A reconstruction of Progura, right, alongside a kangaroo and modern bush turkey. By Elen Shute, from photos by Kim Benson, Tony Rodd and Aaron Camens.

A giant, flying turkey as tall as a kangaroo is among five extinct large megapode birds discovered by palaentologists at Flinders University.

All five birds were chunky relatives of today’s Malleefowl and Brush-turkeys, but the giant brush-turkey Progura gallinacea, which was as tall as a grey kangaroo, soars above the others.

After carefully comparing megapode fossils from Queensland, New South Wales, South Australia and Western Australia, the researchers have concluded that the remains belong to five different extinct species ranging from 3 to 8kg in weight. That’s up to four times the size of a modern Malleefowl, which weighs in at around 2kg.

The big birds lived during the Pleistocene, alongside Australia’s giant extinct marsupials such as diprotodons, marsupial lions and short-faced kangaroos.

“These discoveries are quite remarkable because they tell us that more than half of Australia’s megapodes went extinct during the Pleistocene, and we didn’t even realise it until now,” said Flinders PhD candidate and researcher Elen Shute.

“Given several of the largest birds to have lived in Australia in recent times have escaped detection in the fossil record until now, our research shows how little we know of Australia’s immediate pre-human avifauna. Probably many smaller extinct species also await discovery by palaeontologists,” said Trevor Worthy.

The extinct megapodes include the ‘tall turkeys’ in the genus Progura, which had long, slender legs, and the “nuggetty chickens” – species with short legs and broad bodies – for which a new genus Latagallina has been made.

It seems that none of these giant megapodes built mounds like their living Australian cousins because they lacked the large feet and specialised claws seen in mound-builders.

It’s more likely that they buried their eggs in warm sand or soil, like some living megapodes in Indonesia and the Pacific.

Unlike many large extinct birds, such as dodos, these megapodes were not flightless. While big and bulky, their long, strong wing bones show they could all fly, and probably roosted in trees.

The latest findings have been more than a century in the making. The first giant megapode species was described from Queensland in the 1880s, and another slightly smaller species was described from South Australia’s Naracoorte Caves in the 1970s.

Since then, the status of the two species has been questioned, and it had been suggested that they were only one species that later dwarfed to become the modern Malleefowl.

The new evidence shows that this no longer stacks up.

“We compared the fossils described in the 1880s and the 1970s with specimens discovered more recently, and with the benefit of new fossils, differences between species became really clear,” said Ms Shute.

“The two species that were originally described are so different that they belong in separate genera. These and three more new species were all more closely related to each other than they are to the living Malleefowl.

“What’s more, we have found bones of Malleefowl in fossil deposits up to a million years old, alongside bones of three extinct species of various sizes, so there’s really no evidence that dwarfing took place.”

Two of the new species come from the Thylacoleo Caves beneath the Nullarbor Plain. These caves, discovered 15 years ago, have proved to be a treasure trove of new species.

“So far the Thylacoleo Caves have yielded seven new species of kangaroo, a frog, two giant ground-cuckoos, and now two new megapodes,” said Gavin Prideaux.

“The closer we look, the more we keep finding.”