Corythosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Hadrosauridae

Genus:Corythosaurus

Species:Corythosaurus casuarius

Corythosaurus casuarius is one of the best known examples of the hadrosaurs, a family of herbivorous dinosaurs that dominated the Late Cretaceous period (99–66 million years ago). Though Corythosaurus hails from North America, hadrosaurs spanned the globe in great numbers and have yielded some of the most numerous fossil finds from the Late Cretaceous. Corythosaurus alone has offered many fossils, including numerous skulls and a complete skeleton.

What makes Corythosaurus unique, aside from its hollow, helmet-like head crest, is its fossil history. Scientists unearthed the Corythosaurus fossils from the same Canadian site, but they initially thought that they had discovered seven new species, some of them in an entirely different genus. It was not until later that they reconciled the specimens into one genus and species—Corythosaurus casuarius. (One other species, Corythosaurus intermedius, was also eventually recognized.) Well-preserved Corythosaurus fossils have provided valuable insight into dinosaur skin composition and diet.

Classification

Paleontologists traditionally used the hierarchical Linnaean classification system, developed by Carolus Linnaeus in 1735, for dinosaur taxonomy. This system comprises different tiers of classification (such as class, order, family, genus, and species) based on shared characteristics within each grouping. Species, the lowest tier, is based on the most specific shared traits.

According to Linnaean taxonomy, Corythosaurus has been classified under the order Ornithischia. One of two basic orders of dinosaurs, the ornithischians ("bird-hipped") were known for their bird-like hip structure, with their pelvic bones pointed down and back towards the tail. Dinosaurs in this order also tended to be herbivores and to have hoof-like claws on their feet and beak-shaped mouths. (In the twenty-first century some scientists began to challenge the longstanding division of dinosaurs into the orders Ornithischia and Saurischia, but it remained widely accepted.)

The Ornithischia order is broken down even further according to more specific physical characteristics. Corythosaurus is placed in the Hadrosauridae family because of its flat, duck-billed skull, toothless beak, and abundant teeth set back in the cheek, as well as its notable cranial crest. Corythosaurus is also distinct for the hollow plate-like crest that gave the animal its name and further classifies the dinosaur into the Lambeosaurinae subfamily. Corythosaurus casuarius is the type species of the genus.

Scientists may also use another classification system, called phylogenetic or cladistic classification. Cladistics seeks to create groups of organisms based on evolutionary relationships; these groups are called "clades." Cladistic analysis focuses on important key traits and attempts to trace the inheritance of a trait among descendants of a common ancestor.

Within cladistics, hadrosaurids comprise their own clade, or branch, on the dinosaur family tree. This means that all hadrosaurs, including Corythosaurus, share a common ancestor within the larger family of ornithopods. The Hadrosauridae clade branches into smaller, more specific subfamilies, of which Corythosaurus is generally considered to belong to the Lambeosaurinae. As such, Corythosaurus is similar in likeness to another lambeosaurine, Hypacrosaurus, another hollow-crested, duckbilled dinosaur from Late Cretaceous North America, and these lambeosaurines have been grouped together by some researchers into the clade Corythosaurini.

Anatomy

Corythosaurus displayed many of the anatomical features common to its Hadrosauridae family. One of the larger hadrosaurs, Corythosaurus had the typically large torso, long, pointed tail, and curved neck with shorter forelimbs than hind. It also possessed three-toed, hoof-clawed feet and two hands shaped like mittens. The skeletal structure of its arms and legs indicate that Corythosaurus was both bipedal and quadrupedal. It likely spent much of its time on four limbs but rose into a bipedal stance for faster travel.

Corythosaurus possessed the characteristic duckbilled head of the hadrosaurs. It had a long head that tapered to a narrow snout capped in a beak-like, toothless mouth. Its small plant-eating teeth were housed in rows within its cheek, to the side and further back. As with other members of its family, Corythosaurus possessed hundreds of these teeth. The wide, flat crest atop its head is notable for its helmet-like shape, from which Corythosaurus took its name. The crest itself is hollow, and the nasal passages extended up through the crest. This physiology made the crest more than a visual ornament—many researchers believe Corythosaurus could use the crest to emit horn-like intonations that might have been used for signaling and other forms of communication within its herd.

Dinosaurs have generally been regarded as cold-blooded animals, similar to modern lizards, though the term is deceptive. Modern lizards are ectothermic, meaning that they rely on the sun and other environmental factors to warm their bodies. Though science has traditionally held dinosaurs, specifically non-avian dinosaurs, to be ectothermic, evidence suggests that some might have been endothermic, meaning that they could heat their bodies from within by consuming food. Scientists continue to debate whether hadrosaurs such as Corythosaurus might have been ectotherms or endotherms, or something in between.

Intelligence

Scientists have used encephalization quotient (EQ), based on brain and body size, to estimate animal intelligence. Slower-moving herbivores tend to fall lower on the EQ scale than their faster, carnivorous, predatory counterparts. However, the hadrosaurs as a group appear to have had larger brain-to-body mass ratios and keener senses, placing them higher on the intelligence scale than most other herbivores. They likely ranked between 0.8 and 1.5.

Reproduction and Population

Specific demographic information for Corythosaurus is derived from numerous skulls and skeletons found in the same rock formation in Canada. The abundance of fossil evidence for the Hadrosauridae family indicates that the family and its distinct species likely flourished. Large fossil fields found in North America and Asia show that hadrosaurs traveled in herds that numbered in the hundreds, and scientists suspect that Corythosaurus was also a migratory herd animal.

