What ancient eggshells can tell us about extinction

Rachel Sauer — Tue, 21 Jul 2026 19:55:38 +0000

What ancient eggshells can tell us about extinction Rachel Sauer Tue, 07/21/2026 - 13:55

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91��ý Professor Emeritus Gifford Miller contributed to a new study that delivers a more accurate understanding of the extinction of one of Australia’s oversized flightless birds

Some people collect albums. Or coins. Or stamps. 91��ý Professor Emeritus Gifford Miller collects the eggshells of large extinct flightless birds.

That collection came in handy for recent research that’s helping scientists understand more precisely when Genyornis newtoni went extinct in Australia—and whether humans were responsible for their extinction.

Genyornis is a genus of large flightless birds that roamed the Australian outback alongside modern-day emus; they reached heights of about 7 feet and weights upwards of 500 pounds.

Gifford Miller has spent some 20 seasons in the field in Australia collecting the well-preserved eggshells of flightless birds. The samples were pivotal to recent research determining the extinction date of the continent’s largest flightless bird. (Photo: Gifford Miller)

While emus—which are unrelated to Genyornis—survived, the majority of other megafauna on the continent went extinct around the time humans arrived (or just shortly after).

“There was a really big uncertainty in Australia as to how we get precise, reliable ages on when the actual Genyornis extinction occurred,” says Miller, a professor emeritus of earth science who is also the director for the Center for the Geochronological Analysis of the Global Environment at the Institute of Arctic and Alpine Research (INSTAAR). “Radiocarbon dating wasn’t going to do it, and amino acid racemization wasn't going to do it at the precision we wanted.”

To get closer to the truth, Miller encouraged his colleague, Elizabeth Niespolo, a geologist at Princeton University, to try out a different method called uranium-thorium burial dating. The process relies on the eggshells to uptake uranium—which is plentiful in Australian soils—and then produce thorium as a byproduct of uranium decay.

The results of the research were published this summer in a new article in the journal Quaternary Science Reviews, which Miller co-authored.

The megafauna-human overlap

Previous dating methods posited that genyornis went extinct around 60,000–65,000 years ago. However, Niespolo found much different results.

“She thinks she has very firm extinction dates at about 45,000 years ago, which is quite a bit younger than a lot of other people think,” says Miller.

The date that humans arrived in Australia is also still up for debate, with some studies saying they showed up around 55,000 years ago, and others around 65,000 years ago (still a long time ago when the only way to reach the island at that time was via boat, Miller points out).

Either way, the new results would mean there was a very long period of time between the arrival of human colonizers and the extinction of genyornis.

“We’re basically left with two options: either there is a long overlap, which is unusual relative to almost all other human-faunal extinction overlaps, or the early human colonization dates are too old,” says Miller. “Both are plausible.”

Predation or fire?

Now, scientists are left to continue zeroing on that human arrival date, as well as the method by which humans managed to make so many species go extinct.

Genyornis newtoni was one of many species of megafauna that disappeared from Australia around the time of human colonization. (Illustration: Peter Trusler/Monash University)

“There are two options, and both have some strength behind them,” says Miller. “One of them would be predation, particularly of genyornis eggs.” Many eggshells were found with evidence of contact with fire, he says, meaning they were either cooked directly over a fire or discarded near one. “Clearly people were utilizing these eggs as a food source.”

The birds themselves might also have made their way to the dinner plate. “These are very big birds, much bigger than emu,” says Miller. “So, they would be a meal for a whole family for a week or two.”

For his part, Miller is partial to another theory: that humans impacted the landscape by systematic burning of vegetation that was genyornis’ primary food source.

“We have independent evidence from the emu—including a continuous time series from the present back through the extinction window—that shows the entire ecosystem shifted about 45,000 years ago in the central desert area where these birds are most common,” says Miller.

Leveraging the eggshells for further research

Miller is hoping that he and Niespolo might be able to use her now-proven dating methods on other eggshells in his collection to learn everything they can about the last 100,000 years or so on the continent.

“I have this tremendous geographic spread of samples from all across Australia,” says Miller, who hopes they might use that reservoir of material to determine whether the extinction dates changed based on location. “Did it happen earlier or later on the south coast? Or up in the far north near Darwin where the first people must have arrived?”

Miller also believes they can learn more about the historical temperature gradient of Australia using Niespolo’s dating methods on his collection.

“There are some interesting little tidbits that she and I are kicking around,” Miller says. “We’re looking to put together more projects that might capitalize on this amazing resource of samples I have.”

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91��ý Professor Emeritus Gifford Miller contributed to a new study that delivers a more accurate understanding of the extinction of one of Australia’s oversized flightless birds.

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Top photo: Gifford Miller

Center for the Geochronological Analysis of the Global Environment

What ancient eggshells can tell us about extinction

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