The world's largest living bird--the ostrich--lays the heaviest egg and she lays six to eight of them while she's at it. Each is about six inches long and weighs up to 2½ pounds. That's 24 chicken eggs in volume. The shell is 0.06 of an inch thick (the diameter of a pinhead) but can support the weight of an adult human. The largest ostrich egg on record was laid in 1988 on a collective farm in Israel. It weighted 5 lb. 2 oz. The extinct giant Elephant Bird (Aephornis maximus) of Madagascar laid eggs as big in volume as seven ostrich eggs and bigger than any dinosaur egg. They were the largest single-cells that ever existed on Earth. By the way, the half-ton Elephant Bird became extinct fairly recently: about 1700. The figure shows eggs of various modern reptiles and birds: Clockwise from the upper-left: an ostrich egg, crocodile eggs, one set of tortoise eggs, another set of tortoise eggs, and an Elephant Bird egg. All based on the same scale: a 6-inch long ostrich egg.