Using a new technique called paleoproteomics, an international team of researchers studied proteins extracted from fossilized eggshell shards. They compared them to proteins encoded in the DNA of living birds and found that they did not resemble any of the genomes of modern species closely related to extinct small fowl.
The shells, they decided, most likely came from the 500-pounder Genyornis. Their finding is “essential to understanding how the early peoples of Australia interacted with their new environment,” the paper notes. Yet it could also shed light on an even bigger scientific mystery about the disappearance of the planet’s megafauna – the gigantic animals that once roamed the continents.
“This is one of the few scientific questions that almost everyone knows something about,” said Gifford Miller, a professor of geological sciences at the University of Colorado and a lead member of the research team.
Earth was once traversed by dozens of megafauna, including mastodons in North America and armadillo-like glyptodonts in South America. Then they disappeared. Some scientists say climatic events wiped them out. Others blame early humans and the hunt that sustained their growing numbers.
Miller is in the second camp, and the ancient cream-colored eggshell fragments he began collecting in 1992 are the key to his conviction. An Australian paleontologist had previously deemed this shell remarkable for the huge eggs that were its source and speculated that a single bird, known from its fossilized bones, was large enough to have laid them.
Miller wanted to determine when the continent’s megafauna menagerie — the flightless Genyornis as well as a 7-foot-tall kangaroo, a 23-foot-long reptile, and a van-sized marsupial — went extinct. He hoped to answer if humans had ridden them and possibly caused their demise.
But dating the death of these and other alien species had been impossible. Not only are megafauna bones relatively rare there, but carbon-14 dating could only show that the animals had been gone for at least 40,000 years.
However, eggshells of the type identified as Genyornis eggs are common, and Miller, a specialist in geological dating, realized that the durable proteins in the shell could serve as clocks. Amino acids, the building blocks of proteins, have structures that can be configured with a left or right twist. After living things die, the ratio between the two configurations changes at a predictable rate in a process called racemization. Measuring this ratio can reveal how much time has passed since death.
To date, Miller has collected around 150,000 shell pieces presumed to be from Genyornis birds and showed that no eggs were laid more than 45,000 years ago. Using different methods, other researchers have dated the arrival of people to Australia to at most around 60,000 years ago. Both timeframes signal an overlap of thousands of years between humans and the megafauna below.
In 2016, however, a study directly challenged Miller’s work. A team led by paleontologist Trevor Worthy from Australia’s Flinders University said the shells did not come from a Genyornis but from a megapode, a family of hardy birds whose descendants are still found on the continent and on the islands of the Western Pacific. Worthy’s main argument was that the eggs in question would have been too small for a massive bird like Genyornis. He and two co-authors also claimed Genyornis eggs would have a thicker shell with more surface texture.
If true, that meant Miller had spent three decades focusing not on one of history’s greatest birds – in a futile effort to help investigate an extinction theory – but on one that would barely fill a family bucket of KFC chicken. It was a real scientific debate, but it was also a matter of pride for the American: “I took it as a personal affront if my story suddenly wasn’t about megafauna anymore. [but] a stupid little megapode bird.
Once again, he turned to molecular techniques to determine where the egg-laying bird would be on the tree of life. Establishing this by DNA was not possible; the DNA of the eggshell pieces had degraded too much due to their age. Proteins are more durable, and Miller, an Australian molecular biologist and British biochemist, realized they could use them to identify Genyornis.
The trio brought in Beatrice Demarchi, a biomolecular archaeologist from the University of Turin. She pulverized pieces of shell and analyzed the proteins she extracted in a mass spectrometer, an instrument that sorts molecules by passing them past a powerful magnet. With the output of the machine, she could identify the order in which the amino acids had been linked together.
Although no DNA from the descendants of Genyornis exists – its entire line is extinct – the genomes of more than 350 modern birds, including a megapode, have recently been cataloged thanks to a collaboration involving the University of Copenhagen, the Smithsonian National Museum of Natural History, Rockefeller University and other leading research institutes.
Demarchi and several colleagues compared the amino acid sequence of eggshells with sequences inferred from database genomes. At that time, the team had 14 members from Australia, the United States, several European countries and China. The results, according to their new paper, rule out a megapode as the source.
The protein sequence “is very different from a megapode,” Demarchi said in an interview. “It’s more consistent with Genyornis.”
Worthy is not convinced. He says researchers cannot reliably predict the molecular fingerprints of extinct megapodes based on those alive today, as Miller’s team did. “So I don’t think they’ve closed the case,” he noted in an email.
Chris Johnson, an ecologist at the University of Tasmania who has written a book on Australia’s megafauna, has a different view. The protein analysis was impressive, he said via email, and such studies “could really change the science of paleontology.”
Still, Johnson isn’t sure if determining whether a larger or smaller bird laid the eggs is so important. “Either way, the implications for people’s role in hunting extinction are the same,” he said.
Miller insists size matters. He believes the molecular evidence that people killed a bird as large as the Genyornis has implications for the story of the disappearance of megafauna around the world..
Although some scientists continue to believe that a cold snap around 12,000 years ago wiped out the giants of the northern hemisphere, the hypothesis that they were driven to death is largely supported. North American paleontologists have identified sites where early inhabitants slaughtered mastodons and mammoths, lending credence to this theory.
Miller himself has uncovered evidence that early Australians were chasing Genyornis: hundreds of his shell fragments are blackened, with distinct hot spots as if they had been thrown into a campfire after being cooked. An egg burned in a forest fire, an obvious alternative explanation, would look different.
If more primitive peoples on this continent killed off the huge animals that surrounded them around 45,000 years ago, he explains, “then it’s even more likely that the humans of 11,000 years ago could have do the same in the Americas”.