Human's Appetite For Egg Drove this Giant Australian Birds to Extinction

Enormous birds-massive birds-inhabited Australia fifty thousand years ago. One of them, called mihirunga, or "thunder bird," was six times the size of a contemporary emu, weighing up to 250 kilograms and standing over 2 meters tall.

However, the enormous Genyornis newtoni vanished 45,000 years ago, and scientists debated whether human hunters or climate change were to blame.

According to Trevor Worthy, a paleozoologist at Flinders University, a fresh examination of old eggshells-the remains of a prehistoric feast-suggests "humans were responsible."

Humans vs Birds

About 55,000 years ago, humans arrived in Australia; by 45,000 years ago, the Genyornis bird and hundreds of other giant creatures like marsupial lions and huge kangaroos had become extinct. However, the evidence linking their demise to the introduction of humans was at best speculative. Although evidence of hunting and butchering huge creatures was left in North America-bones with cutmarks, for example, or stone projectile points buried in mammoth remains-none of this was found in Australia.

Researchers connected charred eggshells in Australia's southern and western shores to Genyornis in 2016, providing a probable smoking gun. They claimed that the shells proved omelet production on a big enough scale to put the thunder bird over the edge. Gifford Miller, a geoscientist at the University of Colorado, Boulder, and a co-author of the article says, "A lot [of shells] had been burnt, which suggests human use." "That would have been the first concrete proof of predation."

Others, however, said the shell fragments were too tiny and thin to be Genyornis and instead thought they belonged to Megapodius, a smaller bird species distantly related to chickens and turkeys. "We needed some independent means to establish the shells belonged to a gigantic bird," Miller says of the eggs, which are around the size of an emu or small ostrich egg.

Extracting DNA Samples

The scientists attempted to extract ancient DNA from the petrified shells but were unsuccessful. "The shells were too ancient, and the environment is too hot," explains Beatrice Demarchi of the University of Turin, who helped Miller identify the eggshells. The team instead used eggshell proteins.

Eggshells develop swiftly in the bird's oviduct-within 24 hours-and quickly trap proteins inside the calcium and mineral crystals that make up the shell. These proteins are "unaffected by environmental contamination-only by temperature and time," according to Demarchi. She was able to retrieve protein fragments associated with egg development.

The protein sequences were radically different from those discovered in current megapode eggs, even falling outside the group that binds all extant land birds, according to Demarchi. In the Proceedings of the National Academy of Sciences this week, the researchers write that Genyornis, a distant duck cousin, was the only remaining option.

Worthy, who opposed previous studies linking the eggshells to Genyornis and was not involved in the study, believes the findings are impressive. "They've responded admirably to the challenge-the protein data appears to be fairly solid," he says.

However, puzzles persist due to the lack of skeletal evidence: why would such a large bird lay little, thin-shelled eggs? "If they're accurate," Worthy adds, "we've got an enormous bird with the tiniest eggs known for a bird of its size." He says we might need an eggshell adjacent to a set of thunder bird bones to cement that relationship.

Prehistoric People Eating Prehistoric Eggs

The charred shells indicate that the first people in Australia stole and ate eggs-each of which would have been a family-size meal-rather than directly attacking the large birds. "It's possible that people were effective in driving birds away from their nests," Miller adds. "Capturing the young is the most efficient way to induce extinction."

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