April 4, 2022 Scott Kraus

Edmontosaurus is a Cretaceous Hadrosaur 

Edmontosaurus, pronounced “ed-MON-toh-Sawr-us” was a crestless hadrosaurid, or duck-billed, herbivorous dinosaur. It consists of two species, Edmontosaurus regalis and Edmontosaurus annectens. It lived over a wide area in western North America during the Cretaceous Period. The fossils of the first species, E. Regalis, were identified as living 73 million years ago, about 8 million years after the second species was dated.

Quick Facts

What did Edmontosaurus look like?

Edmontosaurus was a large, four-legged, scaled, herbivorous dinosaur.  The Edmontosaurus would eat plants and grasses, and chew up its meal in its uniquely shaped jaw, while trying not to become a meal itself.

Its mouth closely resembled a duck’s bill and the flattened and prominent nose is a defining characteristic of the species.  Their elongated skulls were supported by a hefty spinal column and massive rear legs.

The front legs did not have the girth of the back legs, and were not as long either.

Despite the front legs being used for locomotion at slow speeds, the Edmontosaurus most likely propelled itself to a reasonably fast gait using only its rear legs.  The Edmontosaurus had a tail, positioned high on the hips, and held rigidly extended due to ossified tendons to help balance the dinosaur when running on two legs.

At a height of over two and a half meters at the hip, the Edmontosaurus was estimated to weigh over four and a half tons.

Its shear size would have kept it safe from all but the biggest and most powerful of theropods (T-Rex and the like).  This made it one of the dominant herbivores of the era, second to Triceratops.

What are the physical characteristics of the Edmontosaurus?

As a member of the Hadroauridae family, Edmontosaurus’ shared the name sake “duck bill” common in this family of dinosaurs.  The flattened nose jaw helped direct food to its grinding surfaces between top and bottom teeth, and to store chewed food in its cheek pouches.

Teeth however, were only placed along the sides of the mouth, in the middle a hardened non-bony beak would have been present.  This beak could be quite large, sometimes extending as much as eight inches past the bones of the skull.  Teeth were constantly discarded and replaced due to wear, from a row of already developed teeth suspended above the teeth, with new teeth taking only six months to form.

To support the massive weight of the Edmontosaurus there were several adaptions to its hip and tail bones.  The nine vertebrae directly above the hip joint were fused together, forming a strong bony structure with which to distribute the giant creature’s weight.

The tail was also altered to improve its posture as such a large animal.  The tendons between vertebrae were ossified or hardened, to limit range of motion and increase rigidity along the tail.  The combination of these two factors would have limited the Edmontosaurus’ ability to stand completely erect on its hind legs, making it possible only with support or while running.

As an odd feature, it also had more fingers than toes, with four fingers per forearm and only three toes per foot.  Also, each toe was covered in a soft, abrasive resistant pad, similar to a camel’s hoof.

What did Edmontosaurus Eat?

Edmontosaurus was a terrestrial herbivore, which means it ate plants from the ground. It used its broad beak to grab foliage and it had hundreds of teeth in rows that were not always in use. The teeth were deeply indented in the jaw which leads paleontologists to believe that they had cheek structures or “pouches” to keep food in the mouth. There is evidence of stomach contents containing fossilized plant matter, but paleontologists are not decided about whether it was eaten by the dinosaur, or washed into the “stomach'” after it died.

How did Edmontosaurus Move?

Edmontosaurus is believed to have been a facultative biped, which means that it could move from movement on four legs to a bipedal stance when sitting or moving slowly. This was a common trait among hadrosaurids. In 2007, research was done with computer modeling on the movement of Edmontosaurus and it suggested that the hadrosaur could run very fast, up to 28 mph, albeit quadrupedally. It was once thought that hadrosaurids was at least partially aquatic, but an inspection of their slim hands suggests that they were not equipped for propulsion underwater, their tail was not suited for propulsion either.

Edmontosaurus could have been Migratory

Paleontologists look at the wide distribution of Edmontosaurus, combined with the fact that some of its territory had little sunlight during a substantial part of the year, and believe it is very possible that it was migratory. A 2008 report of dinosaur migration asserted that it could make 1,600 miles (2,600 km) round-trip if it had the right metabolism, fat deposition rates, and it could make the required speeds per hour, 1-6 mph (2-10 kmh). However, other scientists believe that Edmontosaurus “overwintered”, or waited through the low-light season.

Edmontosaurus was a Social Dinosaur

Edmontosaurus fossils have been found in bone beds, or groups of many skeletons in the same area, in Alaska, Alberta, South Dakota, and Wyoming. This is a strong indicator that the dinosaur was social and formed herds. In Wyoming, a really high concentration of this dinosaur was found. Paleontologists found the remains of an estimated 10,000 to 25,000 Edmontosaurus in a little over a square kilometer, although most were in only .15 miles of that area.

Predators of Edmontosaurus

The fossil evidence shows that Edmontosaurus was a favorite snack for theropods. A skeleton on display at the Denver Museum of Nature and Science shows evidence of a theropod bite in the tail and other damage to the spines from an attack that came from the rear. Luckily for this particular Edmontosaurus, it was able to escape it’s attacker. Paleontologists believe it may have outmaneuvered the predator or used it’s tail as defense. The wounds had time to partially heal before the dinosaur died. Most were not so lucky, tooth marks have been found at several bone beds and another skeleton found in South Dakota escaped some small attacking theropod, only to succumb to the injuries shortly thereafter.

Where did Edmontosaurus Live?

Edmontosaurus was a very common dinosaur during the last interval before the Cretaceous-Paleogene extinction event, which caused the extinction of non-avian dinosaurs. It has been reported to have made up one-seventh of the sample of dinosaurs that we know lived during the time. Edmontosaurus lived on the coastal plain extending from Colorado to Saskatchewan. Triceratops was the only dinosaur that was more prevalent in the area during this time period. The area is thought to have been flat, with forests and a subtropical climate with many varieties of plants, like conifers, palmettos and ferns, and animals like turtles, monitor lizards, and tree-dwelling mammals.

The Discovery of Edmontosaurus

Edmontosaurus was first described by Lawrence Lambe in 1917, although in the 19th century many fossils of the species had been found and attributed to different species. Two partial skeletons were found, one in 1912 and one in 1916, in what used to be called the Edmonton Formation of Alberta Canada. The name of the formation was how the dinosaur got its name. Thanks to Lambe’s new classification of Edmontosaurus, that led to other previously misnamed fossils finally getting their recognition as belonging to the new species. Edmontosaurus fossils have been found in several states in the western United States and as far south as Texas.

The Importance of Edmontosaurus

Edmontosaurus was important because it was one of the last non-avian dinosaurs before the great extinction at the end of the late Cretaceous. It was also very widely distributed across the western North America, so paleontologists have the advantage of many fossils in many conditions to study, including near-perfect fossils. In 1994, the author Kraig Derstler even described Edmontosaurus annectens as “perhaps the most perfectly-known dinosaur to date”. Paleontologists should be so lucky with other species! However, it is still great for paleontology when even one species is so well-represented in the fossil records. We can learn a lot about dinosaurs in general from these records and the exotic time period that Edmontosaurus lived in so long ago.