Elephant birds were large, flightless birds that lived on the island of Madagascar. They are now extinct, meaning they no longer exist. Scientists believe they disappeared around the year 1000 AD, probably because of human activities. There are three known species of elephant birds: one is in the group Mullerornis, and two are in the group Aepyornis. Aepyornis maximus might have been the largest bird ever, with eggs that were the biggest known for any amniote. These birds ate plants and were important parts of Madagascar's ecosystems before humans arrived. Elephant birds are a type of bird called palaeognaths, which include flightless birds like ostriches. Their closest living relatives are kiwi birds, found only in New Zealand. This suggests that flightless birds like kiwi and elephant birds evolved to lose their ability to fly independently, not because their ancestors were separated when the landmass Gondwana broke apart.

Discovery

Elephant birds have been extinct since at least the 17th century. Étienne de Flacourt, a French governor of Madagascar during the 1640s and 1650s, wrote about a bird called the Vouron patra, which resembled an ostrich. Many believe this refers to elephant birds, though some argue Flacourt may have repeated stories from earlier times. In his 1658 book, Histoire de la grande isle Madagascar, Flacourt described the bird (translated):

Some people in the late 1800s thought the giant bird called the roc, from Marco Polo’s stories, might have been based on elephant birds. However, this idea is not widely accepted.

Between 1830 and 1840, European travelers in Madagascar saw large bird eggs and eggshells. British scientists were more likely to believe reports of giant birds and eggs because they knew about the moa, a large bird from New Zealand. In 1851, the genus Aepyornis and species A. maximus were officially described by Isidore Geoffroy Saint-Hilaire, based on bones and eggs found on the island. This discovery received much attention in newspapers of the time, especially because of the unusually large eggs. By 1890, the name "elephant bird" was commonly used in English to describe Aepyornis. In 1894, the genus Mullerornis was introduced by Alphonse Milne-Edwards and Alfred Grandidier.

Two whole eggs were found in southern Western Australia, one in the 1930s (the Scott River egg) and another in 1992 (the Cervantes egg). Both were identified as Aepyornis maximus, not Genyornis newtoni, a different extinct bird from Australia. Scientists think the eggs may have traveled from Madagascar to Australia via the Antarctic Circumpolar Current. Evidence for this includes the discovery of penguin eggs on Western Australia’s shore that may have come from the Kerguelen Islands, and an ostrich egg found floating in the Timor Sea in the 1990s.

Taxonomy and evolution

Elephant birds, like ostriches, rheas, cassowaries, emus, kiwis, and the extinct moa, are ratites and belong to the infraclass Palaeognathae. They could not fly, and their breast bones lacked a keel.

Ancient DNA from elephant bird remains, including eggs, and genetic studies of other palaeognaths show that New Zealand kiwis are the closest known relatives of elephant birds. However, kiwis and elephant birds diverged from each other about 54 million years ago during the early Eocene epoch.

Elephant birds are placed within Palaeognathae in the following order:
– Struthionidae (ostriches)
– † Dinornithiformes (moa)
– † Aepyornithiformes (elephant birds)
– Casuariiformes (emu, cassowary)

Historically, scientists believed that the ancestor of ratites was flightless and lived on Gondwana before it broke apart. They thought ratites evolved separately as Gondwana split during the Cretaceous. However, genetic evidence, such as the flighted tinamou being part of the ratites, now suggests that ratites, including elephant birds, developed flightlessness multiple times after Gondwana broke apart.

Madagascar has very few Cenozoic terrestrial fossils, with almost no records from the end of the Cretaceous (around 66 million years ago) until about 80,000 years ago. This makes the arrival and evolution of elephant birds on Madagascar largely unknown. Complete mitochondrial genomes from elephant bird eggshells show that Aepyornis and Mullerornis are genetically distinct. Molecular clock analyses estimate their ancestors split around 27–30 million years ago during the Oligocene epoch.

