Hadrosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Ornithopoda > Iguanodontia > Ankylopollexia > Styracosterna > Hadrosauriformes > Hadrosauroidea > Hadrosauridae

Overview: The vast majority of dinosaur fossils described from the United States come from the western part of the country. Exposed rock layers dated to the Mesozoic Era are more common there, unlike in the east, where erosion in some areas has left only pre-Mesozoic rocks exposed and sediment buildup lower down has covered them. Still, a number of dinosaurs have been found and described from the east, including some of the first ever to be named in North America. One of these dinosaurs was Hadrosaurus, described in 1858 by the renowned paleontologist Joseph M. Leidy. The first remains of the animal were found a couple decades earlier in New Jersey, quite on accident by a local man excavating for marlstone. More fossils would later be recovered at this same site, making Hadrosaurus one of the more completely known dinosaurs at the time.

Hadrosaurus would prove a significant discovery. Its limb bones showed it was capable of walking on its hind limbs, which had implications for earlier restorations of dinosaurs like Iguanodon (most famously depicted previously at Crystal Palace Park in London), which had been interpreted as entirely quadrupedal animals. The actual situation with Hadrosaurus was a bit more complex, as it belonged to a lineage that could actually walk in both fashions. Hadrosaurus would go on to become the namesake of both the family Hadrosauridae and the superfamily Hadrosauroidea – the clades containing the famous “duck-billed” dinosaurs. Among the hadrosaurids, Hadrosaurus itself is usually treated as a basal member. It was average-sized, at about eight meters long. Like all of its kin, it possessed both a beak and a large number of teeth lining the back of its jaws.