(Well armoured head).
Named By: Lawrence Lambe - 1910.
Synonyms: Anodontosaurus, Scolosaurus.
Classification: Chordata, Reptilia, Dinosauria, Ornithischia, Thyreophoroidea, Ankylosauria, Ankylosauridae, Ankylosaurinae.
Species: E. tutus (type).
Size: 6 meters long.
Known locations: Canada, Alberta - Dinosaur Park & Horseshoe Canyon Formation. USA, Montana - Judith River Formation.
Time period: Campanian to Maastrichtian of the Cretaceous.
Fossil representation: Multiple specimens.
is the most famous ankylosaurid dinosaur, Euoplocephalus
is one of the most important because of the huge number of remains that
have been attributed to the genus. These include remains of over
forty individual Euoplocephalus, comprising
fifteen known skulls and
some post cranial skeletons that are almost complete. This wealth of
material has not only helped to increase our understanding of
Euoplocephalus and the Ankylosauridae as a group,
but has also
revealed avenues of research that were not previously considered by
The skull is probably the single most studied area of Euoplocephalus, and is wider than it is long in form. This gives Euoplocephalus a very broad cropping mouth similar to other ankylosaurids, but different to the nodasaurids like Edmontonia and Nodosaurus which had narrow mouths. This meant that Euoplocephalus was a more generalist browser of low vegetation, and possibly had a more advanced or larger digestive system to cope with digesting a greater variety of plants. The teeth inside the mouth of Euoplocephalus are small, and like other ankylosaurids are more suitable for chopping Along with a presence of a hard palate that would allow Euoplocephalus to breathe while it had food in its mouth, it probably spent some time processing food with up and down movements of its mouth before swallowing. This processing in itself would allow ankylosaurids like Euoplocephalus to obtain more nutrition from their food regardless of if they had a more developed digestive system.
An additional area of study is the complex series of nasal passages that are in the snout. These have also been seen in other ankylosaurid genera such as Saichania, and reveal an interesting adaptation that seems to be independently evolved by the ankylosaurids, as usually it is only seen in mammals. Initial explanations for these nasal passages was that they would allow for a greater sampling of air so that Euoplocephalus could smell things, but endocasts of the brain do not support this as the olfactory region is not especially well developed to take advantage of this extra area. Instead it seems more likely that the purpose of these passages was to actually moisten air that was being breathed in. Ankylosaurids like Euoplocephalus and the aforementioned Saichania seem to have been present in ecosystems that had dry climates (either a semi-arid climate or a prolonged dry season), and that moistening the dry air as it was breathed in would make these kinds of climates far more tolerable for ankylosaurids to live in, as it would relieve them of respiratory problems as well as reduce the amount of moisture lost through respiration.
More general study of Euoplocephalus, as with other ankylosaurids, has focused upon the club like tail and body armour, the plates of which are probably the most commonly preserved fossils because of their solid form. The back and upper flanks of Euoplocephalus were covered in bony plates that are called osteoderms (also sometimes referred to as scutes). The main osteoderms were arranged in bands that followed one another down the length of the animal and formed armour that was rigid but flexible so that the normal movement of Euoplocephalus was not hindered.
In addition to the plates, large spikes rose up vertically from the body, particularly two large spikes that rose up from above the shoulders. These spikes would have made it more difficult for large predators to gain a grip on the body with their mouths, reducing the chance of effectively biting through the plates. However these spikes may have also been a form of species recognition which allowed Euoplocephalus to recognise others of their own kind from amongst similarly built ankylosaurids.
The head of Euoplocephalus was also well armoured, in fact the armour of the head was the inspiration for the name Euoplocephalus which means ‘well armoured head’. One trait that Euoplocephalus shared with other ankylosaurids was two short pyramidal horns that grew from the back of the skull, features that may have made it difficult for large theropod dinosaurs to close their mouths around the head. Euoplocephalus also possessed armoured eyelids where small bony plates could slide over the eyeball. Together with the rear head spikes this might suggest that the preferred method of attack by large predators may have been to bite at the head, an area which may have been perceived by them to be an easier target than the main body.
Like with other ankylosaurids, the lower portion of the tail of Euoplocephalus was rigid because of the support of ossified tendons in this region which meant that the only flexibility was in the upper portion of the tail. Combined with the bony club on the end, this would allow Euoplocephalus to swing its tail at other dinosaurs like it was a hammer. When this tail was used depends upon the behaviour of Euoplocephalus as while the classic image of ankylosaurids has them using their tails against predators like tyrannosaurs, they may have also used them upon each other. This means inter specific combat where two rival Euoplocephalus would face each other side to side, possibly in a head to tail orientation, and hit each other in their flanks until one submitted to the stronger individual. Combat between two Euoplocephalus is also supported by the arrangement of the armour plates located at areas such as the back of the forelimbs, areas that would have been more vulnerable to attacks from the sides rather than above.
The reasons for such combat can be very varied and range from two males competing for the right to mate with a female, territory control, or possibly even for control of a group, such as head animal in a herd, or access to a harem of a small number of females. At this time it is impossible to say which theory if any is the correct one, but even if they are correct it does not rule out the possibility of predator defence as well. After all an animal that had carried a specialised weapon that could be used against others of its own kind would have absolutely no qualms about using it against a different type of animal that was trying to kill it.
The large number of Euoplocephalus remains compared with the relatively small number of remains for other similar dinosaurs suggests that Euoplocephalus was one of the most common armoured dinosaurs in the late Cretaceous of North America. However Euoplocephalus has in the past been the subject of a lot of debate regarding its validity as a genus, as well as the remains attributed to it. First is that it may have been the same dinosaur as Ankylosaurus that was named earlier in 1908, although today this idea is no longer considered as plausible. The variation in the skulls of Euoplocephalus has also been taken to indicate either a number of individual species, or strong individual variation between different specimens of a single species (W. Coombs, 1971). As such it may be that the head spikes also served a display purpose between individuals. A number of other ankylosaurid genera have also been synonymised into the Euoplocephalus genus, although one of these, Dyoplosaurus, was resurrected as its own genus in a 2009 review of the fossil material.