As far as scientists can tell, all dinosaurs nested and laid eggs. From these eggs, their babies hatched. Hundreds of sites with fossil eggs of different dinosaurs have been found all over the world, including in the United States, France, Mongolia, China, Argentina, and India. The largest dinosaur egg fossil found is about 12 inches (30 centimeters) long and 10 inches (25 centimeters) wide, and may have weighed 15.5 pounds (7.0 kilograms). Scientists think the egg came from a giant, 100 million year old dinosaur called a Hypselosaurus. This is more than twice the size of the eggs of the modern African ostrich, which can lay eggs up to 6 inches (15 centimeters) long and 5 inches (13 centimeters) wide. The smallest fossilized egg found so far came from a Mussaurus; it measures about 1 inch (2.5 centimeters) long.