Piecing together the prehistory of Australia’s birdlife reveals stunning insights.
As far back as I can remember I’ve been fascinated with dinosaurs and megafauna, and I’ve wanted to know more about them. From at least the age of five, I knew I wanted to be a palaeontologist.
That interest has stayed with me over the years. After graduating from Adelaide University with a Bachelor of Science in evolutionary biology, I came to Flinders University in 2016 and took on a project with Professor Trevor Worthy looking at 20 million-year-old fossils of rails, a type of waterbird, from New Zealand. That was my introduction to bird fossils. I then went on to do a PhD project from 2017 to 2021 on Australian eagle fossils from across different time periods, and I’ve been working on them ever since.
Most of our fossils come from caves. When animals die, bones left on the surface quickly erode away. But caves protect bones from the elements and provide an environment that allows them to be more easily preserved. Some caves are fairly easy to access, but sometimes you have to put on all the caving gear, take lighting with you, and go down these very steep, deep holes to get down to the bottom.
We found some stunning fossils at the end of last year, which are part of an upcoming publication. We went into a cave in the Flinders Rangers of South Australia, hoping to find more fossil material of an eagle specimen that we knew had been found there previously, back in the 1950s and ’60s. We thought there might still be some fossil bones that were overlooked.
We ended up finding quite a lot more than we expected, which was a thrill. We found just over two dozen more bones of the eagle, as well as lots of isolated fossils of small birds and mammals that probably ended up there by accident or were brought in by predators like owls.
Our next publication describes the eagle fossils as a new species from the Pleistocene (2.5 million to 11,000 years ago), which is quite a recent extinction, relatively speaking. It would have been very impressive to see in flight – based on the bones we have, we estimate it to be around twice the size of a wedge-tailed eagle.
We also recently undertook a review of fossil eagle bones collected from the Wellington Caves in NSW to identify more material from a species found by the Warburton River in SA over 100 years ago. Back when this fossil was discovered it was thought to be an eagle. But we looked at the tarsometatarsus, which is the lower leg bone where the foot connects to the leg in birds. This bone is very different in vultures and eagles. In eagles, you can see a lot of scarring from its musculature, and it’s quite robust and powerful because it needs to sink its claws into prey and hold on. But because vultures don’t actively kill their own prey, they have much shallower, more reduced muscle attachments comparatively.
It became quite obvious to us that this fossil bone had to come from a vulture rather than an eagle. This was a stunning discovery – vultures obviously don’t exist here anymore. This was a unique Australian bird that belongs to a group known as the Old World vultures, found throughout Asia, Europe and Africa.
We think their extinction is most likely connected to the extinction of Australia’s megafauna, which occurred at the end of the Pleistocene, about 40,000 years ago. Animals like Diprotodon and the giant kangaroos and wombats would have been providing a lot of the carcasses necessary for vultures to survive on. But when they died out, the vultures’ main food supply would have dried up.
I have also published a paper on Australia’s oldest known eagle, from a 25 million-year-old species found in South Australia. This one was found out in the desert, in a very arid zone near Lake Frome. That is different to cave work! You’re sweating all the time, you have to watch out for the flies, wear sunscreen and sunglasses – it’s quite a challenging experience.
All these discoveries are very exciting, because we don’t have an extensive fossil record of eagles in Australia. They’re not very abundant in most depositional environments, which are typically formed in aquatic or semi-aquatic regions. Finding even a few eagle bones can tell us so much.
The next big thing? I now really want to know what was going on with our eagles between the period 25 million years ago and the Pleistocene, because there’s a big gap there. We don’t know of many species at all from that time period.
This could tell us a lot about the diversity of these species of eagles and the Australian vultures before they died out in the late Pleistocene. Fossil species from that time period could indicate whether our eagles have been long-term inhabitants evolving over time, or if we’re getting sequential extinctions, with new species arriving from elsewhere to take their place. We would discover whether the driver for diversity is endemic evolution or continual migration from overseas.
Our magnificent wedge-tailed eagle is part of the same genus as 10 other species from around the world. It’s closely related to species like the golden eagle from across the northern hemisphere, Bonelli’s eagle from northern Africa, southern Europe and parts of Asia, and Verreaux’s eagle from southern Africa. It’s a very close relative to Gurney’s eagle in the Indonesia-Papua New Guinea region, which is not unexpected given their geographic closeness.
That might suggest it’s a much more recent arrival than you’d think – which is a pretty similar story for most of Australia’s other eagles and hawks. Only the black-breasted buzzard and the square-tailed kite are completely unique to Australia. There’s so much more we need to understand.
Dr Ellen Mather is a palaeontologist specialising in the identification of previously undescribed fossil eagles and their relatives in Australia.