Temporal range: Late Cretaceous, 76.5–74.8Ma
|Mounted skeleton, Royal Ontario Museum|
Corythosaurus // 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.
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.
- 1 Etymology
- 2 Discovery and species
- 3 Description
- 4 Classification
- 5 Paleobiology
- 6 Paleoecology
- 7 Footnotes
- 8 References
- 9 External links
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. As well as an almost complete skeleton, the find was remarkable because much of the creature's fossilized 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.
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.
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 recent studies.
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 to 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.
Benson et al. (2012) estimated that Corythosaurus has an average length of 9 metres (30 ft).
The exact number of rows of teeth in the holotype is unknown, but there are about 34 rows visible in the maxilla, and 36 in the dentary. Like in Kritosaurus, the anterior end of the dentary is deflected. The maxilla and the dentary are both short. In Trachodon and Stephanosaurus, the dentary is straight, but this could have been caused by crushing. The mouth of Corythosaurus is narrow, and the nares are small. Like in Saurolophus and Trachodon, 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 inferior process of the premaxillary is shorter than in Kritosaurus, Trachodon, and Saurolophus, and the process does not unite with the lachrymal, also unlike in those genera.
The lower jaw is 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 83.7 centimetres (33.0 in). The skull is also 81.2 centimetres (32.0 in) long and 70.8 centimetres (27.9 in) tall.
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 caudals, 19 dorsals, 8 sacrals, and 61+ cervicals; 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 Corythosaurus to the family Trachodontidae, 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.
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, recent research has suggested that Olorotitan is Corythosaurus closest known relative even though it doesn't share as many skull characteristics as other lambeosaurs. 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. The cladogram is 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 also seems to have been developed. 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.
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 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, although they are not as large as in Stephanosaurus. 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.
Theories of crest use
Originally, crested hadrosaurs were thought to be aquatic, based incorrectly on webbing that is now known to be padding. Earlier, the crests were thought to be for breathing, and were suspected of being a snorkel for the animal. 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 to great for the lungs to be able to inflate.
Another snorkel theory involved the crests being used as reserves for air, so it could be breathed while submerged. The problem with this hypothesis was that unless the crests could pressurize the air, the lungs would also not be able to inflate.
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.
In Corythosaurus, 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.
Tendon bones are present on all the vertebrae, except for in the cervical region. On no vertebrae do the tendon bones extend below the transverse processes. Each tendon is flattened at it origin, and ovoid in the central rod, ending at a rounded point.
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. Apart from Corythosaurus very little other skin has been preserved on the feet of hadrosaurids. Saurolophus angustirsotris is the only other hadrosaurid that has a fair amount of leg skin preserved.
Excellent extensive skin impressions have been found on Edmontosaurus annectens and Corythosaurus casuarius. Skin 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 and C. casuarius are similar, and are also similar to S. angustirsotris.
Development and synonyms
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. The age in which individuals developed crests might influence why Parasaurolophus has such a large crest compared with other lambeosaurines. Juvenile Corythosaurus, along with adults, had a premaxilla-nasal fontanelle.
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 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 76.5 to 75.5 million years ago, and the Dinosaur Park Formation dates from 76.6 to 74.8 million years ago, so Corythosaurus lived from ~76.5–74.8 million years ago. 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 is among the genera. 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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