Hadrosaurids (Greek: ἁδρός, hadrós, “stout, thick”), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is also known as the duck-billed dinosaurs, for the flat, duck-bill appearance of the bones in their snouts. 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.
Hadrosaurs had a stiff tail that was probably used for balance. They had hoof-like nails on their feet, and bumpy skin. They ran on two legs, holding their tail and head in a horizontal position. They may have walked on all four legs while grazing. Hadrosaurs probably lived near bodies of water, migrating to high ground to lay eggs. It used to be thought that they had webbed hands, but this was an artifact of the fossilization process.
The two major divisions of hadrosaurids are differentiated by their cranial ornamentation. While members of the Lambeosaurinae subfamily have hollow crests that differ depending on species, members of the Saurolophinae (Hadrosaurinae) subfamily have solid crests or none at all. Lambeosaurine crests had air chambers that may have produced a distinct sound and meant that their crests could have been used for both an audio and visual display.
Hadrosaurs are closely related to the Iguanodontids, and are probably their descendants. Hadrosaurs were Ornithischians (the order of bird-hipped dinosaurs) and Ornithopods (“bird-footed” herbivores with hoof-like feet). Hadrosaurs are divided into two groups, the Hadrodsaurinae (non-crested hadrosaurs) and the Lambeosaurinae (hadrosaurs that had skull crests that connected with their nasal passages).
Hadrosaurs lived during the late Cretaceous period. Their fossils have been found in North America, Europe, and Asia.
Although it has been long believed that hadrosaurs originated in Asia, the new find, Protohadros byrdi, seems to shift the birthplace of hadrosaurs to North America. Protohadros byrdi dates from 95.5 million years ago, was recently found in Texas, USA.
The following taxonomy includes dinosaurs currently referred to the Hadrosauridae and its subfamilies. Hadrosaurids that were accepted as valid, but not placed in a cladogram at the time of Prieto-Márquez’s 2010 study, are included at the highest level to which they were placed (either then, or in their description if they postdate the papers used here).
- Family Hadrosauridae
- Subfamily Hadrosaurinae
- Subfamily Saurolophinae
- Subfamily Lambeosaurinae
- Dubious hadrosaurids