Proteins isolated from prehistoric eggshell fragments discovered in Australian sands reveal that the continent’s first humans ate the eggs of a two-meter tall bird that went extinct about 47,000 years ago.
The discovery of burn scars on old shell scraps some years ago showed that the early Australians cooked and ate huge eggs laid by a long-extinct bird, sparking a passionate discussion about the species that deposited them.
By comparing protein sequences from powdered egg fossils to those encoded in the genomes of contemporary avian species, an international team led by experts from the universities of Cambridge and Turin has put the animal on the evolutionary tree.
“Time, temperature and the chemistry of a fossil all dictate how much information we can glean,” said senior co-author Prof Matthew Collins from the University of Cambridge’s Department of Archaeology.
“Eggshells are made of mineral crystals that can tightly trap some proteins, preserving this biological data in the harshest of environments potentially for millions of years.”
The ancient eggs were from Genyornis, a large flightless “mihirung” or “Thunder Bird” with tiny wings and massive legs that roamed prehistoric Australia in swarms, according to studies published in the journal Proceedings of the National Academy of Sciences.
Genyornis stood over two metres tall, weighed between 220-240 kilos, and produced 1.5 kilogram melon-sized eggs, according to fossil records. It was one of the “mega-fauna” of Australia that died out a few thousand years after humans arrived, implying that humans played a role in its extinction.
Humans first arrived in Australia 65,000 years ago, according to the most “robust” evidence. Burnt eggshells from the previously unknown species all date to roughly 50 to 55 thousand years ago, not long after Genyornis went extinct and humans had spread throughout most of the continent.
“There is no evidence of Genyornis butchery in the archaeological record. However, eggshell fragments with unique burn patterns consistent with human activity have been found at different places across the continent,” said senior co-author Prof Gifford Miller from the University of Colorado.
“This implies that the first humans did not necessarily hunt these enormous birds, but did routinely raid nests and steal their giant eggs for food,” he said. “Overexploitation of the eggs by humans may well have contributed to Genyornis extinction.”
The Progura was related to today’s megapodes, a group of birds in the galliform lineage, which also contains ground-feeders such as chickens and turkeys. We found that the bird responsible for the mystery eggs emerged prior to the galliform lineage, enabling us to rule out the Progura hypothesis. This supports the implication that the eggs eaten by early Australians were laid by Genyornis.
Prof Beatrice Demarchi
While Genyornis was always a contender for the mystery egg layer, other experts claimed that the Progura or ‘giant malleefowl,’ a smaller extinct bird weighing roughly 5-7 kg and equivalent to a large turkey, was a more likely candidate according to shell shape and thickness.
The original plan was to settle the debate by extracting ancient DNA from shell fragments, but the genetic material had not survived the harsh Australian climate.
Miller enlisted the help of Cambridge and Turin scientists to investigate a relatively new method for extracting a different form of “biomolecule”: protein.
Using a massive new collection of biological material called the Bird 10,000 Genomes (B10K) project, the scientists were able to compare the sequences in ancient proteins to those of living species, despite the lack of hereditary data.
“The Progura was related to today’s megapodes, a group of birds in the galliform lineage, which also contains ground-feeders such as chickens and turkeys,” said study first author Prof Beatrice Demarchi from the University of Turin.
“We found that the bird responsible for the mystery eggs emerged prior to the galliform lineage, enabling us to rule out the Progura hypothesis. This supports the implication that the eggs eaten by early Australians were laid by Genyornis.”
Prof Miller has previously shown that comparable charred shells may be discovered at hundreds of sites throughout the far western Ningaloo coast. The 50,000-year-old eggshell evaluated for the study originated from the archaeological site of Wood Point in South Australia.
The researchers point out that the earliest Australians’ Genyornis egg exploitation behavior is likely similar to that of early humans with ostrich eggs, whose shells have been discovered at archaeological sites across Africa reaching back at least 100,000 years.
Prof Collins added: “While ostriches and humans have co-existed throughout prehistory, the levels of exploitation of Genyornis eggs by early Australians may have ultimately proved more than the reproductive strategies of these extraordinary birds could bear.”
