Hadrosauroidea

Hadrosauroidea is a superfamily of ornithischian dinosaurs, commonly referred to as duck-billed dinosaurs and their close relatives. This clade encompasses the diverse family Hadrosauridae as well as more basal ancestors that predate the characteristic features of the derived duck-bills. The name is derived from the Greek words for "bulky" or "stout" and "lizard," a reference to the generally robust body plan of these animals.

These herbivores appeared during the Early Cretaceous and rose to prominence during the Late Cretaceous period. Their fossils have been discovered across the globe, including sites in North America, Asia, Europe, South America, and Antarctica. Members of this group are characterized by broad, toothless beaks used for cropping vegetation. While primitive hadrosauroids lacked the sophisticated dental batteries of their later cousins, many still exhibited teeth suited for processing tough plant matter.

Hadrosauroids were typically facultative bipeds, meaning they could walk on two legs for speed but likely adopted a quadrupedal posture while resting or feeding to support their weight. The evolutionary success of this group is evidenced by their high diversity and wide geographic distribution shortly before the Cretaceous-Paleogene extinction event. They represent a critical lineage in understanding the adaptation of herbivorous dinosaurs to various terrestrial ecosystems.