Étienne de Flacourt, a French governor of Madagascar during the 1640s and 1650s, mentioned an ostrich-like bird, said to inhabit unpopulated regions, although it is unclear whether he was repeating folk tales from generations earlier.

"[2][3] There has been speculation, especially popular in the latter half of the 19th century, that the legendary roc from the accounts of Marco Polo was ultimately based on elephant birds, but this is disputed.

[5] Like the ostrich, rhea, cassowary, emu, kiwi and extinct moa, elephant birds were ratites; they could not fly, and their breast bones had no keel.

Because Madagascar and Africa separated before the ratite lineage arose,[6] elephant birds are thought to have dispersed and become flightless and gigantic in situ.

[7] More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are New Zealand kiwi,[8] though the split between the two groups is deep, with the two lineages being estimated to have diverged from each other around 54 million years ago.

[12] Complete mitochondrial genomes obtained from elephant birds eggshells suggest that Aepyornis and Mullerornis are significantly genetically divergent from each other, with a molecular clock analysis estimating the split around 27 million years ago.

[9] Molecular dating estimates that the divergence between Aepyornithidae and Mullerornithidae occurred approximately 30 Ma, close to the Eocene-Oligocene boundary, a period of marked global cooling and faunal turnover in the Northern Hemisphere.

The tops of elephant bird skulls display punctuated marks, which may have been attachment sites for fleshy structures or head feathers.

[23] A 2022 isotope analysis study suggested that some specimens of Aepyornis hildebrandti were mixed feeders that had a large (~48%) grazing component to their diets, similar to that of the living Rhea americana, while the other species (A. maximus, Mullerornis modestus) were probably browsers.

[25] Several elephant bird bones with incisions have been dated to approximately 10,000 BC which some authors suggest are cut marks, which have been proposed as evidence of a long history of coexistence between elephant birds and humans;[29] however, these conclusions conflict with more commonly accepted evidence of a much shorter history of human presence on the island and remain controversial.

[30] A 2021 study suggested that elephant birds, along with the Malagasy hippopotamus species, became extinct in the interval 800–1050 AD (1150–900 years Before Present), based on the timing of the latest radiocarbon dates.

Introduced diseases (hyperdisease) have been proposed as a cause of extinction, but the plausibility for this is weakened due to the evidence of centuries of overlap between humans and elephant birds on Madagascar.