'bulky lizard') is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation in New Jersey about 83.6 to 77.9 Ma.

Hadrosaurus were ponderously built animals equipped with keratinous beaks for cropping foliage and a specialized and complex dentition for food processing.

The specimen was collected in 1858 from the Woodbury Formation in New Jersey, US, representing the first dinosaur species known from more than isolated teeth to be identified in North America.

[2][3][4][5] In 1838, John Estaugh Hopkins was digging in a marl pit (on a small tributary of the Cooper River in Haddonfield, New Jersey, and part of the Campanian-age Woodbury Formation) when he uncovered large bones.

Leidy's monograph Cretaceous Reptiles of the United States, describing Hadrosaurus more completely, and with illustrations, was written in 1860, but the American Civil War delayed its publication until 1865.

The entire skeleton was completely assembled in 1868 by a team including English sculptor and naturalist Benjamin Waterhouse Hawkins and was put on display at Philadelphia Academy of Natural Sciences.

However, from November 22, 2008, to April 19, 2009, a fully assembled cast of the skeleton, and an exhibit about the science and culture surrounding the dinosaur's discovery, was open to the public.

[6] Despite the fact that the family Hadrosauridae has Hadrosaurus as its type genus, the skeleton lacks a skull and was long viewed as too incomplete to compare to other hadrosaurs for classification purposes, leading most scientists to consider it a nomen dubium, or dubious name.

[10] However, a re-evaluation of the fossil material in 2011 noted several distinct characteristics of the skeleton that could allow the genus Hadrosaurus and species H. foulkii to remain in use as valid taxa.

[10] Jinzhousaurus yangi Fukuisaurus tetoriensis Penelopognathus weishampeli Equijubus normani Probactrosaurus gobiensis Eolambia caroljonesa Protohadros byrdi Tanius sinensis Bactrosaurus johnsoni Glishades ericksoni Gilmoreosaurus mongoliensis Huehuecanauhtlus tiquichensis Jintasaurus meniscus Tethyshadros insularis Hadrosaurus foulkii Acristavus gagslarsoni Maiasaura peeblesorum Brachylophosaurus canadensis Shantungosaurus giganteus Edmontosaurus annectens Edmontosaurus regalis Derived saurolophines → Aralosaurus tuberiferus Jaxartosaurus aralensis Tsintaosaurus spinorhinus Pararhabdodon isonensis Derived lambeosaurines → In 2003, Rothschild and colleagues performed a study looking for epidemiology of tumors in dinosaurs.

Evidence of tumors, including hemangiomas, desmoplastic fibroma, metastatic cancer and osteoblastoma were discovered in specimens of Hadrosaurus by analyzing dinosaur vertebrae using computerized tomography and fluoroscope screening.