A rock art painting believed to depict a bird which became extinct 40,000 years ago has been found in northern Australia, raising hopes it could be the oldest rock art painting yet found Down Under.

The painting in red ochre, which shows two tall birds vaguely similar to the emu, was found on a shallow rock shelter two years ago by an Aboriginal group which is documenting rock art sites in Arnhem Land.

Archaeologists who viewed it this month said the figure was more likely to be a giant extinct bird rather than an emu.

"Two weeks ago we went there to record the site. The animal wasn't an emu, it looked like the megafauna bird genyornis, with thick, huge toes and short legs," remarked archaeologist Ben Gunn.

"We showed it to a paleontologist who answered that it presented all the characteristics of the genyornis.

"It means either that it was painted at the time of the genyornis bird, or that the genyornis had lived longer than we thought."

Mr Gunn said if the painting was not of a genyornis, a tall, flightless bird which likely resembled a duck or goose, it could be another giant bird as yet unknown to science.

Monash University archaeologist Bruno David said there could be hundreds of thousands of Aboriginal rock art paintings waiting to be discovered around the country, but it was difficult to date them accurately.

But he said the latest find could be the most ancient yet discovered if it is of the genyor-nis.

"We need to excavate the site next year to date the antiquity of the surface. It is a long-term project," Mr David said.

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