Ancient eagle fossil discovered in South Australian outback among oldest in the world

By Angela Heathcote September 28, 2021
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The eagle was similar in size to the wedge-tailed eagle and preyed upon koalas.

A 25-million-year-old eagle fossil has been discovered in outback South Australia.

The remains were first found in 2016 and have been described as an entirely new species in the journal Historical Biology today.

Before this discovery, the oldest-known eagle in Australia was Pengana robertbolesi from Riversleigh, Queensland. This new species, dubbed Archaehierax sylvestris, could be older than Pengana by up to a few million years, making it one of the oldest eagle fossils in the world.

Archaehierax sylvestris was similar in size to Australia’s largest living raptor, the wedge-tailed eagle, however it belongs to an ancient lineage of eagles with no direct descendants among modern species.

According to Flinders University PhD student and lead author of the paper Ellen Mather, Archaehierax sylvestris was perfectly attuned to living in a forest environment. 

“The bones reveal that this species had short wings and long legs for its size – something we also see in modern eagles and hawks that inhabit enclosed forests, and which also tend to be ambush predators,” Ellen says. 

“The toes on its foot seem to have been more widely set apart than in any other known species, which might have been to increase foot width for prey capture.” 

The eagle’s diet is said to be made up of everything from koalas to flamingoes, which existed in Australia before the inland lakes dried up.

This particular fossil was discovered at Lake Pinpa, a rich fossil site a seven hour drive north of Adelaide. Just last year, a new species of skink closely related to the blue-tongue lizard was discovered at the same site. 

Ellen says finding a complete eagle fossil is very rare. “The reason for this is largely due to their role as apex predators in their environments, which to function require that there be far fewer predators than prey. With fewer individuals, there are fewer chances an eagle will be fossilised when it dies.  

“Bird bones are also very fragile, which makes them more prone to breaking before they can be fossilised. In our case, this individual of Archaehierax sylvestris probably had its remains end up in the lake soon after it died, which resulted in the remaining bones being buried and preserved.”

In the future, Ellen would like to digitally reconstruct the skeleton of Archaehierax sylvestris to gain more insights into the bird’s ecology. 

“I’d also hope that we might find more fossil material of Archaehierax in future from Lake Pinpa – but of course, that is largely up to luck.”