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Eagle Raptors were the alpha hunters of Australia 25-million-years-ago. 	Source: © Jacob Blokland / Flinders University

25-Million-Year-Old Raptor Dominated Land and Sky At Australian Lake

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Dating to 25 million years ago, the ‘oldest and most-complete’ raptor skeleton ever found has been unearthed in Australia. The eagle-like remains are distinctive and indicate a hunter that was top of the food chain in the region.

With long-legs and a 15 cm (6-inch) foot-span, the apex sky-predator ambushed koala bears and flamingos. The almost complete fossil of the “Archaehierax sylvestris” was discovered on a remote cattle station near Lake Pinpa in South Australia, near to Coombalarnie Dam, Cooraninnie Dam and Lake Namba.

Palaeontologist Ellen Mather of Flinders University is the author of a new paper about the find that was recently published in the journal  Historical Biology . The researcher explains that during the Oligocene, about 33.9 million to 23 million years before the present, what is now the dry Lake Pinpa was a vast body of water surrounded by lush forests.

The Archaehierax fossil comprised “63-bones” fossil and it has been titled “one of the oldest-known and best preserved” of any fossilized eagle-like raptors every discovered.

Palaeontologists from Flinders University excavating fossils near Lake Pinpa, South Australia. L to R: Aaron Camens, Amy Tschirn, Jacob Blokland and Kailah Thorn. (Image: Trevor Worthy, Flinders University)

Palaeontologists from Flinders University excavating fossils near Lake Pinpa, South Australia. L to R: Aaron Camens, Amy Tschirn, Jacob Blokland and Kailah Thorn. (Image: Trevor Worthy, Flinders University)

A Predecessor, But No Ancestor, Of Today’s Eagles

Professor Mather wrote that the species was slightly smaller and leaner than the modern wedge-tailed eagle, which represents the largest of Australia's surviving eagle species. Ms Mather added that Archaehierax didn’t belong to any of the living genera or families and that it represents its own unique branch of the eagle family, unrelated any of the species that exist today.

The paper explains that the long-legged creature shows many unique features unlike those observed in modern hawks and eagles. Around 25 million years ago, the raptor is thought to have swooped down on: “koalas, possums, waterfowl, cormorants, flamingos and koalas.” The team believe that an aerial assault from Archaehierax resulted in the creature grabbing its prey with its long legs. With a foot span of nearly 15 cm [6 inches] long, large prey measuring the size of “a small dog or large cat” was also on the primitive eagle’s menu, according to the paper.

 

A comparison of the prepared fossil tarsometatarsus (foot bone) and a hypothesized silhouette of Archaehierax sylvestris (left) compared to the wedge-tailed eagle Aquila audax (right). The scale bar is 10 mm long. (Image: Jacob Blokland / Flinders University)

A comparison of the prepared fossil tarsometatarsus (foot bone) and a hypothesized silhouette of Archaehierax sylvestris (left) compared to the wedge-tailed eagle Aquila audax (right). The scale bar is 10 mm long. (Image: Jacob Blokland / Flinders University)

Fairly Slow, But Deadly Niffy

The new research determined Archaehierax wings were short for its length, but making up for this its legs were relatively long. Therefore, with a considerable reach, Archaehierax wasn’t a very fast flier, but it had “agility” meaning it was an effective ambush predator. It is for this very reason the discovery is so rare. Any apex-predator species, at the top of an environmental food chain, are always much fewer in number than the populations of their prey. Why is this the case?

According to a 2010 paper published on Nature titled The Dynamics of Preditation , in any food chain, organisms pass on only part of the energy they receive from food. Thus, with less energy, each higher level in a food chain supports fewer individuals than the one below it, resulting in fewer in number. For this reason, co-author and fellow Flinders University paleontologist Trevor Worthy wrote that the discovery of 25-million-year-old raptors is “exceptionally rare.”

All It Takes Is One Big Discovery

Worthy said finding even a single bone from a Oligocene fossil eagle “is exceptionally rare,” but having found, recovered and studied an almost whole skeleton “is pretty exciting, especially considering how old it is.” According to a report in Daily Mail , Worthy said he has studied the Lake Pinpa site for several years and this “is the most exquisite fossil we have found to date.”

Australia has a broken fossil record of whales, dolphins, and porpoises (Cetacea) from the Early Oligocene, that Museums Victoria say “have been derived from only a few locations.” The reason given for the record of cetaceans being so poor is “because little systematic prospecting has been carried out and all significant fossil cetaceans have been discovered by accident.” The discovery of this rare sky-borne marsupial ambushing raptor is among only a few examples of the species that have ever been discovered, and it is hoped this discovery will help secure more funding for future research in Australian landscapes that are potentially loaded with rare Oligocene fossils.

Top image: Eagle Raptors were the alpha hunters of Australia 25-million-years-ago.       Source: © Jacob Blokland / Flinders University

By Ashley Cowie

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