Euoplocephalus (meaning "well armored head") was one of the main of the ankylosaurian dinosaurs at about the size of a small elephant. It is also the ankylosaurian with the best fossil evidence, so its stiff shell of spiked armor, low-slung body, and huge club-like tail are well recognized.
Among the ankylosaurids, Euoplocephalus was exceeded in dimension by only Tarchia and Ankylosaurus. Euoplocephalus was 6 meters long, and weighed about 2 metric tonnes (2.2 tons). While it was 2.4 meters (8 feet) wide, it was low-slung, with small, stout legs. The rear legs were bigger than the front legs, and all four limbs were tipped with hoof-like claws. A track way of an ankylosaur establishes in 1996 at Sucre, Bolivia indicates that Euoplocephalus might probably move fairly quickly.
Like all ankylosaurids, it has a flat, thick, triangular skull with small room left over for a brain.The mouth is a horny beak, and the teeth are small, weak and peg-like. It has a short neck.
Armed and armored
The whole head and body of the Euoplocephalus are covered with bands of armor, which allowed a surprisingly amount of flexibility. It was the first ankylosaurid exposed with armored shutters that it could slide down to cover its eyelids.
Each narrow band of armor was calm of a thick oval plate embedded in the thick surrounding skin, which was studded with short, horny spikes (dermal scutes, like those of crocodiles), which were concerning 10 to 15 centimeters (4 to 6 inches) long. In addition to the spines running down its back, Euoplocephalus had huge horns growing from the back of its head.
It also had a bony club at the ending of its rigid tail, which it approved in a raised position. The tail was muscular, so the club could be swung from side to side for protection.
Internally, many bones were fused jointly to provide support for the heavy armor. The backbone (the dorsal vertebrae) is compound with the ribs, and several of the back bones in front of the hips (presacral vertebrae) were also fused jointly into a rod. The tail is made from hardened tissues, which are compound to the tail bones (known as caudal vertebrae).
Euoplocephalus lived between 65 and 70 million years ago, in the Companion and Maastrichian ages of the late Cretaceous time.
Euoplocephalus was plant eating (herbivorous) dinosaur. It had a complex nose design (nasal structure), which indicates that it almost certainly had a good sense of smell, and flexible legs which it might have used for digging. The stiff, low-slung dinosaur had poor teeth (weak dentition), so it must have grazed on fleshy low-lying vegetation, and low tubers.
All the skeletons exposed have been isolated, so the conservative wisdom is that all ankylosaurids were solitary. However the detection of a herd of 22 young Pinacosaurus was announced in 1988, which indicates that Euoplocephalus may have displayed herd behavior, at least as a juvenile.
Only the underbelly of the Euoplocephalus was unarmored. Like a porcupine, flipping it over may have been the only way to harm it. A survey of dinosaur bones in Alberta, Canada supports this, showing many bite marks on dinosaurs like the unarmored Hadrosaurus, but none on the ankylosaurids. There is some speculation, however, that the incredible biting power of the Tyrannosaurus may have ultimately led to the species' extinction. This may have been risky because a swing of the tail could cause massive damage if it hit a marauder in the stomach, or knocked its legs out.
Classification and history
Paleontologist Lawrence Morris Lambe exposed the first specimen (the holotype) 1902, and proposed the name Stereocephalus. Unluckily, the name was already assigned to an insect (the name was preoccupied), so he changed it to Euoplocephalus in 1910. This new name has been misspelled more than a dozen dissimilar ways in formal scientific literature. It was also once consideration to be the same genera as Ankylosaurus.
The unique species is now known as Euoplocephalus tutus, and a second species, Euoplocephalus acutosquameus (originally named Dyoplosaurus), was exposed by William Arthur Parks in 1924. While the two species have clubs with different shapes, they may in fact be the same species. Specimens now assigned to the Tarchia and Ankylosaurus genera were also measured to be species of Euoplocephalus at one point.
Fossils from more than 40 individuals have been exposed in Alberta, Canada and Montana in the United States, making Euoplocephalus the most excellent known ankylosaurid. This includes 15 skulls, teeth, and one almost-complete skeleton, establish with the armor still attached. The tail club is mainly common.
The name Euoplocephalus is resulting from the Greek eu, meaning "good" or "well", hoplon meaning "weapon" or "shield", and kephale meaning "head".
A basic version of one probable evolutionary tree (a cladogram):
Ornithischia ("bird hipped" dinosaurs)
Thyreophora (the armored "shield bearers")
Ankylosauria (the tanks)
Nodosauridae (early ankylosaurians)
Polacanthinae (like Gastonia)
Shamosaurinae (like Shamosaurus)
Ankylosaurinae (like Ankylosaurus and Tarchia)