The central Australian outback was once home to a large flightless bird thought to be the largest bird ever to walk the planet.

The goose-like Dromornis stirtoni is thought to have stood about three metres tall and weighed up to 650 kilograms, making it heavier than the Giant Moa of New Zealand and taller than the Elephant Bird of Madagascar.

More is being discovered about this giant, flightless creature from extensive digs at a the fossil-rich Alcoota site, 200 kilometres north-east of Alice Springs.

Dr Adam Yates, the senior curator of Earth Sciences at the Museum and Art Gallery of the Northern Territory in Alice Springs, said the site was about 8 million years old.

But Dr Yates said, relatively speaking, that was not considered that old.

He said it was often difficult for people to conceptualise how long ago creatures like Dromornis stirtoni walked the earth.

"One of the tricks we can use is to talk about analogies," Dr Yates said.

"One analogy I like to use is talk about a piece of paper representing a single year.

A full skeleton of the large, prehistoric bird found at the Alcoota fossil beds. ( Supplied: Museum and Art Gallery of the Northern Territory )

"So if you just lay down one piece of typing paper that's one year and then you build up a stack of 300 pieces of paper, which is less than an inch thick. Then you've covered all of European history in Australia.

Previous work undertaken by Americans

"You'd need a stack that was close to head height to cover all of Aboriginal history in Australia but to get the mere eight million years ago you'd need a stack of paper that was at ground level in Alice Springs and stacked up above Mount Gillen [914 metres].

"To get back to the dinosaurs you'd have to be up where the commercial aeroplanes are flying."

The history of the Alcoota fossil site as scientific research area started back in the early 1960s.

Dr Yates said back then that most of Australia's palaeontology work in the field was undertaken by Americans.

He said as a result, much of what was discovered there at that time went back to the US where it still is, at the Museum of Palaeontology in Berkeley in California.

Fast forward 20 years to the 1980s the Museum and Art Gallery of the Northern Territory had developed its own program.

Working in main pit at the Alcoota dig site in Central Australia. ( Supplied: Museum and Art Gallery of the Northern Territory. )

According to Dr Yates, today's museum holds the largest collection of Dromornis stirtoni fossils in Australia.

It is also in the process of making the collection more accessible to tourists and residents at a central location in Alice Springs.

Uniquely flightless family

He said the story of Dromornis stirtoni was interesting in that for decades scientists mistakenly believed it was distant relative of the emu because the leg bones were similar to those of emus.

A Dromornis stirtoni breast bone found at the Alcoota fossil site, north-east of Alice Springs. ( Supplied: Museum and Art Gallery of the Northern Territory Gallery )

But Dr Yates said thanks to the later discovery of Dromornis skulls at the site, it was revealed that they were actually a flightless family of dromornithids unique to Australia but completely unrelated to emus.

"That discovery is largely down to my predecessor here at the Museum and Art Gallery of Northern Territory, Peter Murray, who started the Northern Territory excavations at Alcoota," Dr Yates said.

Dr Yates said the research took a while, but through a combination of the fossil skulls found at Alcoota and at Bullock Creek — another fossil site 700 kilometres south of Darwin — it was found that Dromornis stirtoni was related to ducks and geese.

He said scientists now believed Dromornis stirtoni was the largest bird that ever lived on the planet.

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