About Stegoceras
| Scientific Name (Genus) | Stegoceras |
| Meaning of Name |
Horned roof
stegos (roof) [Greek] - keras (horn) [Greek] |
| Classification | Ornithischia, Pachycephalosauria (Pachycephalosauridae) |
| Total Length | Approx. 2-2.5m |
| Diet | Herbivorous (or omnivorous) |
| Period | Late Cretaceous (Campanian to Maastrichtian, approx. 78 to 74 million years ago) |
| Sub-classification / Species Name | Stegoceras validum |
| Year of Paper Publication | 1902 |
| Genus Name Publication |
New genera and species from the Belly River Series (mid-Cretaceous).
Geological Survey of Canada, Contributions to Canadian Palaeontology. 3. by Lawrence Lambe. 1902. |
Features: A Dinosaur for Understanding Pachycephalosaurs
Stegoceras was a small to medium-sized herbivorous dinosaur that lived on the North American continent during the Late Cretaceous period of the Mesozoic era. It belonged to the Pachycephalosauria (Pachycephalosauridae family) and had a build similar to that of a modern goat.
While mostly only the skulls of pachycephalosaurs have been found, Stegoceras is a dinosaur for which nearly complete fossils of the postcranial skeleton (the skeleton below the neck) have been discovered. Therefore, it is highly valued in paleontology as a "model dinosaur" for understanding the body structure and evolution of pachycephalosaurs as a whole.
A Dome for Head-Butting
The most prominent feature of Stegoceras is its extremely thick, dome-shaped domed top of the head.
Recent studies have revealed that this dome has traces of post-traumatic osteomyelitis (bone lesions caused by strong impacts) concentrated near the "apex" of the top of the head. This is considered evidence that they engaged in "head-butting" behavior, clashing heads head-on during territorial disputes with peers or fights over mates.
A Full-Body Structure to Withstand Head-Butting and the "Tail Basket"
Because it engaged in the violent behavior of head-butting, Stegoceras's entire body had undergone special evolution to withstand the impact. It possessed an unusually wide and robust pelvis, along with well-developed hind leg muscles. These were structures to withstand the repulsive force of head-butting and to stand firm.
Additionally, small bone fragments previously found near the abdomen of Stegoceras were thought to be "gastralia" (belly ribs that support the abdomen), which are rare for ornithischian dinosaurs. However, subsequent detailed research revealed that these were not gastralia, but rather special bones arranged to surround the tail.
Tail Basket (Ossified Tendons)
In the tail of Stegoceras, bones called "ossified tendons," where the boundaries of muscles had turned into bone, were arranged in multiple parallel layers, creating a structure that enveloped the entire circumference of the tail. This is also called a "tail basket," and it is thought to have functioned to prevent the spine from bending like a whip and getting damaged by the impact of head-butting.
The Brain Structure and Excellent Sense of Smell of Stegoceras
As a result of examining the inside of its thick skull with a CT scan, interesting facts about the shape and function of Stegoceras's brain have also been discovered.
Although the overall size of its brain was small, the part that detects smells, the "olfactory bulb," was very well developed. Its keen sense of smell was comparable to that of the contemporary Triceratops, and it is thought that it lived relying on its sense of smell as much as or more than its eyesight.
Deep inside the nose, there was a complex bone structure that efficiently flowed air. It is speculated that this not only helped detect smells but also acted as a cooling device like a "radiator" to prevent the brain from becoming too hot due to the intense exercise of head-butting.
Changes in Appearance with Growth
Just as the juvenile of Pachycephalosaurus is thought to have been "Dracorex," Stegoceras also experienced dramatic changes in appearance as it grew.
In the past, small fossils with flat tops of the head were found and thought to be a different kind of dinosaur called Ornatotholus. However, subsequent detailed research revealed that this Ornatotholus was not an independent dinosaur, but rather a juvenile (child) of Stegoceras whose dome had not yet developed.
It is known that as Stegoceras grew, its flat head rapidly rose into a thick dome shape. The fact that the dome on the head developed rapidly before the body grew to its maximum size suggests that they had a complex sociality and placed importance on appealing to peers and fighting.
Discovery and Paper Publication
Between 1898 and 1903, three partial skull fossils were collected in Alberta by Canadian paleontologist Lawrence Lambe.
Source: New genera and species from the Belly River Series (mid-Cretaceous). Geological Survey of Canada, Contributions to Canadian Palaeontology. 3. by Lawrence Lambe. 1902.
In 1902, based on these, Lambe published a paper describing a new genus and species, Stegoceras (Stegoceras validum). At the time, the true nature of the dome on its head was unknown, and it was thought to be the core of a horn of a ceratopsian like Triceratops, or a part of a thyreophoran like Stegosaurus. Because body fossils had not been found, they were unable to determine its overall appearance or classification.
Later, in 1924, American paleontologist Charles Gilmore described a well-preserved specimen with a complete skull connected to a body, confirming that Stegoceras was a bipedal dinosaur with a unique dome. Along the way, there was a time when it was mistakenly thought to be in the same group as the carnivorous dinosaur Troodon because of their similar tooth shapes, but they were clearly distinguished in 1945, and it is now known as an important dinosaur representing the pachycephalosaurs.