Aepyornis is a group of elephant birds that no longer exists. These birds were once only found in Madagascar. The group had two types: the smaller A. hildebrandti and the larger A. maximus. A. maximus might have been the biggest bird ever. The New Zealand kiwi is their closest living relative. They became extinct around the year 1000 AD. This probably happened because of human activities.

Taxonomy

Brodkorb (1963) said there were four types of Aepyornis: A. hildebrandti, A. gracilis, A. medius, and A. maximus. However, Hume and Walters (2012) said only one type, A. maximus, was valid. Most recently, Hansford and Turvey (2018) said only A. hildebrandti and A. maximus were valid.

• Aepyornis grandidieri Rowley 1867 (questionable name)
• Aepyornis hildebrandti Burckhardt, 1893; Aepyornis gracilis Monnier, 1913; Aepyornis lentus Milne-Edwards & Grandidier, 1894; Aepyornis minimus; Aepyornis mulleri Milne-Edwards & Grandidier, 1894
• Aepyornis maximus Hilaire, 1851; Aepyornis cursor Milne-Edwards & Grandidier, 1894; Aepyornis intermedius; Aepyornis medius Milne-Edwards & Grandidier, 1866; Vorombe titan (Andrews 1894) Hansford & Turvey 2018

The main type, Aepyornis titan Andrews, 1894, was moved to a different group called Vorombe by Hansford and Turvey (2018). A. ingens is a name that means the same as A. titan. Aepyornis grandidieri Rowley, 1867, is a name that is not certain because it is only known from a piece of an eggshell. Hansford and Turvey (2018) also said Aepyornis modestus is the correct name for all Mullerornis types. Later DNA studies showed that Vorombe titan was the same as A. maximus and likely represented large females of the species.

Like cassowaries, ostriches, rheas, emus, and kiwis, elephant birds were ratites. Ratites could not fly, and their breast bones had no keel. Because Madagascar and Africa separated before ratites evolved, Aepyornis and other elephant birds probably became flightless and large on Madagascar. Recent DNA studies suggest that kiwis are the closest living relatives of elephant birds. Scientists think elephant birds and kiwis separated more than 50 million years ago.

Description

The species of Aepyornis are some of the largest birds. Scientists estimate that A. hildebrandti weighed about 235 kilograms (520 lb), while A. maximus weighed between 275–1,000 kilograms (610–2,200 lb). This makes A. maximus one of the largest, if not the largest bird that ever lived, with a height of about 3 meters (9.8 ft). The head had a straight, thick beak that was larger in A. hildebrandti compared to A. maximus. However, the heads of both birds were small relative to their body size. The neck was long, with 16 to 17 neck bones. The wings were very small and not used for flying. The bones in the pelvis area (including the vertebrae, ilium, and pubis) were tightly joined together, making it hard to tell where one bone ended and another began. The legs were long compared to body size, with strong and thick bones. The femur, in particular, was short and thick. The tibiotarsus had a noticeable ridge for muscles to attach. There is no evidence that these birds had a fourth toe or a spur. The bones at the end of their toes were wide and not curved. In A. maximus, females were likely larger than males, as seen in other ratites.

Ecology

Studying brain endocasts shows that both A. maximus and A. hildebrandti had much smaller optic lobes, like those of kiwis, which are their closest living relatives. This suggests both species likely lived at night, similar to kiwis. A. maximus had larger olfactory bulbs than A. hildebrandti, which may mean A. maximus lived in forests where smell was more helpful, while A. hildebrandti lived in open areas. Elephant birds likely grew in short bursts instead of growing continuously. A 2022 isotope study found that A. hildebrandti from central Madagascar ate both plants and grass, with about 48% of their diet being grass, similar to the living Rhea americana. In contrast, A. maximus probably ate mostly leaves and branches. Isotope analysis of eggshells from A. hildebrandti in northern Madagascar suggests this group likely ate mostly leaves and branches, not a mix of foods.

An embryo of Aepyornis was found inside an intact egg, which was about 80-90% through incubation when the embryo died. This skeleton shows that even at this early stage of development, the bones were very strong, stronger than those of young ostriches or rheas. Aepyornis eggs are the largest known for any amniote, with a volume of about 5.6–13 liters. They were 26–40 centimeters long and 19–25 centimeters wide. These eggs were about 160 times larger in volume than a chicken egg. Because of their large size, elephant bird eggs needed a lot of calcium, which female birds usually get from medullary bone in their thighs. Possible remains of this bone tissue have been found in the thighs of A. maximus.

Extinction

The extinction of Aepyornis likely happened because of human activity after people arrived in Madagascar. These large birds were once found across the entire island, from the north to the south. One idea, called the blitzkrieg hypothesis, suggests that humans hunted the birds so quickly that they disappeared in a short time. Evidence shows that people killed the birds, and their eggs may have been especially at risk. A recent study found pieces of eggshells near human fire remains, indicating that eggs were a regular food source for families.

The exact time when Aepyornis died out is unclear. Stories about these giant birds may have lasted for many years in local traditions. Archaeological findings include a bone from A. maximus, dated to about 120 AD, which shows signs of being cut by humans. Other evidence from shell remains suggests A. maximus lived around 1000 AD. Scientists believe A. maximus is linked to the Malagasy legend of the vorompatra, meaning "bird of open spaces." In 2010, researchers successfully extracted DNA from Aepyornis eggs, and their findings were published in the Proceedings of the Royal Society B.

Some scientists also think the extinction might have been caused indirectly by humans, such as through diseases spread by animals like chickens and guineafowl that people brought to Madagascar. Bones from these domesticated birds have been found in ancient sites on the island, including Ambolisatra, where A. maximus and other species were also present.