Hadrosauridae

Hadrosauridae is a family of ornithopod dinosaurs commonly known as duck-billed dinosaurs, after the flattened, broadened snouts that give their skulls a duck-bill appearance. Descended from iguanodontian ancestors, they were among the most dominant and diverse large herbivores of the Late Cretaceous, especially in Asia and North America, and near the close of the period several lineages dispersed into Europe, Africa, and South America. Their success is often attributed to their grinding teeth, which were stacked into complex batteries that provided an efficient chewing surface for processing tough vegetation. The family divides into two principal subfamilies: the Lambeosaurinae, distinguished by hollow cranial crests and tubes, and the Saurolophinae, which bore solid crests or none at all. A grade of early-diverging taxa such as Eotrachodon, Aquilarhinus, and Yamatosaurus falls outside both subfamilies. Hadrosaurids were facultative bipeds, with juveniles of some species walking mostly on two legs and adults shifting toward walking on all four.