Picture an omelette made from 150 hen's eggs. It might be larger than your table! But by some counts, a single egg from an elephant bird in Madagascar could hold at least that much. That might be the largest ever, but a dinosaur laid a longer one, and there's no clear way to compare the volumes of the two (yet!).
A giant bird of Madagascar that became extinct about 1,000 years ago. Guinness says its eggs beat every known dinosaur egg.
A stretched-out egg: about three times as long as it is wide. The two best-preserved eggs are 40–45 cm16–18 in long, and some are reported at 61 cm24 in.
Longest: the dinosaur egg. Most inside, by Guinness's count: the elephant bird.
Longest and biggest aren't the same thing. The dinosaur egg wins on length, with eggs reported up to 61 cm24 in, but the two best-preserved were only about 150 mm5.9 in across. The elephant bird egg is shorter, at up to 33 cm13 in, yet Guinness says it was bigger than any known dinosaur egg. We found no one who has measured both volumes the same way.
How many hen's eggs fit inside? Guinness gives the elephant bird egg a capacity of 8.5 L2.2 gal, which it puts at the equivalent of 150 to 180 hen's eggs. National Geographic says that by some estimates it was 120. We couldn't find why the figures differ.
Not every elephant bird was alike. A 2018 study found three kinds of elephant bird skeleton. The largest, Vorombe titan, weighed almost 650 kg1,400 lb, and the name Aepyornis belongs to the medium-sized kind. Eggshell fragments from dunes and archaeological sites are typically not found with skeletons, so tying an egg to a kind is hard.
Elephant bird photo: Brianj996b, CC BY 4.0, via Wikimedia Commons · Giant dinosaur egg photo: Gary Todd, CC0 1.0, via Wikimedia Commons