Existing evidence suggests that most dinosaurs, including hadrosaurs, were oviparous. This means that they reproduced by laying eggs. In fact, the fossil remains of hadrosaurs have contributed a great deal to the study of dinosaur reproduction and nesting. Hadrosaur nesting sites have yielded important egg finds, demonstrating not only the oviparous nature of some (if not all) dinosaurs, but also the nesting tendencies of certain genera. Group nesting sites suggest that herds laid and watched over eggs together, and shell and skeletal evidence reveals that hatchlings likely remained in the nest for a period of time and were fed by their parents or other adult hadrosaurs. Some geographic evidence suggests that hadrosaurs traveled to specific nesting sites to lay and tend their eggs, and that these sites were used by cycling groups of parents that returned to the same ground each year.

Diet

Like other hadrosaurs, Corythosaurus was a plant-eater. Its numerous but small teeth, set well back in its lateral cheeks rather than in the forefront of its mouth, were designed for chewing a variety of foliage, including leaves, seeds, pods, pine needles, and fruits. Its beak-tipped mouth would have served well for tearing and gripping such food. Living in the Late Cretaceous, Corythosaurus would have found an abundance of vegetation to consume. Its diet most likely comprised of such gymnosperms as ferns, conifers, and cycads, and perhaps the newly evolved flowering angiosperms. The skeletal structure and semi-quadrupedal stance indicate that this dinosaur likely grazed on ground foliage and other low-lying vegetation within its reach. Like most herbivores, Corythosaurus probably spent a great deal of time looking for and consuming food.

Behavior

An abundance of fossil evidence found for Corythosaurus and its other relations among the hadrosaurs suggests that these dinosaurs were highly socialized herd animals. More than twenty fossils were found for Corythosaurus at the same fossil site, and many other hadrosaur finds have included the remains of multiple specimens. These fossils, as well as their widespread geographic locations, indicate that hadrosaurs traveled in large groups and migrated across the continents. Some hadrosaurs are even believed to have traveled in groups numbering in the hundreds, and earlier ancestors of Corythosaurus have been called the "sheep" of the Mesozoic.

Most migratory dinosaurs, such as hadrosaurs, likely moved from place to place in search of food and may have traveled with other plant-eating, herding species. Though all fossil evidence is subject to interpretation, it seems likely that Corythosaurus was a fairly gregarious species.

Habitat and Other Life Forms

Thus far, all fossil evidence for Corythosaurus comes from western Canada, indicating that the species thrived in this region during the Late Cretaceous period. However, its fellow hadrosaurs are known to have lived across the globe in great numbers. In Canada and elsewhere, the Late Cretaceous was a time of great change, including plant and animal diversification. The climate differed markedly from that of the same region today. The climate was far warmer, likely sub-tropical, and the land was more likely covered in thick forests and swamps.

By this time, the vast supercontinent of Pangaea had split into two smaller supercontinents, Gondwana and Laurasia. Throughout the Late Cretaceous, tectonic change continued, with the breaking apart of Laurasia into smaller continents. These tectonic shifts brought great changes to the climate and the landscape. Species became more isolated even as new plants and animals emerged. The Late Cretaceous would prove to be the final period of dinosaur life on earth, and dinosaurs shared the land with a diverse variety of insects, birds, mammals, amphibians, and flora.

Evidence suggests that Corythosaurus and its relations benefited from the sudden flourishing of flowering plants across the globe. Their success at foraging on angiosperms and other plant life may have contributed to the decline in some other herbivore species.

The hadrosaurs of western North America shared their landscape with many other great and familiar dinosaurs of the time—including their fellow herbivores, the ceratopsians, and their fierce predators, the tyrannosaurs.

Research

The first Corythosaurus fossils were unearthed in the Dinosaur Park Formation near Alberta, Canada, by American paleontologist Barnum Brown in the 1910s. This fossil find yielded a nearly complete skeleton, including fossilized skin remnants. Within the next two decades, more than twenty other fossils, largely skulls, were unearthed in the same formation. These were originally misidentified as alternate species, but in the 1970s, American researcher Peter Dodson reclassified the sundry fossils as one species, Corythosaurus casuarius. Some studies did continue to view Corythosaurus intermedius as another valid species, one that appeared slightly later in geological time, and research in the twenty-first century supported that view.

Many of the closest relations to Corythosaurus were likewise found in western Canada and the United States. Among these are two species of Hypacrosaurus in the Horseshoe Canyon and Oldman formations of Canada and the Upper Two Medicine Formation of Montana, at least two species of Lambeosaurus in the same Dinosaur Park Formation, and three species of Parasouralophus in the Dinosaur Park Formation and several sites in Montana, New Mexico, and Utah. All of these dinosaurs—except one species of Hypacrosaurus—were found to be contemporaries of Corythosaurus. (Hypacrosaurus altispinus lived in the final millennia of the dinosaur age.) Another closely related dinosaur, Charanosaurus jiayinensis, was discovered in the Yuliangze Formation of Heilongjiang, China, in 2000. Charanosaurus jiayinensis was a contemporary of Hypacrosaurus altispinus.

The relative abundance and high quality of Corythosaurus fossils has made them highly valuable to paleontologists. The skin impressions included on some of the earliest finds have informed studies of dinosaur physiology, and a specimen that included fossilized remains of its last meal helped researchers better understand hadrosaur diets. Corythosaurus also drew attention in 2017 with the publication of a study that matched a skull collected in 1920 by paleontologist George F. Sternberg with the rest of a skeleton excavated from the same site in 2012. This was significant as in the early twentieth century fossil hunters often focused on collecting skulls alone, and the ability to reunite complete skeletons held potential to clarify longstanding classification questions.

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