About Edmontonia
| Scientific Name (Genus) | Edmontonia |
| Meaning of Name |
Of Edmonton (a place in Canada)
Edmonton (Edmonton Formation) [place name] -ia [Latin suffix] |
| Classification | Ornithischia, Thyreophora (Thyreophoroidea, Ankylosauria, Nodosauridae, Nodosaurinae, Panoplosaurini) |
| Total Length | Approx. 6.0 - 6.6m (Shoulder height approx. 2.0m, Weight approx. 3.0 - 4.0 tons) |
| Diet | Herbivorous |
| Period | Late Cretaceous (approx. 83.5 - 66 million years ago) |
| Sub-classification / Species Name |
Edmontonia longiceps
Edmontonia rugosidens |
| Year of Paper Publication | 1928 |
| Genus Name Publication |
A new armored dinosaur from the Edmonton Formation of Alberta.
Transactions of the Royal Society of Canada, series 3. 22. by Sternberg, C.M. 1928. |
Characteristics: The Heavy Armor and Giant Spikes of a "Walking Tank"
Edmontonia was an herbivorous dinosaur characterized by its massive body exceeding 6 meters in length and the hard bony plates (armor) covering its back, sides, and even its neck. This extreme defensive style truly made it worthy of being called a "walking tank."
It is believed to have evolved such heavy armor to defend against giant tyrannosaurid carnivores like Gorgosaurus and Albertosaurus that lived during the same period.
Edmontonia is classified in the "Nodosauridae" family of armored dinosaurs. Unlike the Ankylosauridae, it did not have a bony club at the end of its tail. Instead, a major feature was the development of very large spikes projecting forward and downward from its shoulders.
When defending against carnivorous dinosaurs, it is thought to have crouched down to hide its vulnerable soft underbelly against the ground, presenting its back armor and giant shoulder spikes to outlast the enemy. It has also been suggested that these shoulder spikes might have been used in contests of strength (locking horns) between males fighting over territory or mates.
In the past, heavily armored dinosaurs were thought to have a sprawling, lizard-like crawling posture. However, recent research indicates that Edmontonia's limbs were positioned more upright to stably support its heavy body while walking.
Amazing Physical Functions: Complex Noses and Excellent Chewing Ability
Edmontonia was not just a dinosaur with defensive power; it had sophisticated physical functions. Recent research using CT scans has revealed that its nasal airway had a complex structure, looping back and forth.
Operating a massive body weighing several tons generates an enormous amount of heat. It is thought that the extensive and complex mucous membranes in its nasal cavity acted like a heat and moisture exchanger during breathing, helping to regulate body temperature and protect the brain from heat.
It also possessed excellent eating abilities. Previously, because the teeth of armored dinosaurs were small and simple, they were thought to have poor chewing ability and swallowed plants whole. However, detailed analysis of microscopic tooth wear revealed that Edmontonia performed a complex "front-to-back chewing motion," pulling its lower jaw back as it closed its mouth.
By accurately occluding its blade-like upper and lower teeth, it could efficiently grind plant fibers, suggesting it engaged in "selective foraging" by choosing to eat highly nutritious plants.
History of Discovery and Classification
Edmontonia fossils were discovered in 1915 in Alberta, Canada, by Barnum Brown, a paleontologist from the American Museum of Natural History. This was an articulated, nearly complete front half of the body.
However, it was not given a formal new genus name at the time and was temporarily classified with a dinosaur called "Palaeoscincus."
Palaeoscincus means "ancient skink (lizard)" and is a dinosaur named in 1856 based solely on a single fossilized tooth. Since a single tooth cannot accurately define a species, it was used in early dinosaur research as a "wastebasket" taxon to temporarily toss in unidentified armored dinosaur fossils. It is currently considered a nomen dubium (doubtful name).
A turning point came in 1924. An expedition led by Charles Sternberg of the Geological Survey of Canada discovered a wonderfully preserved fossil, including a complete skull. Based on this specimen, a new genus was described in 1928 as "Edmontonia longiceps." The name is derived from the Edmonton Formation, where it was discovered.
Subsequently, fierce debates continued for many years over whether Edmontonia was the same kind of dinosaur as others like Panoplosaurus or Denversaurus. However, due to differences in the smoothness of the armor surface and skull features, it is now recognized as an independent dinosaur.
The Two Species of Edmontonia
The genus Edmontonia currently has two mainly recognized species: "longiceps" and "rugosidens." They lived in slightly different eras, and it is thought their appearances changed during the evolutionary process.
| Feature | E. longiceps | E. rugosidens |
|---|---|---|
| Period of existence | Approx. 72 million years ago (slightly newer) | Approx. 76.5 - 74.4 million years ago (slightly older) |
| Snout shape | Elongated and narrow | Short, broad, and plump |
| Shoulder spikes | Single and relatively short | Giant with bifurcated (split) tips |
| Head armor | No projecting processes behind the eyes | Lateral projecting processes behind the eyes |
Paleoecology and the Mystery of Fossilization (Coastal Plain Flooding Hypothesis)
Western North America, where Edmontonia lived, was covered by a shallow sea at the time and had a warm, humid monsoon climate. It seems the giant herbivorous dinosaurs did not make long migrations but settled in specific plains rich in ferns and conifers.
Many Edmontonia fossils are found lying face down, with their back armor plates and spikes in the positions they held in life. The environment of that time is deeply related to this.
It is thought that when severe rainstorms or storm surges occurred during the rainy season and the plains suddenly submerged, the heavy and slow-footed Edmontonia failed to escape and drowned. The carcasses drifted on the water surface and washed up in large numbers in wetlands after the water receded. They were then rapidly buried by sediment, allowing them to remain as beautiful fossils without flipping onto their backs.
Edmontonia Stamp and Fossil Gallery
