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
thumb|left|Fossil holotype specimen AMNH 5240 partially covered in skin impressions
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.
thumb|left|Quarry with one of the specimens lost at sea in 1916
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.
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, 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.
Description
Size
thumb|left|Size of C. casuarius (left, red) and C. intermedius (right, yellow) compared to a human.
Benson et al. (2012) estimated that Corythosaurus has an average length of . 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.
thumb|Skull of [[Royal Tyrrell Museum of Palaeontology|TMP 1984.121.0001]]
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. 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. However, even though the pelvic structure of Corythosaurus and other ornithischians does bear a greater superficial resemblance to birds than the saurischian pelvis does, birds are now known to be highly derived maniraptoran theropods.
thumb|ROM 845, mounted [[skeleton of Corythosaurus cf. intermedius cf. excavatus Parks 1935 at the Royal Ontario Museum]]
Paleobiology
Comparisons between the scleral rings of Corythosaurus and modern reptiles suggest that it may have been cathemeral, meaning it was most active throughout the day at short intervals. The presence of a thin stapes (an ear bone that is rod-like in reptiles), combined with a large eardrum, implies the existence of a sensitive middle ear.
Growth
thumb|left|ROM 759, a juvenile skull, originally named as a separate species, Tetragonosaurus erectofrons
Corythosaurus casuarius is one of a few lambeosaurines, along with Lambeosaurus lambei, Hypacrosaurus stebingeri, and H. altispinus, to have had surviving fossilized juveniles assigned to it. Juveniles are harder to assign to species because, at a young age, they lack the distinctive larger crests of adults. As they age, lambeosaurine crests tend to grow and become more prominent come maturity. In the Dinosaur Park Formation, over fifty articulated specimens have been found that come from many different genera. Among them, juveniles are hard to identify at the species level. Earlier, four genera and thirteen species were recognized from the formation's area when paleontologists used differences in size and crest shape to differentiate taxa. The smallest specimens were identified as Tetragonosaurus, now seen as a synonym of Procheneosaurus, and the largest skeletons were called either Corythosaurus or Lambeosaurus. An adult was even identified as Parasaurolophus.
Work by Dodson (1975) recognized that there were many less taxa present in Alberta. The Oldman Formation dates to the Campanian, about 77.5 to 76.5 million years ago, In it, Corythosaurus was found to be closely associated with the ceratopsid Centrosaurus apertus. Their associating was found in the Dinosaur Park, Judith River, and Mesaverde formations, as well as the Wind River Basin and the Wheatland County area.
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