Egg shells – not bones – reveal the existence of previously unknown extinct birds

A previously unknown species of elephant bird was recently discovered on the northeast side of Madagascar and identified only by its ancient egg shells

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More than 1200 years ago, the island of Madagascar was home to an amazing collection of flightless ostrich-like birds that stood more than three meters (9-10 feet) tall, weighed around 2200 pounds, and laid eggs larger than a football. 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 did these giant birds eat? Do you have living relatives?

An international team of researchers recently published a new study (ref) announcing the discovery of another, distinct lineage of elephant birds. But surprisingly, this remarkable discovery was not the result of finding a skeleton or even some bones: it was based solely on DNA extracted from some scattered eggshell fragments that the scientists had been collecting for years in the northeastern 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 no one would have thought of before,” said study co-author geologist Gifford Miller, distinguished professor of geology Science and faculty member at the Institute for Arctic and Alpine Studies 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.

“Here might be another way to look back in time and ask, ‘Was there more diversity in birds than we realize?'” Professor Miller mused.

This groundbreaking discovery is important because bird bones are delicate and don’t typically last long. Identifying a new bird species from its ancient eggshell fragments could 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 split from the Indian subcontinent about 90 million years ago and from Africa at least 60 million years ago. Since these events, Madagascar has been separated from all continental landmasses by deep oceanic waters. This long isolation allowed plants and animals to follow their own evolutionary paths, so almost all of the island’s biodiversity is unique and cannot be found anywhere else on the planet.

Then the people came. Madagascar was originally colonized by Austronesian peoples, who probably floated in from Indonesia about 2,000 years ago, followed later by the Bantu of East Africa and others. When these peoples arrived, they were probably afraid of Madagascar’s largest land animal: epyornis, or vorompatra in the Malagasy language, a towering bird weighing as much as a rhinoceros and endowed with a pointed beak and deadly no-nonsense claws. Much like Africa’s ostrich, South America’s rheas, Australia’s emu and cassowary, and New Zealand’s moas and kiwis, Madagascar’s elephant birds were flightless. And yet, elephant birds were so impressive that they may have inspired myths about the roc or rukh, a gigantic flying bird that has a reputation for kidnapping elephants and other large animals to feed.

The lead author of the most recent study, Alicia Grealy, who now works at CSIRO, conducted this research as part of her PhD at Curtin University. For this research, she and her collaborators collected more than 960 eggshell fragments from 291 sites in southern, central and, for the first time, northern Madagascar (Figure 1a). Radiocarbon dates indicate that the eggshells collected were between 1290 and 6190 years old and are contemporaneous with most previously radiocarbon-dated bone samples from these areas.

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

By extrapolating the measured eggshell thickness and the corresponding masses of the bird species that produced them, the team estimated that the mass of elephant birds that produced the thinnest eggshells would have been emu-sized birds with a mass of around 41 kg (90 lbs). The thickest eggshells would have been laid by birds weighing approximately 1000 kg (2205 lbs). Building on the same methods, the medium-thick eggshells were likely laid by medium-sized birds, which the team estimated weighed around 230 kg (507 lbs).

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

After analyzing the aDNA and protein sequences from the old egg shells, Dr. Grealy and her collaborators conclude that the elephant bird family tree, originally thought to include 16 species, actually includes only three sexually dimorphic species, in which females were about twice the size of males. They also confirmed an earlier finding that elephant birds are most closely related to the flightless, chicken-sized kiwi bird – a finding that has changed our view of bird evolution.

The efforts of Dr. Grealy and her collaborators created a new collection of elephant bird eggshells found in the far north of Madagascar, which they found to be genetically distinct from other elephant bird eggshells. From this they concluded that these northern eggshells represent a new species Epyornis Elephant bird whose skeletal fossils are still awaiting discovery pending a concerted search.

“Molecules conserved in some of these eggshells helped us discover a potentially new species that lived up in the country,” explained Dr. Grealy.

The researchers concluded that despite their frightening size, elephant birds were vegetarians.

“We also found that different species ate a mix of grass, shrubs and succulents,” explained Dr. Grealy.

Eventually discovered Dr. Grealy and her team found that extreme gigantism was a relatively recent evolutionary development in elephant birds — and was likely due to climate change driving grassland expansion during the Pleistocene.

“Another surprising finding is that the gigantic size of the largest elephant birds (Aepyornis maximus) probably arose within the last 1.4 million years along with the changing environment and ecosystem in Madagascar,” claimed Dr. Grealy. “This species has almost doubled in size in a very rapid and recent period.”

“It is amazing to think that these thousand-year-old egg fragments can give us a glimpse of where elephant birds lived, what they ate, what their ancestors might have looked like and how they evolved over the years,” commented Dr. Grealy.

“The results add to our understanding of how elephant birds lived and functioned in Madagascar’s unique ecosystems, and also reinforce that ancient DNA from eggshells is a promising avenue to study the evolution and extinction of giant animals,” said Dr. Grealy.

“There’s a surprising amount to discover from eggshells.”


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 & Michael Bunce (2023). Molecular exploration of fossil egg shells reveals hidden ancestry of extinct giant bird, nature communication 14:914 | doi:10.1038/s41467-023-36405-3

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