Temporal range: Late Cretaceous, 77–75.7Ma
|Mounted skeleton, Royal Ontario Museum|
Corythosaurus // is a genus of 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. 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. 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.
Corythosaurus is known from many complete specimens, including the 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. 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. Like a trombone, the air would travel through many chambers in the crest, and then get amplified when Corythosaurus exhaled. 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.
The two species of Corythosaurus are known from slightly different levels of the Dinosaur Park Formation. Both still existed with theropods and other ornithischians, like Daspletosaurus, Brachylophosaurus, Parasaurolophus, Scolosaurus, and Chasmosaurus.
Discovery and species
The first specimen, AMNH 5240, was discovered in 1912 by Barnum Brown in Red Deer River, Alberta, Canada. 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. The skeleton was articulated, and only missing about the last 0.61 metres (2.0 ft) of the tail and the forelimbs. 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. Impressions of the integument were preserved covering over a large part of the skeletons outlining, and shows the form of the body. 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.
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". The binomial of C. casuarius means "Cassowary-like reptile, with a Corinthian helmet crest". The species name of C. intermedius is derived from its apparent intermediate position according to Parks (1923).
The two best preserved specimens of Corythosaurus, found by Charles H. Sternberg in 1912, were sunk while being carried to the United Kingdom in 1917, during World War One. They were being sent to Arthur Smith Woodward, a paleontologist in England, when the ship transporting them was sunk in the middle of the ocean.
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, although C. intermedius has been recognized as valid in some studies. C. intermedius lived at a different time then C. casuarius, and the species are not identical, which supported the separation of them in a 2009 study.
Benson et al. (2012) estimated that Corythosaurus has an average length of 9 metres (30 ft). An earlier length estimate, authored by Richard Swann Lull and published in 1942, found a slightly longer total length of 9.4 m (31 ft). This is a similar size to Lambeosaurus lambei, another Canadian lambeosaurine. In 1962, Edwin H. Colbert used models of specific dinosaurs, including Corythosaurus, to estimate its weight. The Corythosaurus model was crafted by Vincent Fusco, modelled after a mounted skeleton, and supervised by Barnum Brown. After testing, is was concluded that the average weight of Corythosaurus was 3.82 tonnes (3.76 long tons; 4.21 short tons). More recent size estimates of Corythosaurus, 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).
Over 20 skulls have been found from this dinosaur. As with other lambeosaurs, the animal bore a tall, elaborate bony crest atop its skull, which contained the elongate nasal passages. The nasal 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, so now the width is about two-thirds what it would have been in real life. The compression also caused the nasals to shift were they pressed down on the premaxillaries. Because they were pressed on the premaxillaries, the nasal closed the nares. Apart from the compression, the skull appears to be normal.
The crests of Corythosaurus resemble that of a cassowary, or a Corinthian helmet. They are formed by a combination of the nasals, prefrontals and frontals, like in Saurolophus, but instead of projecting backwards as a spine, it rises up to make the highest point of 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 made up most of the crest, as they extend from the beaks tip to the highest spot along the crest. Unlike in other genera, the nasals meet in the centre and are not separated in front by an ascending premaxillary process. The prefrontals also make up part of the crest, and in the crest they are triangular in shape. The prefrontals do not join with the frontals anywhere near the orbital border. On the top and back of the crest, the whole external face is covered by the frontals. They end at the back of the squamosals in a hooked, short process.
The mouth of the holotype of Corythosaurus is narrow, and the nares are small. Like in Saurolophus, the expanded portion of the premaxillary in front of the narial opening is elongate. This is different from in Kritosaurus, where the bill is short and the nares extend far forward. At the end of the bill, the two nasal unite into one. The holotypes inferior process of the premaxillary is shorter than in Kritosaurus and Saurolophus, and the process does not unite with the lachrymal, also unlike in those genera. The lower jaw is of the holotype 66.9 centimetres (26.3 in) long, and 10 centimetres (3.9 in) deep. The total length of the crest from the beak to the upmost tip is of the type specimen is 83.7 centimetres (33.0 in), its total length is 81.2 centimetres (32.0 in), and height 70.8 centimetres (27.9 in).
In the holotype of C. casuarius, the sides and tail of the body are covered in scales. There are polygonal tuberculate scales, and they vary in size over different sections of the body, and there are 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. Separating the polygonal scales of C. casuarius are shield feature-scales, which are arranged close together in rows. Fossilized tendons are present on all the vertebrae, except for in the cervical region. On no vertebrae do the tendons extend below the transverse processes. Each tendon is flattened at it origin, and ovoid in the central rod, ending at a rounded point.
Excellent extensive skin impressions have been found on Edmontosaurus annectens and Corythosaurus casuarius. Notable integument has also been found on Brachylophosaurus canadensis, Gryposaurus notabilis, Parasaurolophus walkeri, Lambeosaurus magnicristatus, L. lambei, Saurolophus angustirsotris and 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 present 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.
