Ancient Eggshell Fragments Crack Giant Elephant Bird’s Life Secrets

In a region where skeletal fossils are poorly preserved, old eggshells are opening a window into the evolution, diet and distribution of Madagascar’s extinct birds.

Columbia Climate School
February 28, 2023
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An elephant bird egg of the extinct species Aepyornis maximus reconstructed from fragments in a southwest Madagascar market. (Photo by study coauthor Gifford Miller)

A team of researchers has used DNA and other information extracted from ancient eggshell fragments to provide a rare glimpse into the history of Madagascar’s extinct giant elephant birds. The flightless birds, which are thought to have disappeared about 1,000 years ago, reached three meters (9 feet) in height and weighed more than 500 kilograms, or 1,100 pounds. But despite their spectacular size, scientists have had a hard time tracing their evolution and documenting the existence of different species, in part because of the poor preservation of skeletal remains in the warm, humid climate. Investigations of some 950 eggshell fragments have now filled in some of the picture. The results were just published in the journal Nature Communications.

One surprising finding: While the birds probably trace back many millions of years, the gigantic size of the largest ones (Aepyornis maximus) likely arose within just the last 1.4 million years, alongside the changing environment and ecosystem in Madagascar. This species nearly doubled in size over a very rapid and recent time frame, say the researchers.

Recent analyses by other researchers suggest the birds were divided into four species, including one that may have been even bigger than Aepyornis maximus. But some have called these analyses into question due to a lack of intact fossils. In any case, hunting and other human activities seem to be the cause of their demise centuries ago.

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Large concentrations of fragmented elephant bird eggshells can be found scattered across beaches and sand dunes along the coastline of Madagascar. (Photo by study coauthor Gifford Miller)

Lead author Alicia Grealy, who completed the research at Australia’s Curtin University, said that molecules preserved in some eggshells helped the team discover a potentially new sub-species that lived in the north of the country. They were also able to determine that different species had distinct diets of grass, shrubs or succulents. In addition to DNA, the scientists used stable isotope chemistry and the size and shape of eggshells to reach their conclusions.

“Despite their towering size, Madagascar’s elephant birds are one of the island’s most mysterious now-extinct animals,” said study coauthor Kristina Douglass, and archaeologist at the Columbia Climate School’s Lamont-Doherty Earth Observatory. “Their fossils have historically been [rare] at paleontological and archaeological sites.” Douglass participated in excavations and fieldwork to recover the eggshells in southwest Madagascar.

“It is amazing to think that these thousand-year-old egg fragments can give us insight as to where elephant birds lived, what they ate, how their ancestors might have looked, and how they evolved over the years,” said Grealy. The eggs themselves are thought to have weighed up to 10 kilograms, and occupied the volume of about 150 chicken eggs. Even dinosaurs did not lay eggs this big.

The study reinforces how ancient DNA from eggshells is a promising avenue for studying the evolution and extinction of other giant animals, say the researchers.

The paper was coauthored by some 15 other researchers from Australia and the United States, as well as from Sweden and the United Kingdom.

Adapted from a press release by Curtin University.