Hadrosaurus (Greek: sturdy lizard) is a hadrosaurid dinosaur genus. In 1858, a skeleton of a dinosaur from this species was the first full dinosaur skeleton establishes in North America, and in 1868 it became the first ever mounted dinosaur skeleton. Hadrosaurus foulkii is the only species in this class, and as of 1991 is the official state dinosaur of New Jersey - a judgment brought about by a local teacher, Joyce Berry.
In 1838, William Estaugh Hopkins was digging in a marl pit when he exposed large bones. He had the bones on show at his home, Birdwood in Haddonfield, New Jersey. In 1858 these bones sparked the attention of a visitor, William Parker Foulke. The skeleton was dug out from the marl pit in 1858 by Foulke. In the same year, the species was named by paleontologist Joseph Leidy in the same year, from an approximately complete set of limbs, along with a pelvis, several parts of the feet, twenty-eight vertebrae (including eighteen from the tail), eight teeth and two small parts of the jaw. Leidy recognized that these bones were from a dinosaur by their resemblance to those of the Iguanadon, exposed in England some decades before, but the skeleton of Hadrosaurus was far more entire and was at the time the most complete dinosaur skeleton known. Leidy's monograph Cretaceous Reptiles of the United States, telling Hadrosaurus more completely and with illustrations, was written in 1860 but the American Civil War postponed its publication until 1865. Leidy reconstructed Hadrosaurus as a biped, in contrast to the view at the time that such dinosaurs were quadrupedal. The entire skeleton was entirely assembled in 1868 by a team including English sculptor and naturalist Benjamin Waterhouse Hawkins and was put on show at Philadelphia Academy of Natural Sciences, where it remains available for public viewing.Despite the fact that the family Hadrosauridae is named after this genus, there is no skull known. The skeleton is indistinguishable from that of other hadrosaurins.