A set of characters was identified by Barnum Brown in 1914. They distinguish Corythosaurus from all other hadrosaurids from Alberta, and are listed below: a comparatively short skull with a high helmet-like crest formed by the nasals, prefrontals and frontals; the nasals not being separated in front by the premaxillaries; a narrow beak, with an expansion in front of an elongated naris; and a small narial opening.
In 1916, Brown expanded the character set to include more features, and the revised version is listed below: a comparatively short skull with a high helmet-like crest formed by nasals, prefrontals and frontals; the nasals not being separated in front by premaxillaries; a narrow beak, expanded section in front of the nares elongated; a small narial opening; a vertebral formula of 15 cervicals, 19 dorsals, 8 sacrals, and 61+ caudals; possession of dorsal spines of a medium height; high anterior caudal spines; long chevrons; long scapulae, possessing a blade of medium width; a radius considerably longer than humerus; comparatively short metacarpals; an anteriorly decurved ilium; a long ischium with a foot-like terminal expansion; a pubis with an anterior blade that is short and broadly expanded at end; a femur that is longer than the tibia; the phalanges of pes are short; that the integument over the sides and tail composed of polygonal tuberculate scales without pattern but graded in size in different parts of the body; and a belly with longitudinal rows of large conical limpet-like scales separated by uniformly large polygonal tubercles.
Originally, Brown referred to Corythosaurus as a member of the family Trachodontidae (now Hadrosauridae), although many paleontologists now classify it in Lambeosaurinae. Inside Trachodontidae were the subfamilies Trachodontinae and Saurolophinae. Brown classified Hadrosaurus, Trachodon, Claosaurus, and Kritosaurus in Trachodontinae, and Corythosaurus, Stephanosaurus, and Saurolophus in Saurolophinae.
Later, Brown revised the phylogeny of Corythosaurus, and found that it was closely related, and possibly ancestral to Hypacrosaurus. The only differences he found between them were the developement of the vertebrae, and the proportions of the limbs. During a study of dinosaurian ilia in the 1920s, Alfred Sherwood Romer proposed that the two orders of dinosaurs might have evolved separately, and that birds, based on the shape and proportions of their ilia might truly be specialized ornithischians. He used both Tyrannosaurus and Corythosaurus as a base model to analyze which theory is more likely true. He found that even though birds are thought of as saurischians, it is very plausible for them to have evolved their specific pelvic musculature and anatomy if they evolved from ornithschians like Corythosaurus. However, even though Corythosaurus does resemble modern birds in pelvic structure more than saurischians, birds are now thought to have descended from the latter.
Corythosaurus is currently classified as a hadrosaurid, in the subfamily Lambeosaurinae. It is related to other hadrosaurs such as Hypacrosaurus, Lambeosaurus and Olorotitan, with the exception of Olorotitan they all share similar looking skulls and crests. However, research published in 2003 has suggested that even though it possesses a unique crest, Olorotitan is Corythosaurus closest known relative. Benson et al. (2012) found that Corythosaurus was closely related to Velafrons, Nipponosaurus, and Hypacrosaurus, and said that they formed a group of fan-crested lambeosaurines.
A cladogram was made by Prieto-Márquez et al. in 2013. It show that Corythosaurus falls inside a clade with Hypacrosaurus, Velafrons, Olorotitan, Magnapaulia, Amurosaurus, Blasisaurus, Sahaliyania, and Arenysaurus. A smaller version of the cladogram is shown below:
Comparisons between the scleral rings of Corythosaurus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals. The sense of hearing in hadrosaurids, specifically such as Lophorhothon, also seems to have been greatly developed because of an elongated lagena. The presence of a thin caliper (an ear bone found in reptiles), combined with a large eardrum implies the existence of a sensitive middle ear. It is possible that hadrosaurid ears are sensitive enough to detect as much sound as a modern crocodilian.
The internal structures of the crest of Corythosaurus are quite complex, making a call that could be used for warning or attracting a mate. Nasal passageways of Corythosaurus, as well as Hypacrosaurus and Lambeosaurus are S-shaped, with Parasaurolophus only possessing U-shaped tubes. Any vocalization would travel through these elaborate chambers, and probably get amplified. Scientists speculate that Corythosaurus could make loud, low pitched cries "[l]ike a wind or brass instrument, such as a trombone". The sounds could serve to alert other Corythosaurus to the presence of food or a potential threat from a predator. The nasal passages emit low-frequency sounds when Corythosaurus exhaled. The individual crests would produce different sounds, so it is likely that each species of lambeosaurine would have had a unique sound among its species. However, even though the range for different lambeosaurine species are not the same, they all probable made low-picthed sounds. This might be because low sounds (below 400 Hz) travel a set distance in any environment, with higher (above 400 Hz) sounds travelling differing distances.
Originally, crested hadrosaurs were thought to be aquatic, based incorrectly on webbing that is now known to be padding. The theory was that the animals could swim deep in the water, and use the crest to store air to breath. However, it has now been proven that the crest did not have any holes in the end, and the water pressure at even 3 metres (9.8 ft) would be too great for the lungs to be able to inflate.
