25-million-year-old eagle fossil adds new branch to family

Palaeontologists have uncovered the fossilised bones of a 25-million-year-old eagle. It’s a previously unknown species – and one of the oldest eagles in the world.

“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,” says Ellen Mather, a PhD candidate at Flinders University and first author on a paper describing the fossil, published in Historical Biology.

“I have studied this system for many years now, and this is the most exquisite fossil we have found to date,” says Trevor Worthy, associate professor of palaeontology at Flinders and co-author on the paper. The partial skeleton has 63 bones.

“With eagles at the top of the food chain, they are always few in number – and so are infrequently preserved as fossils,” adds Worthy.

“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.”

The eagle has been named Archaehierax sylvestris, which translates from ancient Greek as “ancient hawk of the forest”.

“The foot span was nearly 15 cm long, which would have allowed it to grasp large prey,” says Mather.

“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 researchers found the eagle bones on the shores of Lake Pinpa, in northwestern South Australia. Lake Pinpa has previously been the site of other 25-million-year-old fossil discoveries, like giant wombats.

During this time period – the late Ogliocene – the local environment would have been a verdant forest. Mather says that the bones of the eagle reflect this.

“The fossil bones reveal that the wings of 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.”

The shorter wingspan means that the bird was less likely to collide with trees and branches mid-flight.

“The combination of these traits suggest Archaehierax was an agile – but not particularly fast – flier and was most likely an ambush hunter,” says Mather.

While fearsome, the ancient eagle is likely a distant relative of living eagle species.

“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,” says Mather.

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

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