Fossil Of Eagle From 25 Million Years Ago Discovered In Australian Outback

Archaehierax sylvestris was a tropical eagle that lived 25 million years ago in what is now a barren desert. Image Credit: Jacob Blokland/Flinders University

Australia is a weird place, biologically speaking. Most of the mammals that live there – and practically all of the reptiles and amphibians – can’t be found anywhere else on Earth. Species that look practically identical to animals from elsewhere in the world often turn out to be miles apart from them, evolutionarily speaking. It’s a land where toads get horny with gigantic pythons, birds steal your trash, and everything is trying to kill you. Like we said: weird.

What’s more, it’s always been like that – as a new discovery, detailed in a paper published today in the journal Historical Biology, has shown. Found in a remote cattle station in the outback of South Australia, Archaehierax sylvestris is an astonishingly well-preserved eagle fossil from 25 million years ago that is set to change the way we think of ancient Australia.

“With all those little mammals sitting about in trees and nice ducks and flamingos in the lake, some kind of predator would be expected,” study co-author Trevor Worthy told IFLScience. “Now we have one and can see that it is quite different to any from the Northern Hemisphere – so Australia was already going its separate ways, biota-wise.”

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A closeup of the Archaehierax sylvestris fossil as it appeared in the field. Image Credit: Flinders University

The Australia of 25 million years ago – the late Oligocene period of ancient history – was very different from the land we know and fear today. A. sylvestris may have been discovered “in arid desert, with 40+ degrees Celsius and millions of flies,” Worthy explained, but it lived in verdant forest, swooping down on any koalas or ducks that happened to wander too close.

“We know from the fossil bones that Archaehierax sylvestris had short wings, long legs, and had a slender build,” PhD student and study first author Ellen Mather told IFLScience. “We know from the fossil bones that Archaehierax sylvestris had short wings, long legs, and had a slender build. Its beak was not as large or sharply hooked as some of our modern eagles like the wedge-tail. Interestingly, the toes seem to have been more widely set apart on its foot than in any other known living or fossil species. This might have been related to prey capture, giving the foot a wider span when the toes were fully extended.”

It was “absolutely within the family Accipitridae … the hawks, eagles and old world vulture family,” agreed Worthy, and it shared many physiological features of that group. But evolving in the isolation of Australia – which back then was even further south than today – meant that it would have had some noticeable differences too. The bird “didn’t belong to any of the living genera or families,” Mather explained in a statement, and it’s unlikely the new species is a direct ancestor of any modern species.

“What this find has demonstrated is that Australia was playing a major role in the evolution of the Accipitridae […] during this time period,” Mather told IFLScience. “Most fossil eagles/hawks of this time are known from the northern hemisphere, which is where the family is thought to have originated; the existence of a unique Australian lineage demonstrates that not only was this family widespread across the globe by this time, it was already diversifying.”

A comparison of the prepared fossil tarsometatarsus (foot bone) and a hypothesized silhouette of Archaehierax sylvestris (left) compared to the wedge-tailed eagle Aquila audax (right). The scale bar is 10 mm long. Image: Flinders University

The discovery of A. sylvestris is remarkable for quite a few reasons. It’s one of the oldest eagle-like raptors in the world, the team explained, and astonishingly complete – “all the information I gave you above was only possible because so much of the skeleton was preserved, which allowed us to compare it to living eagles,” Mather told IFLScience. By the time the team had finished the arduous process of excavating and cleaning the fossil, Worthy explained, they had 63 bones, with only its femur and humerus as missing key pieces.

“It’s a fantastic find that comes along very rarely,” Mather said.

The excavated block containing Archaehierax sylvestris ready to be plaster jacketed for transport back to Flinders University Palaeontology Lab. Image: Flinders University

More than that, it may the first piece of a puzzle that has global significance, the authors explained. More than half of all birds alive today belong to the order Passerine, also known as songbirds. The ancestors of these species are still a mystery, though – all we know is that they came from Australia.

“We have yet to find the origins of Australian parrots, and pigeons, what were those flamingos that seemed so common – but the biggest question concerns the songbirds,” Worthy told IFLScience. “We know Australia was the origin of songbirds […] sometime in the Oligocene. This fauna is from the end of the Oligocene 25 million years ago – there are songbirds in it and they are so far undescribed.”

“Knowing what these earliest songbirds are is a key question of global importance,” he concluded.

 
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