Corythosaurus (; ) is a genus of hadrosaurid "duck-billed" dinosaur from the Late Cretaceous period, about 77–75.7 million years ago, in what is now western North America. Its name is derived from the Greek word κόρυς, meaning "helmet", named and described in 1914 by Barnum Brown. Corythosaurus is now thought to be a lambeosaurine, thus related to Lambeosaurus, Nipponosaurus, Velafrons, Hypacrosaurus, and Olorotitan. Corythosaurus has an estimated length of and has a skull, including the crest, that is 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 front legs, but was preserved with impressions of polygonal scales. Corythosaurus is known from many skulls with tall crests that resemble those 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. One Corythosaurus specimen has even been preserved with its last meal in its chest cavity. Inside the cavity were remains of conifer needles, seeds, twigs, and fruits, suggesting that Corythosaurus probably fed on all of these.
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.
Discovery and species
The first specimen, AMNH 5240, was discovered in 1911 by Barnum Brown in Red Deer River of Alberta and secured by him in the Fall of 1912.Lowell Dingus and Mark Norell, 2011 Barnum Brown: The Man Who Discovered Tyrannosaurus rex, University of California Press, p. 143 As well as an almost complete skeleton, the find was notable because impressions of much of the creature's skin had also survived. The specimen came from the Belly River Group of the province. The left or underside of the skeleton was preserved in carbonaceous clay, making it difficult to expose the skin to the elements. The skeleton was articulated and missing only about the last of the tail and front legs. Both scapulae and coracoids are preserved in position, but the rest of the front legs are gone (except for phalanges and pieces of the humeri, ulnae, and radii). Apparently, the remaining front legs were weathered or eroded away. Impressions of the integument were preserved covering over a large part of the skeleton's outlining and shows the form of the body. Another specimen, AMNH 5338, 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.
The type species, Corythosaurus casuarius, was named by Barnum Brown in 1914, based on the first specimen collected by him in 1912. AMNH 5240 is thus the holotype. In 1916, the original author, Brown, published a more detailed description that was also based on AMNH 5338, which is therefore the plesiotype. Corythosaurus is among many lambeosaurines that possess crests and it was the crest that lends Corythosaurus its name. The generic name Corythosaurus is derived from the Greek κόρυθος,(korythos), "Corinthian helmet", and means "helmeted lizard". The specific name, casuarius, refers to the cassowary, a bird with a similar skull crest. The full binomial of Corythosaurus casuarius thus means "Cassowary-like reptile, with a Corinthian helmet crest".
The two best preserved specimens of Corythosaurus, found by Charles H. Sternberg in 1912, were lost on December 6, 1916, while being carried by the SS Mount Temple to the United Kingdom during World War I. They were being sent to Arthur Smith Woodward, a paleontologist of the British Museum of Natural History in England, when the ship transporting them was sunk by the German merchant raider in the middle of the ocean.p. 495 in Tanke, D.H. & Carpenter, K. (2001).
There were formerly up to seven species described, including C. casuarius, C. bicristatus (Parks 1935), C. brevicristatus (Parks 1935), C. excavatus (Gilmore 1923), C. frontalis (Parks 1935), and C. intermedius (Parks 1923). 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 sex and age of the animal. Only one species is currently recognized for certain, C. casuarius, although C. intermedius has been recognized as valid in some studies. It is based on specimen ROM 776, a skull found by Levi Sternberg in 1920, was named by William Parks in 1923. Originally, he named it Stephanosaurus intermedius earlier that year. The specific name of C. intermedius is derived from its apparent intermediate position according to Parks. C. intermedius lived at a slightly later time in the Campanian than C. casuarius and the two species are not identical, which supported the separation of them in a 2009 study. The invalid species, C. excavatus (specimen UALVP 13), was based on only a skull found in 1920 and wouldn't be reunited with the rest of its remains until 2012.
Description Size
Benson et al. (2012) estimated that Corythosaurus has an average length of . In 1962, Edwin H. Colbert used models of specific dinosaurs, including Corythosaurus, to estimate their weight. The Corythosaurus model used was modelled by Vincent Fusco, after a mounted skeleton, and supervised by Barnum Brown. After testing, it was concluded that the average weight of Corythosaurus was . The total length of Corythosaurus specimen AMNH 5240 was found to be long, with a weight close to . In 2016, Gregory S. Paul estimated that C. casuarius reached long and in weight and that C. intermedius reached in length and in weight. A "morphologically adult-sized specimen" of C. casuarius measured approximately long.
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.
