Eggshells – not bones – reveal the existence of previously unknown extinct birds

A previously unknown species of elephant bird was recently discovered in northeastern Madagascar and was identified only from its ancient eggshells.

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More than 1,200 years ago, the island of Madagascar was home to an amazing collection of flightless, ostrich-like birds that stood over three meters (9-10 feet) tall, weighed around 2,200 pounds and laid eggs over bigger than a soccer ball. These magnificent giants were known as elephant birds. Today, all that remains of these birds are a few scattered bones and eggshell fragments – and many unanswered questions. Questions like: how many species were there? What were these giant birds eating? Do they have living relatives?

An international team of researchers published a new study (ref) recently, announcing the discovery of another distinct lineage of elephant bird. But surprisingly, this remarkable discovery was not the result of the discovery of a skeleton, or even of some bones: it was based uniquely on DNA extracted from some scattered eggshell fragments that scientists had spent years collecting in the northeast part of the island.

“This is the first time that a taxonomic identification has been derived from an elephant bird eggshell and it opens up a field that no one would have thought of before,” said the study’s co-author, geologist Gifford Miller, eminent professor of geological sciences and faculty member. at the Institute of Arctic and Alpine Research at the University of Colorado at Boulder. One of Professor Miller’s many areas of expertise is the study of ancient eggshells in Australia and around the world.

“Perhaps this is another way of looking back and asking, ‘Was there more diversity in birds than we think?’ thought Professor Miller.

This pioneering discovery is significant because bird bones are delicate and usually do not last long. Identifying a new species of bird from its ancient eggshell fragments can allow scientists to learn more about the diversity of birds that once roamed the planet.

Elephant birds are a product of their unique island environment and geological history. Madagascar is a large island that separated from the Indian subcontinent around 90 million years ago and from Africa at least 60 million years ago. Since these events, Madagascar has remained separated from all landmasses by deep ocean waters. This long isolation has allowed plants and animals to follow their own evolutionary paths, so almost all of the island’s biodiversity is unique and found nowhere else on the planet.

Then people arrived. Madagascar was initially settled by Austronesian peoples, who probably arrived from Indonesia around 2,000 years ago, later followed by Bantus from East Africa and others. When these people arrived, they were probably terrified of Madagascar’s largest land animal: Aepyornis, Or purple in the Malagasy language, an imposing bird weighing as much as a rhinoceros and equipped with a sharp beak and deadly unadorned talons. Similar to the ostrich of Africa, the rhea of ​​South America, the emu and cassowary of Australia, and the moa and kiwi of New Zealand, the elephants of Madagascar were flightless. And yet, elephant birds were so impressive that they may have inspired rock myths, or Rukh, a gigantic flying bird said to carry off elephants and other large animals to eat.

Lead author of the recent study, Alicia Grealy, now based at CSIRO, conducted this research as part of her doctoral dissertation at Curtin University. To carry out this research, she and her collaborators collected more than 960 eggshell fragments from 291 localities in southern, central and, for the first time, northern Madagascar (Figure 1a). Radiocarbon dates indicate that the collected eggshells were between 1290 and 6190 years old, and they are contemporary with most radiocarbon-dated bone specimens from these regions.

Measurements of eggshell fragment thicknesses revealed three distinct morphotypes: in the dry southern part of the island, two distinct eggshell thicknesses were measured (Figure 1b). Eggshells collected from the swampy and forested regions of northern Madagascar had an intermediate thickness between the two southern eggshell morphotypes.

Extrapolating from the measured eggshell thicknesses and the corresponding masses of the bird species that produced them, the team estimated that the mass of elephant birds producing the thinnest eggshells would have been emu-sized birds with a mass of around 41 kg (90 lb), while the thickest eggshells are said to have been laid by birds weighing around 1,000 kg (2,205 lb). Based on these same methods, the intermediate-thickness eggshells were likely laid by intermediate-sized birds that the team estimated to weigh around 230 kg (507 lb).

Dr. Grealy then extracted ancient DNA (aDNA) and protein molecules from eggshells of each morphotype and recovered mitochondrial genomes from three elephant birds. Dr. Grealy discovered that ancient mitochondrial DNA was sealed so tightly in eggshells that she estimated it could probably survive relatively intact for 10,000 years.

After analyzing aDNA and protein sequences from ancient eggshells, Dr. Grealy and his collaborators concluded that the family tree of elephant birds, originally thought to include 16 species, only included actually only three sexually dimorphic species, where the females were about twice as large as the males. They also confirmed an earlier discovery that elephant birds are most closely related to the flightless chicken-sized kiwi bird – a discovery that changed our view of avian evolution.

The efforts of Dr. Grealy and his collaborators created a new collection of eggshells from elephant birds found in the far north of Madagascar, which they believe were genetically distinct from other eggshells. elephant bird eggs. Thus, they concluded that these Norse eggshells represent a new species of Aepyornis elephant bird, whose skeletal fossils still await discovery pending concerted research.

“The molecules preserved in some of these eggshells allowed us to discover a potentially new species that lived in the upper country,” Dr Grealy said.

The researchers concluded that the elephant birds were, despite their terrifying sizes, vegetarians.

“We were also able to determine that different species ate a mix of grasses, shrubs and succulents,” Dr Grealy explained.

Finally, Dr. Grealy and his team found that extreme gigantism was a relatively recent evolutionary development in elephant birds – and was likely due to climate change that led to the expansion of grasslands in the Pleistocene.

“Another startling finding is that the gigantic size of the largest elephant birds (Aepyornis the largest) probably appeared during the last 1.4 million years, in parallel with the evolution of the environment and the ecosystem in Madagascar”, asserted Dr Grealy. “This species has almost doubled in size over a very rapid and recent period.”

“It’s amazing to think that these thousand-year-old egg fragments can give us insight into where elephant birds lived, what they ate, what their ancestors looked like, and how they changed over the years. “, commented Dr. Grealy.

“The findings contribute to our understanding of how elephant birds lived and functioned in Madagascar’s unique ecosystems, and also reinforce how ancient eggshell DNA is a promising avenue for studying evolution and evolution. extinction of giant animals,” explained Dr Grealy.

“There is surprisingly much to discover from the eggshell.”

Source:

Alicia Grealy, Gifford H. Miller, Matthew J. Phillips, Simon J. Clarke, Marilyn Fogel, Diana Patalwala, Paul Rigby, Alysia Hubbard, Beatrice Demarchi, Matthew Collins, Meaghan Mackie, Jorune Sakalauskaite, Josefin Stiller, Julia A. Clarke, Lucas J. Legendre, Kristina Douglass, James Hansford, James Haile and Michael Bunce (2023). Molecular exploration of fossil eggshell reveals hidden lineage of extinct giant bird, Nature Communication 14:914 | doi:10.1038/s41467-023-36405-3

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