Fifty thousand years ago, Australia was populated by big birds, really big birds. One of them, known as mihirunga, or “thunder bird”, was six times the size of a modern emu; he may have weighed 250 kilograms and was over 2 meters tall. But the giant Genyornis newtoni disappeared 45,000 years ago, and researchers have long wondered whether the culprits were human hunters or climate change. Now, a new analysis of ancient eggshells – leftovers from a prehistoric holiday – suggests that “humans were responsible,” says Trevor Worthy, a paleozoologist at Flinders University.
People arrived in Australia about 55,000 years ago; from 45,000 years ago, the Genyornis the bird was extinct, along with dozens of other giant species, including marsupial lions and giant kangaroos. But the evidence linking their extinction to the arrival of humans was circumstantial at best. Although North American peoples left clear evidence of the hunting and slaughter of large animals – bone with cut marks or stone bullet points embedded in mammoth remains, for example – none of this existed in Australia.
A possible smoking gun appeared in 2016, when researchers linked burnt eggshells at sites near Australia’s southern and western coasts to Genyornis. At the time, they argued that the shells were evidence of omelette making on a scale large enough to push the thunder bird over the edge. “Much [of shells] it had been burned, which implies human consumption, “says Gifford Miller, a geoscientist at the University of Colorado, Boulder, and co-author of the article.” It would have been the first sure evidence of direct predation. “
But other researchers have argued that the shell pieces were too small and thin to belong Genyornisand suggested they belonged Megapodium, a genus of smaller birds distantly related to chickens and turkeys. To prove that the eggs, the size of an emu or a small ostrich egg, belonged Genyornis“We needed an independent way to prove that the shells belonged to a giant bird,” says Miller.
The team tried to extract ancient DNA from the fossilized shells, but their efforts were in vain. “The shells were too old and the climate is too hot,” says University of Turin proteomics expert Beatrice Demarchi, who worked with Miller to identify egg shells. Instead, the team turned to eggshell proteins.
Eggshells form rapidly, within 24 hours within the bird’s oviduct, and readily trap proteins within the calcium and mineral crystals that form the shell. These proteins “are not affected by contamination from the environment, only by temperature and time,” says Demarchi. She was able to recover remnants of egg-forming proteins.
When the team compared the protein sequences to those found in modern megapod eggs, they were completely different, even outside the group that connects all living land birds, Demarchi says. That remained Genyornisthought to be a distant relative of the duck as the only possibility, the researchers write this week in Proceedings of the National Academy of Sciences.
Worthy, who opposed previous analyzes that tied egg shells to Genyornis and was not involved in the research, he says he was impressed with the results. “They handled the challenge quite well: the protein evidence seems strong enough,” he says.
But thanks to scant skeletal evidence, the mysteries remain: why would such a large bird lay relatively small, thin-shelled eggs? “If they’re right, we have a very large bird with the smallest known eggs for a bird with its mass,” says Worthy. What we may need to solidify that connection is an eggshell next to a series of thunderbird remains, she says.
The burnt shells suggest that the first humans to arrive in Australia were stealing and eating eggs, each of which would have been a family-friendly meal, rather than facing the large birds directly. “It’s entirely possible that humans managed to chase the birds out of the nest,” says Miller. “The most effective way to cause extinction is to capture the young.”