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25 million-year-old eagle fossil discovered in Australia

Researchers in Australia have found a nearly complete fossilized raptor skeleton that points toward a unique ancient eagle species.

(CN) — A recently discovered 25 million-year-old eagle fossil found in South Australia appears to be unique to the continent and adds raptors’ long evolutionary history in Australia.

Paleontologists from Flinders University in Adelaide, Australia, have unearthed Australia’s oldest eagle fossils from a remote outback cattle station and in it have found a new fossil species from the late Oligocene era, which ended 23 million years ago.

Named Archaehierax sylvestris, this species of raptor is among the oldest known eagles in the world.

“‘Raptors’ is a more encompassing word than ‘eagles’ — really a raptor is a bird of prey with a hooked bill and large talons, so the word ‘raptor’ also includes the nocturnal raptors: owls. Put another way, not all raptors are eagles, but all eagles are raptors,” said study co-author Travis Worthy, a Flinders University paleontologist, in an email to Courthouse News.

“Our new Archaehierax (pron. ah-kay-hi-rax) does not group with other eagles in the family tree of eagles and hawks — it has primitive characteristics that set it apart and as one of the first branches on the family tree. This is not unexpected given its age. It however is clearly quite different to all the eagles etc. from the Northern Hemisphere, suggesting it was part of a group evolving along its separate line in Australia. Not unexpected given Australia is nearly the same size as the USA,” Worthy continued.

Flinders University Ph.D. candidate Ellen Mather is the first author of the new report, which was published Monday in the peer-reviewed journal Historical Biology.

“This species was slightly smaller and leaner than the wedge-tailed eagle, but it’s the largest eagle known from this time period in Australia,” Mather said in a press release. “The foot span was nearly 15 cm long, which would have allowed it to grasp large prey. The largest marsupial predators at the time were about the size of a small dog or large cat, so Archaehierax was certainly ruling the roost.”

The Australian environment during the Oligocene was very different than today.

The remains of Archaehierax were discovered during university researchers’ ongoing investigation into a lost ecosystem along the barren shore of a dry lake known as Lake Pinpa in what is today a desolate and sandy desert habitat. Australia’s interior was, then, a rainforest with extensive tree coverage and lush forests.

“Now a very dry desert, it was once rainforest. This fossil site gives us one of the best windows into that lost world. Predators are always very rare so to find much of a skeleton was really most unexpected. As it turns out, it is very significant and reveals that Australia had its own Accipitridae, or eagles and hawks etc., 25 million years ago,” Worthy said.

In a press release, Worthy added that eagles are not often found as fossils because, perched atop the food chain, there are simply not many of them. Few individual eagles means fewer opportunities for remains to be preserved.

“It’s rare to find even one bone from a fossil eagle. To have most of the skeleton is pretty exciting, especially considering how old it is,” Worthy explained.

Archaehierax would have hunted koalas, possums and other animals in trees surrounding the vast, shallow Lake Pinpa that also attracted waterfowl, cormorants and flamingos.

Life in forests poses challenges to flying animals. To avoid collisions with trees and branches while hunting, the Archaehierax adapted to thrive in its terrain.

“The fossil bones reveal that the wings of the Archaehierax were short for its size, much like species of forest-dwelling eagles today. Its legs, in contrast, were relatively long and would have given it considerable reach,” Mather said. “The combination of these traits suggests Archaehierax was an agile but not particularly fast flier and was most likely an ambush hunter. It was one of the top terrestrial predators of the late Oligocene, swooping upon birds and mammals that lived at the time.”

Archaehierax is one of the best-preserved partial skeletons found at the site — 63 of its bones were found.

“I have studied this system for many years now, and this is the most exquisite fossil we have found to date,” Worthy said in the press release.

“The completeness of the Archaehierax skeleton allowed us to determine where it fits on the eagle family tree. It shows a range of features unlike any seen among modern hawks and eagles,” Mather said. “We found that Archaehierax didn’t belong to any of the living genera or families. It seems to have been its own unique branch of the eagle family.”

She continued, “It’s unlikely to be a direct ancestor to any species alive today.”

Without further research and discovery, much remains unknown about Archaehierax’s lifespan and history at this time.  

“We can’t say for certain when Archaehierax sylvestris died out; the fossil tells us the species was alive 25 million years ago, but without more material we can’t really determine whether it also went extinct around this time, or if it survived for a few more million years after this,” Mather added in an email. “We also don’t know if it went extinct in the strictest sense (all individuals died out) or because it gradually evolved into new species. It’s an unfortunate reality of Australia having a sparse fossil record for this time.”

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