Hadrosaurids (meaning “bulky lizards”) were the family of duck-billed, herbivorous dinosaurs. They were the most common dinosaurs. Hadrosaurs ranged in size from 10 to 40 feet (3 to 12 m) long. They had horny, toothless beaks and hundreds of cheek teeth in the sides of their jaws. The duck-billed dinosaurs had the most teeth; they had up to about 960 cheek teeth.

North American Hadrosaurs
by PaleoGuy

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.

Edmontosaurus skull, Oxford University Museum of Natural History

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).

Skull comparison among several hadrosaurids (not to scale)

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.

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