Hadrosaurids, maening "heavy lizard," are members of the ornithischian family Hadrosauridae. This group is also known as the duck-billed dinosaurs, for the flat, duck-bill appearance of their mouths. The family, which includes ornithopods such as Edmontosaurus and Parasaurolophus, was a common herbivore in the Upper Cretaceous Period of what is now Asia, Europe, Antarctica, South America and North America.  Hadrosaurids are descendants of the Upper Jurassic/Lower Cretaceous iguanodontian dinosaurs and had a similar body layout. Like the rest of the ornithischians, these animals had a predentary bone and a pubic bone which was positioned backwards in the pelvis. Hadrosaurids are divided into two principal subfamilies: the lambeosaurines (Lambeosaurinae), which had hollow cranial crests or tubes, and the saurolophines, identified as hadrosaurines in most pre-2010 works (Saurolophinae or Hadrosaurinae), which lacked hollow cranial crests (solid crests were present in some forms). Saurolophines tended to be bulkier than lambeosaurines. Lambeosaurines are divided into Aralosaurines, Lambeosaurines, Parasaurolophines and Tsintaosaurines, while Saurolophines include Saurolophus, Brachylophosaurines and Kritosaurines.

Hadrosaurids (specifically Edmontosaurus [called duck-billed dinosaurs in the series]) appear in "Dinosaurs,"''Giants," and "Crocodilian."