The genus had two species, the smaller A. hildebrandti and the larger A. maximus, which is possibly the largest bird ever to have lived.

[6] However, later DNA studies found that Vorombe titan was indistinguishable from A. maximus, and probably represented large females of the species.

[2] Like the cassowaries, ostriches, rheas, emu and kiwis, the Elephant bird was a ratite; it could not fly, and its breast bone had no keel.

Because Madagascar and Africa separated before the ratite lineage arose,[7] Aepyornis and other elephant birds are thought to have dispersed and become flightless and gigantic in situ.

[8] More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are the New Zealand kiwis, from which they were estimated to have diverged over 50 million years ago.

[13] A 2022 isotope analysis study suggested that individuals of Aepyornis hildebrandti from central Madagascar were mixed feeders that had a large (~48%) grazing component to its diet, similar to that of the living Rhea americana, while A. maximus was probably a browser.

A recent archaeological study found fragments of eggshells among the remains of human fires,[17] suggesting that the eggs regularly provided meals for entire families.

The exact time period when they died out is also not certain; tales of these giant birds may have persisted for centuries in folk memory.

[18][19][20] After many years of failed attempts, DNA molecules of Aepyornis eggs were successfully extracted by a group of international researchers and results were published in 2010 in the Proceedings of the Royal Society B.

The bones of these domesticated fowl have been found in subfossil sites on the island (MacPhee and Marx, 1997: 188), such as Ambolisatra (Madagascar), where Mullerornis modestus and A. maximus have been reported.