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Man would have contributed to the extinction of an Australian prehistoric bird by consuming its (huge) eggs

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Since his arrival around 65,000 years ago, man has largely contributed to shaping landscapes and ecosystems. Part of the Australian megafauna would even have cohabited with the first Aboriginal people who populated the island-continent. The involvement of man in the extinction of ancient animals is still the subject of great scientific debate today. A new discovery may now put an end to one of the archaeopaleontological debates, thanks to the sequencing of protein biomolecules extracted from fragments of prehistoric eggshells. The results of the new study suggest that humans are indeed involved in the extinction of Genyornis newtoni (a running bird more than two meters high), exploiting and massively consuming their eggs.

Australia is one of the few exceptional places where flora and fauna have evolved differently from elsewhere in the world. It was home to some of the largest birds that have ever existed, including those of the Dromornithidae family, which have roamed the island since the Late Oligocene (25 million years ago).

The largest species could reach three meters in height and weigh up to 600 kilograms. These large birds also had very small wings unable to fly their massive bodies. They probably moved in groups, like emus or ostriches, with their powerful legs.

The famous Genyornis newtoni was one of those giant birds (or mihirung in Aboriginal), extinct about 50,000 years ago, in the Pleistocene. According to the fossil record, this running bird was more than two meters tall and weighed between 220 and 240 kilograms. It therefore laid very large eggs of 1.5 kilograms on average. It was part of the Australian megafauna that disappeared soon after the arrival of man. Which suggests that he could be involved in his disappearance.

Pencil sketch of a Genyornis, by Nobu Tamura. © University of Cambridge

Traces of “kitchen burns”

As previously mentioned, Genyornis newtoni would have disappeared a few thousand years after the arrival of man, suggesting that the latter probably played a role in its extinction. However, many researchers had refuted this hypothesis, because no evidence of human consumption of this large bird had been found.

However, peculiar scorch marks have been discovered on the shells of long-extinct giant birds buried in Australian sand, which may mean that instead of hunting giant birds, early Australians instead used in the nests and would have eaten the cooked eggs.

However, the species of giant bird that actually laid the eggs was still the subject of much debate. Some experts believe that the shape and thickness of the shells more closely matches Progura (Leipoa gallinacea), another extinct megapode, also endemic to the island but much smaller than the genyornis (about five to seven kilograms) — and more like a large turkey.

But according to new research co-led by the University of Cambridge and Turin (in Italy), the dates would correspond more to the genyornis. Man is said to have started to occupy Australia around 65,000 years ago, and the burnt eggshells all date from 50 to 55,000 years ago, shortly after man spread through the continent and a little before the total disappearance of the genyornis.

The eggshell fragments with unique burn patterns, consistent with human activity, have been found in different locations across the continent “, explains Gifford Miller, co-lead author of the new study, published in PNAS, and professor of geological sciences at the University of Colorado. ” Overharvesting of eggs by humans may well have contributed to the extinction of genyornis “, he suggests.

Moreover, this anthropogenic consumption of eggs would be similar to that observed concerning ostrich eggs, whose burnt shells dating back at least 100,000 years have been discovered on archaeological sites in Africa. According to data from the new study, the reproductive strategy of genyornis was not efficient enough to support the exploitation of eggs by humans (unlike ostriches, which have cohabited with humans since prehistoric times).

Biomolecular evidence

The researchers also compared the protein sequences of pulverized eggshell fossils to those encoded in the genomes of modern avian species. Eggshells contain mineral crystals that can trap certain proteins and preserve biological data in the harshest environments — potentially for millions of years. The prehistoric ones tested were 50,000 years old and came from the Wood Point archaeological site in South Australia.

The shell proteins were also studied (instead of the genetic material, which unfortunately has not been preserved well enough). Although less rich in information, these biomolecules could be analyzed thanks to a new database of biological material: the Bird 10,000 Genomes (B10K) project.

Scientists then discovered that the prehistoric eggs were laid by birds that appeared before the galliforms. The proguras, belonging to this line, would then not have been able to lay the eggs. ” We discovered that the bird that laid the mysterious eggs appeared before the galliform lineage, which allows us to rule out the Progura hypothesis. “says Beatrice Demarchi, lead author of the study and professor in the Department of Life Science and Biological Systems at the University of Turin. ” This confirms that the eggs eaten by early Australians were laid by genyornis “, she concludes.

Source: PNAS

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