Elephant birds are extinct flightless birds belonging to the order Aepyornithiformes that were native to the island of Madagascar. They are thought to have become extinct during the late 1st millennium to early 2nd millennium AD, likely as a result of human activity. Elephant birds comprised three species, one in the genus Mullerornis, and two in Aepyornis. Aepyornis maximus is possibly the largest bird to have ever lived, with their eggs being the largest known for any amniote. Elephant birds are palaeognaths (whose flightless representatives are often known as ratites), and their closest living relatives are kiwi (found only in New Zealand), suggesting that ratites did not diversify by vicariance during the breakup of Gondwana but instead convergently evolved flightlessness from ancestors that dispersed more recently by flying.
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, mentioned an ostrich-like bird, said to inhabit unpopulated regions, although it is unclear whether he was repeating folk tales from generations earlier. In 1659, Flacourt wrote of the "vouropatra – a large bird which haunts the Ampatres and lays eggs like the ostriches; so that the people of these places may not take it, it seeks the most lonely places." 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.
Between 1830 and 1840, European travelers in Madagascar saw giant eggs and eggshells. British observers were more willing to believe the accounts of giant birds and eggs because they knew of the moa in New Zealand. In 1851 the genus Aepyornis and species A. maximus were scientifically described in a paper presented to the Paris Academy of Sciences by Isidore Geoffroy Saint-Hilaire, based on bones and eggs recently obtained from the island, which resulted in wide coverage in the popular presses of the time, particularly due to their very large eggs.
Taxonomy and biogeography
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, elephant birds has been thought to have dispersed and become flightless and gigantic in situ.
More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are New Zealand kiwi, 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. The ancestors of elephant birds are thought to have arrived in Madagascar well after Gondwana broke apart. The existence of possible flying palaeognathae in the Miocene such as Proapteryx further supports the view that ratites did not diversify in response to vicariance. Gondwana broke apart in the Cretaceous and their phylogenetic tree does not match the process of continental drift. Madagascar has a notoriously poor Cenozoic terrestrial fossil record, with essentially no fossils between the end of the Cretaceous (Maevarano Formation) and the Late Pleistocene. 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.
Two whole eggs have been found in dune deposits in southern Western Australia, one in the 1930s (the Scott River egg) and one in 1992 (the Cervantes egg); both have been identified as Aepyornis maximus rather than Genyornis newtoni, an extinct giant bird known from the Pleistocene of Australia. It is hypothesized that the eggs floated from Madagascar to Australia on the Antarctic Circumpolar Current. Evidence supporting this is the finding of two fresh penguin eggs that washed ashore on Western Australia but originated in the Kerguelen Islands, and an ostrich egg found floating in the Timor Sea in the early 1990s.