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A 25-million-year-old eagle fossil found at a remote breeding station in the hinterland of South Australia has been identified as one of the oldest species of raptor in the world.
Paleontologists discovered the eagle fossil on the shore of a dry lake known as Lake Pinpa in 2016, and have since identified it as a new species, Archaehierax sylvestris, in a study published in the journal Historical Biology.
Ellen Mather, a PhD candidate at Flinders University and the study’s first author, said the ancient bird was slightly smaller than a wedge-tailed eagle, with a wingspan of six inches.
“It would probably have been one of the bigger eagles of the time, as far as we know,” she said. Although Pinpa Lake is now a sandy desert habitat, 25 million years ago it was likely a temperate rainforest with permanent water bodies.
“We think it probably would have attacked most of the small to medium-sized birds and mammals that were also alive at that time, so things like the ancestors of modern opossums and koalas living in the forest,” in addition to other birds such as ducks and possibly flamingos, Mather said.
The eagle had relatively short wings for its size, but long legs. “It’s pretty common among forest eagles,” Mather said. “It’s an adaptation to essentially have to fly in a more crowded space compared to eagles that live in more open spaces like meadows or woods.”
“We think it would have been an ambush hunter. So even though he’s not very fast, he would have been quite nimble, able to make quick turns and probably would have waited [on] a perch for prey to roam within striking distance.
Mather said the discovery showed Australia had an endemic lineage of eagles early in the history of animal evolution. The ancient bird belonged to a separate branch of eagles and was not the direct ancestor of any living species.
“This shows that there are still 25 million years, this family [the Accipitridae] was widely distributed around the world but also already diversifying, and Australia seems to have been a unique place of diversity even then.
The ancient eagle exhibited a number of different characteristics than modern hawks and eagles, including a wider foot wingspan for capturing prey.
“Some of the muscle insertion points on the leg were quite deep compared to most living accipitridae [the family of birds including hawks and eagles] so that might suggest a pretty strong grip… given its pretty thin build, ”said Mather.
Over 60 ancient eagle bones have been recovered, making it one of the best-preserved fossils found at the Pinpa Lake Breeding Station. Ancestors of many other Australian species, including wombats, platypus and kangaroos, have also been found at the site.
It was likely that the eagle specimen was taken to a lake when it died. “These bones would have been buried in the sediment at the time, which allowed them to be preserved,” Mather said.
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