Corythosaurus is a genus of hadrosaurid “duck-billed” dinosaur from the Upper Cretaceous Period, about 77–75.7 million years ago. It lived in what is now North America. Its name means “helmet lizard”, derived from Greek κόρυς. It was named and described in 1914 by Barnum Brown. Corythosaurus is now thought to be a lambeosaurine, related to Nipponosaurus, Velafrons, Hypacrosaurus, and Olorotitan. It has an estimated length of 9 metres (30 ft), and has a skull, including the crest, that is 70.8 centimetres (27.9 in) tall.
Corythosaurus is known from many complete specimens, including the nearly complete holotype found by Brown in 1911. The holotype skeleton is only missing the last section of the tail, and part of the forelimbs, but was preserved with impressions of polygonal scales. Corythosaurus is known from many skulls with tall crests. The crests resemble the crests of the cassowary and a Corinthian helmet. The most likely function of the crest is thought to be vocalization. As in a trombone, sound waves would travel through many chambers in the crest, and then get amplified when Corythosaurus exhaled. A Corythosaurus specimen has been preserved with its last meal in its chest cavity. Inside the cavity were remains of conifer needles, seeds, twigs, and fruits: Probably fed on all of these.
Benson et al. (2012) estimated that Corythosaurus has an average length of 9 metres (30 ft). Richard Swann Lull’s earlier length estimate, published in 1942, found a slightly longer total length of 9.4 m (31 ft), a size similar to Lambeosaurus lambei, another Canadian lambeosaurine. In 1962, Edwin H. Colbert used models of specific dinosaurs, including Corythosaurus, to estimate their weight. The Corythosaurus model used, was modeled by Vincent Fusco after a mounted skeleton, and supervised by Barnum Brown. After testing, it was concluded that the average weight was 3.82 tonnes (3.76 long tons; 4.21 short tons). More recent size estimates was published in 2001, find the genus to be among the largest hadrosaurids, only smaller than Shantungosaurus and Parasaurolophus. The total length of Corythosaurus specimen AMNH 5240 was found to be 8.1 m (27 ft), with a weight of 3.0785 tonnes (3.0299 long tons; 3.3935 short tons).
Proportionally, the skull is much shorter and smaller than that of Edmontosaurus (formerly Trachodon), Kritosaurus, or Saurolophus, but when including its crest, its superficial area is almost as large.
The two species of Corythosaurus are both present in slightly different levels of the Dinosaur Park Formation. Both still co-existed with theropods and other ornithischians, like Daspletosaurus, Brachylophosaurus, Parasaurolophus, Scolosaurus, and Chasmosaurus.