Although many people assume immense dinosaurs must have had huge eggs, the largest known eggs were actually laid by the flightless elephant bird, Aepyornis. Elephant birds were up to 3 meters (10’) tall and weighed as much as 500 kilograms (1100 lbs.). They were ratites, flightless birds whose closest living relatives are the kiwi birds of New Zealand. This suggests the ancestors of elephant birds came to Madagascar from the Australian region and only became flightless and giant after their arrival. Based on the relative sizes of its nostrils and eye orbits, Aepyornis may have been nocturnal like its kiwi cousins. Aepyornis appears to have evolved in relative seclusion on the microcontinent of Madagascar with few natural predators. Their numbers may have plummeted after humans arrived in force, although a 2018 discovery of butchered Aepyornis bones suggests some humans may have arrived in Madagascar earlier than previously thought. While evidence of butchered bones is limited, Aepyornis eggshell fragments are commonly found in campfires at archaeological sites and egg predation may have doomed the species.
The last Aepyornis probably died around 1,000 years ago and reports of the bird may have been the source for Marco Polo’s 1298 account of the mythical roc, a bird large enough to feed on elephants. However, an unconfirmed sighting was reported in 1658, over a century and a half after Europeans began exploring the Americas.
Aepyornis eggs are not only the largest known eggs in the fossil record but may represent the largest possible egg for a terrestrial animal. This is because there is a limit as to how thick eggshells can be and yet still allow developing embryos to break through the shell to hatch. The strength of Elephant bird eggshells is attested to by innumerable thousands of Elephant bird eggshell fragments that still line beaches on the southern tip of Madagascar, centuries after the last known Aepyornis ventured out on a nocturnal stroll.