Some extinct birds, like Eremopezus and Stromeria from Egypt, were once grouped with elephant birds but are now considered unrelated. Eggshell fragments from the Canary Islands, dating to the early Pliocene (around 4 million years ago), have been linked to elephant bird relatives based on pore shape, though recent research suggests they likely belong to ostriches.

All elephant birds are typically placed in the family Aepyornithidae, named by Bonaparte in 1853. Some scientists, however, suggest Aepyornis and Mullerornis should be in separate families within Aepyornithiformes, with Mullerornis in Mullerornithidae, named by Lamberton in 1934. The order Aepyornithiformes is traditionally credited to Newton in 1884, based on his use of "Aepyornithes" in the 9th edition of the Encyclopædia Britannica. Newton used the term earlier in 1877. The first use of "Aepyornithiformes" was by Max Fürbringer in 1888.

At least 11 species of Aepyornis have been named, but many are disputed. Some scientists consider all Aepyornis species as one, A. maximus. Up to three species of Mullerornis have been described. A 2018 study by Hansford and Turvey identified four valid elephant bird species: A. maximus, A. hildebrandti, Mullerornis modestus, and a new species, Vorombe titan. However, genetic data later cast doubt on Vorombe titan, as eggshell DNA and skeletal remains from Vorombe were found to belong to the same genetic group as A. maximus. Some researchers suggest Vorombe specimens may represent large females of A. maximus, similar to the sexual dimorphism seen in the giant moa genus Dinornis.

Eggshells from northern Madagascar, with distinct DNA, may represent a third Aepyornis species, but the lack of skeletal remains from the region makes this uncertain. These could instead be a genetically distinct subpopulation of A. hildebrandti.

• Order Aepyornithiformes: Authority traditionally given as (Newton 1884)
• Genus Aepyornis (Geoffroy Saint-Hilaire 1850) (Synonym: Vorombe Hansford & Turvey 2018)
• Aepyornis hildebrandti (Burckhardt, 1893)
• Aepyornis maximus (Hilaire, 1851)
• Genus Mullerornis (Milne-Edwards & Grandidier 1894)
• Mullerornis modestus (Milne-Edwards & Grandidier 1869)
• Hansford & Turvey 2018

Description

Elephant birds were large birds, with the tallest reaching 3 metres (9.8 ft) when standing upright. Like other ratites, they had long legs and long necks, with small heads compared to their body size. Their skulls had straight, thick, cone-shaped beaks that were not curved. The skulls of different elephant bird species are similar in shape but vary in size. The front part of the skull in Mulleronis is less strong than in Aepyornis. Marks on the top of the skulls may have been places where fleshy structures or feathers attached. Their wings were very small and not used for flying. The spine likely had 24 separate vertebrae, with 16-17 in the neck and 6-7 in the chest area. The pelvis in Aepyornis was strong, with its parts (pubis, ilium, and vertebrae) tightly connected. The pelvis in Mulleronis was three times wider than it was long. The bones in the hind legs, especially the femur and tibiotarsus, were thick and strong in Aepyornis, with the femur being short and wide. In Mullerornis, these bones were slightly thinner and less strong. The bones at the end of the feet that held claws were not curved and were broad, though slightly longer and sharper in Mullerornis.

Mullerornis was the smallest elephant bird, weighing about 80 kilograms (180 lb), with a skeleton less strong than Aepyornis. A. hildebrandti likely weighed around 230–285 kg (507–628 lb). Aepyornis maximus is estimated to have weighed between 275 kg (606 lb) and 700–1,000 kg (1,500–2,200 lb), making it one of the largest birds ever, along with Dromornis stirtoni and Pachystruthio dmanisensis. Female A. maximus were likely larger than males, as seen in other ratites.

