hadrosaurians

Hadrosaurians are a diverse group of herbivorous, beaked dinosaurs within the clade Ornithopoda, commonly referred to as duck-billed dinosaurs. The group includes the true hadrosaurs (Hadrosauridae) and their close relatives, and they are among the most widespread and varied herbivores of the Late Cretaceous. They inhabited a range of environments and ranged in size from small to very large.

Anatomy and feeding: Hadrosaurians possessed a broad, keratinous beak at the front of the mouth and rows of densely packed teeth in dental batteries that could be worn down and replaced as needed. This arrangement allowed continuous processing of tough vegetation. The skull often carried a crest in some lineages; lambeosaurines have elaborate hollow crests, while hadrosaurines generally lack such crests or have simpler structures. Crest shape is diagnostic for groups and likely served in display and possibly vocal communication.

Temporal and ecological range: They first appear in the Early Cretaceous and become highly successful in the Late Cretaceous, expanding across much of the northern continents and into parts of Asia. They are typically interpreted as herd-forming animals and show evidence of rapid dental replacement and diverse feeding strategies.

Taxonomy and examples: The Hadrosauridae is divided into subfamilies Hadrosaurinae and Lambeosaurinae, including genera such as Edmontosaurus, Kritosaurus, Parasaurolophus, Lambeosaurus, and Corythosaurus. Fossils are especially common in North American deposits, with significant finds in Asia and Europe.

Extinction: Hadrosaurians disappeared at the end of the Cretaceous period, around 66 million years ago, along with most other non-avian dinosaurs.