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25 million years ago, an eagle with half a foot long talons tore ancient koalas from trees in Australia, according to a new study.
Paleontologists have discovered 63 fossilized bones from the ancient koala-hunter in 2016, during an expedition to Lake Pinpa, a salt lake east of the Flinders Ranges in South Australia. After carefully examining the bones, the team recently named the new species of eagle Archaehierax sylvestris. The ancient raptor has no direct descendants living today, they determined.
Since the bones date from the Oligocene era, which lasted from 33.9 million to 23 million years ago, the A. sylvestris specimen represents the oldest eagle fossil ever found in Australia, as well as one of the best preserved, scientists reported on September 27 in the journal Historical biology.
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“As top predators, eagles and hawks are less abundant than the species they feed on,” first author Ellen Mather, a doctoral student at Flinders University Adelaide, Australia, told Live Science in a report. E-mail. “This tends to be perpetuated in the fossil record, as there is less chance of an individual of these species being fossilized.”
And when found, eagle fossils often include very few bones – or sometimes just one – which makes the new fossil, with its 63 bones, an exceptionally rare find, the authors noted in their report.
Today, Lake Pinpa, where the fossil was found, rarely contains water and is set in a sand dune landscape sparsely adorned with grass and trees. But back when A. sylvestris soared into the sky, the lake looked surprisingly different, senior author Trevor Worthy, a vertebrate paleontologist and associate professor at Flinders University, told Live Science.
At that time, the Pinpa Lake excavation site was on the shore of a larger lake, or lake system, which stretched about 100 kilometers through a temperate zone. tropical forest. The fossil record indicates that the fish, crocodile and freshwater dolphins populated the lakes, and an array of shorebirds, opossums, and ancestral koalas roamed the shore.
“Lake Pinpa, as a whole, is the richest fossil site for this period in South Australia,” Worthy said. The earliest known ancestors of modern marsupials, such as bandicoots, possums, kangaroos, and wombats, have all been found at the site, along with many avian herbivores, such as ducks and cormorants. But even in this treasure trove of ancient Australian fossils, specimens of hawks and eagles are rare, he said.
When Worthy’s team first discovered the A. sylvestris fossil in 2016, “we knew instantly we had a large bird, but it was very fragmented and therefore not spectacular,” he said. Among the first bone fragments they excavated, the team found claws and a lower leg bone called the tarso-metatarsus; these bones revealed that the specimen was an eagle, but at that time they did not know what species. So they carefully collected the bones in a large piece of sediment, encased everything in plaster, and returned the specimen to their lab.
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Worthy and the team then carefully freed the bone pieces from their surrounding sediment, one piece at a time, and sawed all of the pieces together into whole bones. Some bones contained as many as 20 tiny fragments, Worthy said. Mather then compared the assembled bones with those of various hawks, ospreys, eagles and hawks. Based on this analysis, she determined that the fossil belonged to a family of raptors called Accipitridae, which includes hawks, eagles, kites, and Old World vultures.
That said, the specific characteristics of the new fossil, such as the spacing of its toes and the insertion points for its leg muscles, set the bird apart from other members of the Accipitridae family, Mather said. Based on these characteristics, along with the age of the Pinpa Lake site, the team concluded that the bird belonged to a previously unknown subfamily and species of eagle.
“We can be sure that the fossil represents a new species as the only other species of eagle of a similar age, Pengana robertbolesi from Riversleigh, Queensland, has a very different morphology from Archaehierax“said Mather.
The unique characteristics of the A. sylvestris the bones also hinted at the ancient bird’s hunting style. The eagle had a 5.9 inch (15 centimeter) foot wingspan and long legs compared to its overall size, meaning the predator was equipped with the perfect tools to reach out and catch large prey at the treetops. And the eagle’s relatively short wings suggest that while it does not fly particularly fast, A. sylvestris probably excelled at dive-bombing unsuspecting koalas from above.
Although eagle fossils are generally difficult to find, at some excavation sites they are relatively common, Mather noted. For example, in the La Brea Tar Pits in Los Angeles, eagles and other predators got trapped in the tar while trying to eat other animals in the pits; this means that today a good number of predator fossils can be found at the site.
“However, this is not the case at Pinpa Lake,” where no specific environmental feature favors preservation from predators, said Mather. “The fossilization of our eagle was a matter of luck.”
Originally posted on Live Science.
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