Biology

Studies of brain endocasts show that both A. maximus and A. hildebrandti had much smaller optic lobes (brain parts that process vision) than most other ratites. These brain structures are similar to those of kiwis, their closest living relatives, and suggest a lifestyle active at night. The optic lobes of Mullerornis were also reduced, but less so, which may indicate a lifestyle active during night or twilight. A. maximus had larger olfactory bulbs (brain parts that help with smell) than A. hildebrandti, suggesting that A. maximus lived in forested areas where smell was more useful, while A. hildebrandti lived in open areas. Elephant birds likely relied heavily on their sense of smell. Analysis of their ear structures suggests they had poor hearing. Based on the shape of their leg bones, elephant birds likely walked slowly, similar to moas, unlike most living ratites like ostriches, emus, and rheas. Smaller Mullerornis may have been slightly more agile than larger Aepyornis species.

Elephant birds are believed to have been herbivores and played a major role in Madagascar’s pre-human plant-eating animals. A 2022 study using isotope analysis found that some A. hildebrandti specimens had diets with about 48% grass, similar to the living Rhea americana, suggesting they lived in open areas. Other species, like A. maximus and Mullerornis modestus, likely ate plants in forests. Some evidence suggests Aepyornis may have stood upright on its legs to reach higher plants. Certain Malagasy palm fruits, such as those of the threatened Voanioala gerardii, may have evolved to be eaten by elephant birds, allowing seeds to survive digestion. Similar fruits in New Guinea are eaten by cassowaries, which help spread the seeds. Other plants, like Erythrina hazomboay and Tabernaemontana stellata, may have evolved to attract elephant birds with their seeds. Plants in the Uncarina genus may have evolved to stick to elephant bird feet. Many Malagasy shrubs and young trees have traits like wide branching and flexible stems, which may help them resist damage from elephant bird feeding. Similar traits in New Zealand plants are thought to help resist damage from moas.

Elephant birds are believed to have grown slowly, taking many years to reach full size, unlike most birds that grow to full size in about a year. They likely grew in short bursts rather than continuously. An embryo of Aepyornis found in an egg that died near the end of incubation shows a strong, robust skeleton even at an early stage, suggesting hatchlings were likely able to move and care for themselves quickly.

The eggs of Aepyornis are the largest known among amniotes (animals with watertight eggs). They measure about 5.6–13 liters in volume, 26–40 centimeters in length, and 19–25 centimeters in width. The thickest eggs are about 3.3 millimeters thick and weigh around 10.5 kilograms. Eggs of Mullerornis were much smaller, averaging 1.1 millimeters thick and weighing about 0.86 kilograms. The large size of Aepyornis eggs suggests they required a lot of calcium, which female birds typically get from a special bone tissue in their legs. Evidence of this tissue has been found in the leg bones of A. maximus.

Extinction

It is widely believed that the extinction of elephant birds was caused by human activity. These birds were once found all over Madagascar, from the northern to the southern tip of the island. During the late Holocene, many other animals in Madagascar also went extinct, including several species of Malagasy hippopotamus, two types of giant tortoise (Aldabrachelys abrupta and Aldabrachelys grandidieri), the giant fossa, more than a dozen species of giant lemurs, the aardvark-like animal Plesiorycteropus, and the crocodile Voay. Some elephant bird bones with cuts have been dated to about 10,000 BC. Some scientists think these cuts may show that humans and elephant birds lived together for a long time. However, this idea conflicts with other evidence that suggests humans arrived on the island much later, around the mid-first millennium AD.

A 2021 study suggested that elephant birds, along with Malagasy hippopotamus species, became extinct between 800–1050 AD (1150–900 years before present), based on the latest scientific dating methods. The timing of these dates matches major changes in Madagascar’s environment caused by humans, such as turning forests into grasslands, likely for raising cattle. This environmental change may have made it easier for humans to find elephant birds, though there is little evidence that humans hunted them. Some evidence suggests humans may have used elephant bird eggs. Introduced diseases have been proposed as a possible cause of extinction, but this idea is less likely because humans and elephant birds lived together on the island for centuries.