Hadrosauridae

Hadrosauridae, commonly known as hadrosaurs or duck-billed dinosaurs, is a family of ornithopod dinosaurs that flourished during the Cretaceous period. They are characterized by broad, flattened snouts and a specialized dental apparatus formed from dental batteries that allowed efficient grinding of plant material. The family is traditionally divided into two main subfamilies: Hadrosaurinae, which generally have solid crests or no crests, and Lambeosaurinae, which possess hollow, elaborately shaped cranial crests used in display and possibly vocalization.

The fossil record shows a wide range of sizes and forms, from medium-sized to large herbivores, with adults typically ranging from about 4 to 12 meters in length. Hadrosaurs were primarily herbivorous and capable of both bipedal and quadrupedal locomotion; they could move on two legs for speed or on all fours when feeding or resting. Their environmental distribution was broad, with fossils found across North America, Europe, and Asia, indicating a successful and widespread adaptive radiation in the Late Cretaceous.

Ecology and behavior evidence comes from teeth, skulls, and nesting sites. The dental batteries allowed processing of a variety of vegetation, including tough, fibrous material. In several genera, especially Maiasaura, fossil sites show nesting behavior and possible parental care. Hadrosaurs declined toward the end of the Cretaceous and became extinct at the end-Cretaceous mass extinction.

Notable genera include Edmontosaurus (hadrosaurine), Parasaurolophus, Corythosaurus, Lambeosaurus, Kritosaurus, Hypacrosaurus, and Maiasaura. The group is a key component of North American Cretaceous ecosystems and a focus of study for ornithopod evolution and paleobiology.