Set of articulated legs belonging to prehistoric flightless bird uncovered at Alcoota fossil site - petsitterbank

Set of articulated legs belonging to prehistoric flightless bird uncovered at Alcoota fossil site

A set of female articulated legs belonging to the prehistoric Dromornis stirtoni discovered in Central Australia is expected to give researchers more accurate information about the size of the largest bird known on Earth.

Dromornis stirtoni, also known at Stirton’s thunderbird, was a large flightless bird thought to have stood about 3 meters high and weighing up to 650 kilograms, which once roamed a site in Central Australia 8 million years ago.

It is at this site, Alcoota, 250 kilometers north-east of Alice Springs, where the first-ever set of female articulated legs were uncovered by Museum and Art Gallery of the Northern Territory senior curator of earth sciences, Adam Yates, and his team of scientists.

“That is, the bones from a single individual were buried in the ground in their anatomical position,” Dr Yates said.

He said uncovering the legs had given them vital information about the size of an individual Dromornis.

Toe bones from a female Dromornis stirtoni.(ABC Alice Springs: Emma Haskin)
A sketch of a large bird with a brown body, black neck and an orange beak.
A recent sketch of what Dromornis stirtoni may have looked like, by Dr Yates.(Supplied: Adam Yates)

“It enables us to, for the first time, accurately see the proportions of a single individual,” Dr Yates said.

“We know this is one individual. It had a drumstick of a certain length and had a foot of a certain length.”

Dr Yates said the team would be able to reconstruct a more accurate skeleton based on the find, rather than “piecing skeletons together from a jumble of bones and making what we would call a composite, which is going to, by necessity, include some proportional errors”.

He knows that the bird’s legs are an adult female thanks to a size differential, and by looking at the cross section of the bone tissue.

“We know that the little ones were the females because they have a peculiar type of tissue that you find inside the inner cavities of bones that is called medullary bone,” he said.

Bones lying in dirt, with brushes on the ground nearby.
This is how the articulated legs looked when they were found at the Alcoota fossil site.(Supported by Trevor Worthy)

Exciting find

Dr Yates said the discovery was exciting and he hoped there would be more of this individual female found.

“There’s probably the rest of this Dromornis. You’re not going to have two legs side by side and not the rest of the skeleton,” he said.

Dr Yates suspects the rest of the skeleton is buried in a bank because parts of the Dromornis’s pelvis were also found in the bank.

The back view of two people working at the dig site.
Tim Niederer and Fraser Brown, PhD students at Flinders University, were part of the volunteer crew working at the site.(Supported by Trevor Worthy)

“I’m confident that we’ll have at least a large part of the body,” he said.

“Hopefully, if we’re really lucky, the entire neck and at the end of the neck, the head, then that would be super fantastic.”

There is still much that Dr Yates and his team do not know about the bird that has been studied for several decades.

“We don’t know basic things like how many bones were in the neck of a Dromornis or how long its neck was,” he said.

“We have an estimate based on the number of neck bones that we found … so we can sort of roughly guess that there’s probably more than 10 and less than 20 bones in its neck, but we don’t know the precise number.”

new chapter

Dr Yates is excited about what other secrets might be unearthed at Alcoota.

A skeleton of a large, flightless bird, against a black background.
A full skeleton of the Dromornis stirtoni.(Supplied: Museum of Central Australia)

“It would also be great to see a complete skull … the skulls that we found to date have all fallen apart and they’ve been assembled from loose bits.

“I’m very excited about the possibility of other skeletons of other creatures, things that we really don’t know what they look like,” he said.

Dr Yates said the find could be a new phase and chapter in excavations at the site.

“We’re actually getting skeletons instead of just loose bones,” he said.

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