Corythosaurus

Corythosaurus /ˌkɒrɨθɵˈsɔrəs/ is a genus of duck-billed dinosaur from the Upper Cretaceous Period, about 76.5-74.8 million years ago. It lived in what is now North America. Its name means "helmet lizard", derived from Greek. It was named and described in 1914 by Barnum Brown, and classified as a trachodontid. Corythosaurus 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. It is known from many complete specimens, including a nearly complete holotype found by Brown in 1912. 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. The specimen was found among marine sediments, and around it were preserved elements of the bivalve Unio, and an indeterminate turtle. The preserved sections of the forelimbs include the scapulae, coracoids, humeri, ulnae, radii, and phalanges.

In 1917, two greatly-preserved specimens of Corythosaurus were being shipped to Arthur Smith Woodward in England. They were sent to the bottom of the ocean when their carrier was sunk.

Many species of Corythosaurus were known before 1975, but in that year, Peter Dodson studied and described many gender-related crest traits. These traits showed that the many species which were distinguished by crest shape and size were likely synonyms. Dodson found that all the species were the same, but now C. intermedius is recognized as valid. Corythosaurus is now thought to be a lambeosaurine, related to Nipponosaurus, Velafrons, Hypacrosaurus, and Olorotitan.

Corythosaurus is known from many skulls with tall crests. The crests resemble the crests of the cassowary and a Corinthian helmet. Originally, the crests were thought to be used as a snorkel, to breathe through when swimming. The problem with that was that there were no holes in the top of the crest to allow air through. Later, they were thought to be air reserves, to breathe when underwater. A problem with that theory was that underwater, unless the animal had some way of pressurizing the air, the lungs would not be able to expand. Currently, the most likely scenario is that the crest was used for vocalization. Like a trombone, the air would travel through many chambers in the crest, and then get amplified when Corythosaurus exhaled. It was thought to be aquatic, based on the misidentification of foot padding, that was thought to be webbing.

Corythosaurus is known from juveniles and adults. Therefore, it is known when it started developing its crests. Its crests started developing when half the size of adults, but Parasaurolophus juveniles grew crests when only 25% as long as adults. The age in which individuals developed crests might influence why Parasaurolophus has such a large crest compared with other lambeosaurines.

Corythosaurus has been preserved with skin impressions. The impressions are of polygonal tuberculate scales, and they vary in size over different sections of the body. Other impressions are of conical limpet-like scales that are only preserved on a fold of skin on the back of the tibia. The skin preserved on the tibia was probably from the bottom of the belly, instead of on the leg, so leg scalation is not well known among hadrosaurids. Separating the polygonal scales of C. casuarius are shield feature-scales, which are arranged close together in rows.

Based on the climate of the Late Cretaceous, Benson et al. (2010) guessed that Corythosaurus would have been a selective feeder, eating only the juiciest fruits and youngest leaves. Corythosaurus specimens have been preserved with its last meal in its chest cavity. Inside the cavity were remains of conifer needles, seeds, twigs, and fruits, meaning that Corythosaurus probably fed on all of these.

Corythosaurus is well-known from two formations of Alberta, the Oldman and Dinosaur Park formations. In the Dinosaur Park Formation, along with the Judith River, and Mesaverde formations, and also the Wind River Basin and the Wheatland County areas, Corythosaurus was found associated with Centrosaurus. Many taxa were found alongside Corythosaurus is the formations, and the only two large predators found in the same area as Corythosaurus were Gorgosaurus and Daspletosaurus.

etymology
Corythosaurus was named after a specimen collected by Barnum Brown in 1912. It is among many lambeosaurines that possess crests, and it was the crest that lends Corythosaurus its name. Corythosaurus is derived from Greek, and means "helmeted lizard".

Discovery and species
The first specimen, AMNH 5240, was discovered in 1912 by Barnum Brown in Red Deer River, Alberta, Canada.[2] As well as an almost complete skeleton, the find was remarkable because much of the creature's fossilized skin had also survived.[3] The specimen came from the Belly River Group of the province.[2] The left or underside of the skeleton was preserved in carbonaceous clay, making it difficult to expose the skin.[3] The skeleton was articulated, and only missing about the last 0.61 metres (2.0 ft) of the tail and the forelimbs.[3] Both scapulae and coracoids are preserved in position, but the rest of the forelimbs are gone, except for phalanges and pieces of humeri, ulnae and radii. Apparently the remaining forelimbs were weathered or eroded away.[3] Impressions of the integument were preserved covering over a large part of the skeletons outlining, and shows the form of the body.[3] Another specimen was found in 1914 by Brown and Peter Kaisen. Both specimens are now housed in the American Museum of Natural History in their original death poses.[4]

The two best specimens of Corythosaurus, found by Charles H. Sternberg in 1912, were sunk while being carried to the United Kingdom in 1917. They were being sent to Arthur Smith Woodward, a paleontologist in England, when they were sunk in the middle of the ocean.[5]

There were originally up to seven species described including C. casaurius, C. bicristatus, C. brevicristatus, C. excavatus, C. frontalis, and C. intermedius. In 1975 Peter Dodson studied the differences between the skulls and crests of different species of lambeosaurine dinosaurs. He found that the differences in size and shape may have actually been related to the gender and age of the animal. Now only one species is recognized for certain, C. casuarius,[6] although C. intermedius has been recognized as valid in some recent studies.