Bones found more than a century ago in Queensland once thought to belong to a "giant ancestral pigeon" have been described as the remains of a kangaroo-sized flying turkey that roamed Australia more than two million years ago.

Researchers at Flinders University have carefully re-examined remains of avian megafauna from four states and have concluded that, rather than representing a single ancient bird species, they belong to five different species, one weighing up to eight kilograms and standing taller than a grey kangaroo.

"These discoveries are quite remarkable because they tell us that more than half of Australia's megapodes went extinct during the Pleistocene Epoch, and we didn't realise this until now," said Elen Shute, a Flinders University PhD candidate.

Megapodes are birds that incubate their eggs by burying them in warm compost mounds or underground. Modern Australian megapodes include the malleefowl and brush turkeys.

Scientists say that describing these species is not just a question of taxonomy but can assist in our understanding of how megafauna became extinct.

When the bones were discovered, natural historian Charles Walter de Vis described them as the remains of a "giant ancestral pigeon", Ms Shute said.

"That's not as silly as it sounds because of the shape of the tarsometatarsus, the bottom part of the leg," she said. The genus name Progura means  "early gura", referring to the crowned pigeon still found in Papua New Guinea.

That first description by Mr de Vis at the Queensland Museum in 1888 stood that way for a century before more remains of large extinct birds were found in the Naracoorte Caves in South Australia and a second species was described.

However, in a paper published in 2008, Walter Boles, then at the Australian Museum, claimed they all represented the same species.

This new research by Ms Shute and her colleagues at Flinders University upends that finding.

"With the benefit of new material, we've seen things with new eyes and come to a rather different conclusion," Ms Shute said.

Her work describes birds – the largest of which was more than a metre tall – that lived during the Pleistocene Epoch alongside diprotodons and marsupial lions.

While these birds were chunky, their long wing bones showed they could fly, and probably roosted in trees, according to the researchers.

Ms Shute's study describes those finds from 1888 and the 1970s as two distinct genuses. She also describes two new species of megapode from the Thylacoleo Caves on the Nullarbor Plain in Western Australia.

She also claims discovery of a new genus from the Curramulka Quarry in South Australia.

"The first four are closely related," Ms Shute said. "But the other is a bit like the fifth Beatle; its remains are fragmentary."

But does it all matter?

Liz Reed from the University of Adelaide, who was not connected with the study, said: "It is important to iron out taxonomic issues in order to understand patterns of extinction."

While Dr Reed had not read this recent paper, published on Wednesday in the Royal Society's Open Science journal, she said the group did careful work.

"I'd be surprised if they made unsure claims. With the number of specimens they have looked at, they'd be pretty sure of what they're doing."

Ms Shute said that one of the species described might have lived as recently as 40,000 years ago, overlapping with the arrival of humans in Australia.

Her co-author, Professor Gavin Prideaux at Flinders University, said there was an ongoing debate about what caused Australian megafauna to become extinct: climate or humans.

He said working out what species existed with accuracy was important when trying to answer this question.

"If you don't know what was there, it's hard to speculate on when and why species become extinct," he said.

He said we still didn't have a good understanding of what Australian megafauna species were around and what lived where.

"You can tell all sorts of stories about what causes extinctions but, if your underlying data set has major deficiencies, then you're just telling stories."