is on there you are looking at someone who knew what the animal looked like.”
Because of the historical significance of the find, the exact location of the site is being kept secret - Mr Gunn would only divulge that it is accessible only by helicopter in the Arnhem Land region.
Arnhem Land is a large Aboriginal reserve in the remote north-eastern corner of the Northern Territory which is known for its abundance of ancient rock art.
The painting of the Genyornis is part of a larger cluster of indigenous rock art paintings in the region which are currently being assessed by scientists.
According to Mr Gunn it is surrounded by paintings of other extinct animals such as the thylacine, better known as the Tasmanian Tiger, which died out 3,000 years ago; a giant echidna; giant kangaroo; and a Palorchestes, a tapir-like creature which became extinct about 18,000 years ago.
Mr Gunn said the next step for the scientists to determine the species depicted in the image is to excavate the floor of the shelter which houses the Genyornis painting to calculate the age of the rock and equate that with the age of the painting.