Hadrosaurs

The ornithopod lineage stretches back to the earliest Jurassic with small bipeds like Heterodontosaurus. Over 130 million years it produced a succession of increasingly large and specialized herbivores: the iguanodonts of the Early Cretaceous, then the true hadrosaurs, which became the most abundant large dinosaurs on Earth during the final 15 million years of the Mesozoic.

Hadrosaur success rested on a feeding innovation unlike anything before or since: a dental battery of up to 1,400 teeth arranged in stacked columns, constantly replacing from below like a conveyor belt. This allowed them to process tough, abrasive vegetation that other herbivores couldn't handle. Fossilized gut contents and tooth wear patterns reveal a diet of pine needles, seeds, and fibrous plant material — food sources that were abundant but demanded extreme dental hardware.

The crested hadrosaurs — Parasaurolophus, Corythosaurus, Lambeosaurus — added another dimension: hollow, resonating crests connected to the nasal passages that functioned as low-frequency sound instruments. CT scans have allowed scientists to reconstruct the sounds these animals may have made, suggesting dense herds communicating across forested floodplains in ways more sophisticated than any other dinosaur group.