Corythosaurus casuarius is one of a few lambeosaurines, along with Lambeosaurus lambei, Hypacrosaurus stebingeri and H. altispinus, to have had juveniles assigned to it. Juveniles are harder to distinguish, because at a young age they lack the larger crests of adults. As they age, lambeosaurine crest tend to grow and become more prominent come maturity. In the Dinosaur Park Formation, over fifty articulated specimens have been found, coming from many different genera. This creates a problem of juveniles of the taxa being hard to identify as coming from one or another. Earlier, four genera and thirteen species were recognized from the formations area, but that was most likely because paleontologists used to use differences in size and crest shape to differentiate taxa. The smallest specimens were recognized as Tetragonosaurus (a synonym of Procheneosaurus). The largest skeletons were called either Corythosaurus of Lambeosaurus, with the exception of an adult being recognized as Parasaurolophus. Small lambeosaurines from the Horseshoe Canyon Formation were referred to Cheneosaurus.
Corythosaurus started developing its crest when half the size of adults, but Parasaurolophus juveniles grew crests when only 25% as long as adults. Juvenile Corythosaurus, along with adults, had a premaxilla-nasal fontanelle. Young and adult Corythosaurus are similar to Lambeosaurus and Hypacrosaurus but dissimilar to Parasaurolophus in that the sutures of the skull are sinuous, and not smooth and straight. This feature helps differentiate parasaurolophins from lambeosaurins. Generally, the crests of juveniles of lambeosaurines like Corythosaurus, Lambeosaurus, Hypacrosaurus stebingeri, parasaurolophins like Parasaurolophus, and primitive lambeosaurines like Kazaklambia are quite alike, although other features can be used to distinguish them.
Work by Dodson (1975) recognized that there were many less taxa present in Alberta. Tetragonosaurus was found to be juveniles of Corythosaurus or Lambeosaurus. T. erectofrons was assigned to Corythosaurus based largely on biometric information. The only non-typic specimen of Tetragonosaurus, assigned to T. erectofrons, was found later to be referable to Hypacrosaurus, although the holotype of the species was still found to be assignable to Corythosaurus.
Corythosaurus was an ornithopod, and therefore a herbivore. Benson et al. (2012) realized that the beak of Corythosaurus was shallow and delicate, and concluded that it must have been used to feed upon soft vegetation. Based on the climate of the Late Cretaceous, they 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.
Fossils have been found in the upper Oldman Formation and lower Dinosaur Park Formation of Canada. The Oldman Formation dates to the Campanian, about 77.5 to 76.5 million years ago, and the Dinosaur Park Formation dates from 76.6 to 74.8 million years ago. Corythosaurus lived from ~77–75.7 million years ago. In the Dinosaur Park Formation C. casurarius lived from 76.6 to 75.9 mya, with C. intermedius living from 75.8 to 75.7 mya. In the Oldman Formation C. casuarius, the only species of Corythosaurus from the deposits, lived about 77 to 76.5 mya. The holotype specimen was clearly a carcass that had floated up on a beach, as Unio shells, water-worn bones, and a baenid turtle were preserved all around. Corythosaurus probably lived in a woodland forest, and might have occasionally wandered into swampy areas.
A few fauna are known from the upper section of the Oldman Formation, and Corythosaurus casuarius as well as C. intermedius are among the taxa. Also from the section of the formation are the theropods Daspletosaurus, and Saurornitholestes, the hadrosaurids Brachylophosaurus, Gryposaurus and Parasaurolophus, and the ankylosaurid Scolosaurus, and the ceratopsians Coronosaurus and Chasmosaurus. Other genera are known, but do not persist from the upper section of the formation, and therefore are not contemporaries of Corythosaurus.
Corythosaurus casuarius is widespread throughout the lower unit of the Dinosaur Park Formation. 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, and also in the Wind River Basin and the Wheatland County area. Corythosaurus lived alongside numerous other giant herbivores, such as the hadrosaurids Gryposaurus and Parasaurolophus, the ceratopsids Centrosaurus and Chasmosaurus, and ankylosaurids Scolosaurus, Edmontonia and Dyoplosaurus in the earliest stages of the formation, Dyoplosaurus, Panoplosaurus and Euoplocephalus in the middle age, and Euoplocephalus alone in later stages of the formation. Studies of the jaw anatomy and mechanics of these dinosaurs suggests they probably all occupied slightly different ecological niches in order to avoid direct competition for food in such a crowded eco-space. The only large predators known from the same levels of the formation as Corythosaurus are the tyrannosaurids Gorgosaurus libratus and an unnamed species of Daspletosaurus.
Thomas M. Lehman has observed that Corythosaurus hasn't been discovered outside of southern Alberta even though it is one of the most abundant Judithian dinosaurs in the region. Large herbivores like the hadrosaurs living in North America during the Late Cretaceous had "remarkably small geographic ranges" despite their large body size and high mobility. This restricted distribution strongly contrasts with modern mammalian faunas whose large herbivores' ranges "typical[ly] ... span much of a continent."
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