Hadrosaur << HAD ruh sawr, >> also called hadrosaurid, was a diverse group of dinosaurs that lived about 97 million to 65 million years ago. Scientists believe hadrosaurs were among the most social of all dinosaurs. The animals probably lived in herds, nested in colonies, and took care of their babies.
Most hadrosaurs grew 25 to 35 feet (7.6 to 11 meters) long and up to 9 feet (2.7 meters) tall at the hip. They may have weighed 3 to 4 tons (2.7 to 3.6 metric tons) or more. Newly hatched hadrosaurs were only about 1 foot (30 centimeters) long. Some scientists think the animals grew fast, taking as little as five years to reach adult size.
Hadrosaurs at one time were nicknamed duckbilled dinosaurs, because they had a broad beak of bone at the front of the mouth that resembled a duck’s bill. However, scientists now think that muscles and cheeks filled in the snout behind the beak, and that hadrosaurs had a smooth snout rather than a flat, ducklike bill.
Hadrosaurs probably walked on all four legs most of the time. But when escaping predators, they raised their forelegs and ran on their two hind legs. Hadrosaurs ate several kinds of plants. They had hundreds of teeth to chew tough leaves.
Many hadrosaurs had elaborate bony crests on top of their heads. Some crests consisted of solid bone. Others were hollow, surrounding air passages. Hollow-crested hadrosaurs could have made honking sounds by exhaling air from their nose through the passages. The crests and the sounds they produced may have helped hadrosaurs attract mates.
See also Dinosaur (Ornithopods); Edmontosaurus; Parasaurolophus.
