Avian megafauna plagued by crippling bone disease

Avian megafauna plagued by crippling bone disease

An exceptionally rare fossil discovery by researchers at Flinders University in South Australia has offered a new perspective on the disappearance of a giant Australian bird, genyornis newtoni – and the picture is not pretty.

posting on Papers in Paleontology, researchers describe occurrences of severe bone infections, known as osteomyelitis, in at least four individuals of this ancient species excavated from the salt lake beds of South Africa’s Lake Callabonna Fossil Reserve, about 600 km northeast of Adelaide. . Weighing approximately 230 kg and standing 2 m tall, the imposing Genyornis was the only surviving lineage of Australia’s dromornithids, nicknamed “Thunder Birds”, and this new discovery documents the role of disease in their extinction.

“It’s a rare thing in the fossil record to find one, let alone several, well-preserved fossils with signs of infection,” says Flinders University researcher and lead author of the paper Phoebe McInerney.

“A lot of infections form in soft tissue, which doesn’t preserve very well, so we rely on things that show up in bone.”

The study of disease and trauma in the fossil record, termed paleopathology, is progressing rapidly as diagnostic techniques such as computed tomography (CT) scan be more available. Because bone abnormalities often arise as a result of specific life events, researchers are increasingly able to reconstruct the behavior, physiology, and life histories of extinct fauna.

In the case of Genyornisthe fossil record tells a story of extreme environmental stress and a population pushed to the limits of their physiological tolerance.

Assembling bone fragments from at least 34 individuals, the researchers estimated that a minimum of 11% of the local population in Lake Callabonna suffered from bone disease.

“In most cases, we probably only see 1% to 2% of a population with osteomyelitis,” says McInerney. “It was unusual that we had so many people showing the same signs of infection, suggesting that something was happening in the environment that was causing this population to be more affected.”

A diagram showing the location of diseased bone fragments in genyornis newtoni, with a 1.8m tall male as a size reference.
Location of the bones affected by the pathologies in genyornis newtoni, shown standing next to a 1.8 m tall man. Credit: Phoebe McInerney.

Co-author Associate Professor Lee Arnold, from the University of Adelaide, dated the lake sediments in which Genyornis It was found. Their results indicate that the species inhabited the Lake Callabonna region during a period of severe drought beginning around 48,000 years ago, a time when central Australia transitioned from a landscape of extensive forests and inland lakes to desert plains and salt bushes we see today.

“As drought conditions worsened, food resources would have been reduced, which would have caused considerable stress on the animals,” says co-author Associate Professor Trevor Worthy of the Flinders University Laboratory of Paleontology.

“From studies on live birds, we know that challenging environmental conditions can have negative physiological effects, so we inferred that the Lake Callabonna population of Genyornis I would have been fighting in such conditions,” he says.

“Birds have a very good stress response,” McInerney says, “but if that stress response goes on for a long period of time, they start to reallocate energy from things like their immune systems to things like breathing and brain functions to keep. live. And that’s where you have this increased susceptibility to infection.”

Those who succumbed to the effects of osteomyelitis would have faced a painful decline, says McInerney.

“We see foamy and interwoven bone, large abnormal growths and cavities in their fossil remains,” he explains.

“They would have been increasingly weakened, in pain, making it difficult to find water and food.”

Photographs comparing healthy and infected bones, as well as their location in the body of Genyornis Newtoni.
The infected tarsometatarsus, one of the leg bones of birds, compared to a healthy bone. Credit: Phoebe McInerney.

With the fossil record indicating that this period was probably the last hurrah for Genyornisit is likely that the high rates of disease observed directly contributed to their extinction.

As well as giving us a window into past extinctions, McInerney points out that there are lessons to be learned about the stress faced by modern bird species as our climate continues to warm and dry.

“We should be able to learn from the fact that these animals are now extinct, possibly due to their suffering with this higher rate of infection. We need to apply that to live birds and make sure they don’t go down the same path.”

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