Paleontologists from Curtin University and elsewhere have examined ancient fossil eggshells of Madagascar’s extinct elephant birds and found that genetic differences in these gigantic birds, which reached 3 m in height and weighed over 500 kg, were linked to eggshell thickness, location, and diet.
An artist’s impression of elephant birds in their natural habitat, Madagascar. Image credit: Bonnie Koopmans.
“The elephant birds of Madagascar were large, flightless ratites that became extinct around a millennium ago,” said Curtin University researcher Alicia Grealy and her colleagues.
“The relatedness of elephant birds to other birds remained a mystery until several genetic studies discovered that they are sister to New Zealand’s kiwi, revolutionizing our understanding of avian diversification.”
“However, the biodiversity and evolutionary relationships within elephant birds have been uncertain and unstable since they were first described over 150 years ago, as most species are known only from few incomplete Pleistocene-Holocene skeletal remains from south and central Madagascar.”
“About eight species of elephant birds across two genera were generally accepted based on morphological comparison of skeletal fossils, but a recent morphometric re-evaluation of skeletal material reclassified elephant birds into four species across three genera (Aepyornis, Mullerornis and a new genus, Vorombe). However, this revision remains questionable.”
Molecular dated phylogenetic tree showing the mitochondrial relationships between eggshell specimens from northern, central and southern Madagascar. Image credit: Grealy et al., doi: 10.1038/s41467-023-36405-3.
In the study, the authors collected and examined over 960 elephant bird eggshell fragments from 291 localities across southern, central, and, for the first time, northern Madagascar.
The specimens were between 1,290 and (at least) 6,190 years old, and were contemporaneous with most previously dated bone specimens from these areas.
Molecules preserved in some of the eggshells helped the team discover a potentially new sub-species which lived in the top end of the country.
The researchers were also able to determine that different species ate a mixture of grass, shrubs and succulents.
“Another surprising finding is that the gigantic size of the largest elephant birds (Aepyornis maximus) likely arose within the last 1.4 million years, alongside the changing environment and ecosystem in Madagascar,” Dr. Grealy said.
“This species nearly doubled in size over a very rapid and recent time frame.”
The findings are an important leap forward in resolving the complex history of some of the world’s largest ancient birds.
“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,” Dr. Grealy said.
“The findings contribute to our understanding of how elephant birds lived and functioned within Madagascar’s unique ecosystems, and also reinforces how ancient DNA from eggshells is a promising avenue for studying the evolution and extinction of giant animals.”
The study appears online this week in the journal Nature Communications.
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A. Grealy et al. 2023. Molecular exploration of fossil eggshell uncovers hidden lineage of giant extinct bird. Nat Commun 14, 914; doi: 10.1038/s41467-023-36405-3