Skull
Over twenty skulls have been found from this dinosaur. As with other lambeosaurines, the animal bore a tall, elaborate, bony crest atop its skull that contained the elongate narial passages. The narial passages extended into the crest, first into separate pockets in the sides, then into a single central chamber, and onward into the respiratory system. The skull of the type specimen has no dermal impressions on it. During preservation, it was compressed laterally and the width is now about two-thirds of what it would have been in real life. According to Brown, the compression also caused the nasals to shift where they pressed down on the premaxillaries. Because they were pressed on the premaxillaries, the nasals would have closed the nares. Apart from the compression, the skull appears to be normal. Contrary to what Brown assumed, the areas concerned were fully part of the praemaxillae.
As aforementioned, the crests of Corythosaurus resemble that of a cassowary or a Corinthian helmet. They are formed by a combination of the praemaxillae, nasals, prefrontals, and frontals, as in Saurolophus, but instead of projecting backwards as a spine, they rise up to make the highest point above the orbit. The two halves of the crest are separated by a median suture. In front of the orbit, the crest is made of thick bone.
The nasals make up most of the crest. Brown assumed that they extended from the beaks' tip to the highest spot along the crest and that, unlike those in other genera, the nasals meet in the center and are not separated in front by an ascending premaxillary process. However, Brown mistook the praemaxillae for the nasals. The snout is actually largely formed by them and they do separate the nasals. Brown also thought that, on the top and back of the crest, the whole external face is covered by the frontals. Again he made a mistake, as what he assumed to be the frontals are in fact the nasals. The nasals end at the back of the squamosals in a hooked, short process. The prefrontals also make up part of the crest. However, Brown mistook the lower upper branch of the praemaxilla for the prefrontal. The actual prefrontal, which is triangular in shape, is located at the side of the crest base. It was seen by Brown as a part of the frontal. The real frontals, which are largely internal to the crest base structure, are not visible from the side.Weishampel, D.B., Dodson, P., Osmólska, H., & Hilton, Richard P., 2004, The Dinosauria. University of California Press. p. 450
The mouth of the holotype of Corythosaurus is narrow. The praemaxillae each form two long folds that enclose air passages extending the narial passages to the front of the snout. There, they end in narrow openings, sometimes called "pseudonares", which are false bony nostrils. These were mistaken by Brown for the real nares or nostrils. These are actually situated inside the crest, above the eye sockets. As in Saurolophus, the expanded portion of the premaxillary in front of the pseudonaris' opening is elongate. By comparison, the bill of Kritosaurus is short and the pseudonares extend far forward. At the end of the Corythosaurus bill, the two pseudonares unite into one. Because of his incorrect identification, Brown assumed that the holotype's inferior process of the premaxillary was shorter than in Kritosaurus and Saurolophus and that the process does not unite with the lacrimal, which is another difference from those genera. The praemaxilla actually does touch the lacrimal and extends to the rear until well behind the eye socket.
The lower jaw of the holotype is long and deep. The total length of the crest from the beak to the uppermost tip of the type specimen is , its total length is , and its height is .
Soft tissue
In the holotype of C. casuarius, the sides and tail are covered in scales of several types. Polygonal tuberculate scales, covered in small bumps, vary in size across the body. Conical limpet-like scales are preserved only on a fold of skin preserved on the back of the tibia, but this was probably from the bottom of the belly instead of the leg. Separating the polygonal scales of C. casuarius are shieldlike scales, arranged close together in rows. Ossified tendons are present on all the vertebrae, except for those in the cervical region. On no vertebrae do the tendons extend below the transverse processes. Each tendon is flattened at its origin, transversely ovoid in the central rod, and ends at a rounded point.
Aside from those found on Corythosaurus casuarius, extensive skin impressions have been found on Edmontosaurus annectens and notable integument has also been found on Brachylophosaurus canadensis, Gryposaurus notabilis, Parasaurolophus walkeri, Lambeosaurus magnicristatus, L. lambei, Saurolophus angustirsotris, and on unidentified ornithopods. Of these, L. lambei, C. casuarius, G. notabilis, P. walkeri, and S. angustirsotris have preserved polygonal scales. The scales on L. lambei, S. angustirostris, and C. casuarius are all similar. Corythosaurus is one of very few hadrosaurids which have preserved skin impressions on the hind limbs and feet. A study in 2013 showed that, amongst hadrosaurids, Saurolophus angustirostris preserved the best and most complete foot and limb integument, although other species like S. osborni, Edmontosaurus annectens, and Lambeosaurus lambei (= L. clavinitialis) share a fair amount of preserved tissue on those regions.
It was once thought that this dinosaur lived mostly in the water, due to the appearance of webbed hands and feet. However, it was later discovered that the so-called "webs" were in fact deflated padding, much like that found on many modern mammals.
Distinguishing characteristics