hadrosaurids

Hadrosaurids, or duck-billed dinosaurs, are a diverse group of herbivorous ornithopods within the family Hadrosauridae. They originated in the Early Cretaceous and flourished through the Late Cretaceous, with fossils dating from about 125 to 66 million years ago. They are among the most widespread and morphologically varied ornithopods, with dozens of described genera.

Morphology and dentition: Hadrosaurids are characterized by a broad, flattened rostrum and a keratinous beak for cropping vegetation, and a complex dental system of hundreds of teeth arranged in self-sharpening dental batteries that replaced worn teeth and enabled efficient processing of tough plants. Most species could walk on two legs or four, with hind limbs typically longer than the forelimbs; some individuals were facultative bipeds.

Classification: Two major subgroups are recognized: Hadrosaurinae (the hadrosaurines) and Lambeosaurinae (the crested hadrosaurs). Hadrosaurines typically have solid skulls and relatively small, rounded crests, while lambeosaurines have hollow, elaborately shaped cranial crests that likely served display or acoustic functions. Notable hadrosaurines include Edmontosaurus and Kritosaurus; notable lambeosaurines include Parasaurolophus, Corythosaurus, and Lambeosaurus.

Paleobiology and ecology: Hadrosaurids were among the most common large herbivores in North American and Asian Cretaceous ecosystems. Evidence from bonebeds and trackways indicates social behavior and possibly seasonal migrations. They fed on a variety of vegetation, including ferns, conifers, and flowering plants.

Fossil record and distribution: Their remains have been found across a wide geographic range, reflecting their success in Late Cretaceous habitats.