Unique remains of possibly the world’s largest bird found in Australia

A pair of legs belonging to what may be the largest species of bird to ever roam the planet has been unearthed at an outback fossil site in central Australia. Excitingly, other remains may lie nearby, waiting to be unearthed.

Described by one paleontologist as an “extreme evolutionary experiment,” Stirton’s Thunderbird (Dromornis stirtoni) is a patchwork of odd anatomical features. Its oversized beak protrudes from an undersized skull all perched on a body that towers 3 meters (10 ft) tall and weighs up to half a ton.

Just to make the animal sound even more absurd, these 8 million year old lumbering giants actually are related to modern poultrylike chickens and ducks.

While the oversized “Demon Ducks” are undoubtedly heavyweights, getting an accurate measure of their size from a jumble of bones is easier said than done. This latest finding could take the guesswork out of models trying to describe the true size ranges of dromornis Species.

For the first time, remains of these massive flightless birds have been found articulated, arranged more or less as they existed inside the once-living animal.

A great moment at #alcoota2022 with the very first articulated -Dromornis stirtoni- leg unearthed at Classy Corner. Many Thanks @phoebyornis for scale! #fossilfriday @fupalaeosoc @FlindersPalaeo pic.twitter.com/mJaKvacOtg

— Museum and Art Gallery of the Northern Territory (@MAG_NT) July 22, 2022

“This means the carcass was complete when buried,” Adam Yates, paleontologist and curator of earth sciences at the Museum and Art Gallery of the Northern Territory, told ScienceAlert.

“We only have the lower legs because we dug so far. There is an expectation that much of the remaining skeleton – if not all of the skeleton – could lie in the next dig if we dig further into the embankment the legs are coming from.”

The fossilized bones were discovered in the Alcoota Reserve, a dense fossil deposit 190 km northeast of Alice Springs that contains one of the largest concentrations of terrestrial vertebrates in Australia. While this site has yielded thousands of fossilized specimens since excavations began in 1986, most of them are jumbled fragments of different species, as historic floods have muddled the remains.

Therefore, most Alcoota fossils had to be carefully sorted by species and reconstructed using parts from several individual animals. Such composite reconstructions necessarily involve some degree of creative thinking that introduces occasional errors.

“Even if you put all the species together correctly — you put the right bones together with the right species — you’re still going to have proportional errors, because of course there are natural differences between individuals,” Yates explains.

The new legs are an exciting find because they can give researchers a much more accurate idea of ​​the true proportions of these animals. It will also help paleontologists identify more D. stirtoni Bones from the other jumbled fossils in Alcoota.

Deb’s drumstick now in one piece. #FossilFriday pic.twitter.com/lrtzobn0oP

— Sam Arman (@Samosthenurus) September 2, 2022

Flinders University paleontologist Warren Handley, Yates and colleagues had previously compared a mess D. stirtoni Bones discovered in the region and were able to identify a size difference between males and females.

They took bone samples and identified a type of tissue called marrow bone in the smaller specimens. This is a temporary storehouse of calcium that females shell their eggs from, a trait males lack, explains Yates.

Judging by the size of the newly discovered leg bones, researchers suspect the remains belong to a woman D. stirtoni, which the team dubbed Deb. They intend to do a histological test to confirm their suspicions.

Meanwhile, Deb’s fossils are being prepared for a temporary display at the museum later this year. Carefully cleaned and hardened with a plastic acetate fill any gaps The bones are saved for future studies.

Traces of thunderbirds have so far only been found in Australia and date to the late Miocene. These absurdly bloated chickens with small stub wings lacked the specialized keeled breastbone that other birds rely on for their large flight muscle attachments. They roamed dry forests and probably used their huge beaks to devour fruit and other plants.

Other herbivores found in Alcoota from the same period include marsupials such as wallabies and ancient cow-sized wombat relatives.

These finds suggest so D. stirtoni was the great browser of this arid ecosystem, similar to today’s camels — it used its height to reach vegetation out of reach of its smaller herbivores, Yates explains.

Back then, “it wasn’t a mammal that took on that role, it was a bird,” says Yates.

Fossil finds suggest these epic birds and their relatives existed for a staggering 25 million years. But at the end of the Miocene, Australia dried up, perhaps too quickly for that D. stirtoni to adjust.

Yates notes that juvenile thunderbird fossils are extremely rare to find, suggesting these animals did not have a rapid reproductive rate and may only have produced one or two chicks per year. In addition, “it has taken an extraordinarily long time for a bird to reach maturity. dromornis took 15 years to reach adult size and sexual maturity.”

These traits are known to make animals vulnerable to changing environmental conditions.

In the corner of the fossil site where the paleontologist found Deb was also an articulated wallaby, so Yates is keen to get back in the field next year. He’s confident there’s more of Deb in the earth bank to be discovered, and there’s the tantalizing possibility that this site also contains articulated fossils of unknown species.