Euoplocephalus (pronounced /juːˌɒplɵˈsɛfələs/ ew-OP-lo-SEF-ə-ləs) meaning 'well-armored head' (Greek eu-/ευ- meaning 'well', hoplo-/οπλο- meaning 'armed' and kephale/κεφαλη meaning 'head') was one of the largest genera of ankylosaurian dinosaurs, at about the size of a small elephant. It is also the ankylosaurian with the best fossil record, so its extensive spiked armor, low-slung body, and great club-like tail are well documented.
Size comparison between Euoplocephalus and a humanAmong the ankylosaurids, Euoplocephalus was exceeded in size only by Tarchia and Ankylosaurus. Euoplocephalus was 6 metres (20 ft) long and weighed about 2 tonnes (2.2 short tons). While it was 2.4 metres (7.9 ft) wide, it was low-slung, with short, stout legs. The rear legs were larger than the front legs and all four limbs were tipped with hoof-like claws.
Like all ankylosaurids, it had a flat, thick, triangular skull. The mouth included a horny beak and the teeth were small and roughly leaf-shaped. It had a short neck. Euoplocephalus also was a bulky, heavily armoured dinosaur with a maximum length of about 6.6 metres (22 ft) long. The armour on the top of its head and along its back and flanks were studded with large spikes, and it had a club-shaped tail. The skull had complex air passages, and an unusually solid hard palate. These may have allowed the animal to cool the air that it breathed, and to eat tough plants, suggesting that it lived in a hot, arid, environment. There is even some evidence that the animal may have possessed a salt gland next to its nostrils, which would have further aided it in a desert habitat.
Euoplocephalus tail club - Natural History Museum.The entire head and body of the Euoplocephalus are covered with bands of armor, which allowed a surprising amount of flexibility. It was the first ankylosaurid discovered with armored shutters that it could slide down to cover its eyelids.
Each piece of armor was composed 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 about 10 to 15 centimetres (3.9 to 5.9 in) long. In addition to the spines running down its back, Euoplocephalus had large horns growing from the back of its head.
It also had a bony club at the end of its rigid tail, which it carried above the ground. The tail was muscular, so the club could be swung from side to side for defense.
Internally, many bones were fused together to provide support for the heavy armor. The backbone (the dorsal vertebrae) is merged with the ribs, and several of the backbones in front of the hips (presacral vertebrae) were also fused together into a rod. The tail is made from hardened tissues, which are fused to the tail bones (known as caudal vertebrae).
RestorationEuoplocephalus as it is currently understood existed for far longer, and was a member of more distinct faunas, than any of its contemporaries (though it is possible that the fossils currently assigned to Euoplocephalus actually represent several different genera). Euoplocephalus fossils have been found in the Dinosaur Park and Horseshoe Canyon Formations of Alberta, as well as the Judith River Formation of Montana. Its fossils date to between 76.5 and 67 million years ago, in the Campanian- Maastrichtian ages of the late Cretaceous period.
Euoplocephalus was a plant eating (herbivorous) dinosaur. It had a complicated nose design (nasal structure), which indicates that it probably had a good sense of smell. It had flexible legs, which it might have used for digging. The stiff, low-slung dinosaur had poor teeth (weak dentition), so it probably would have grazed on fleshy low-lying vegetation and shallow tubers.
Euoplocephalus eating - Animatronics model in the Dino Jaws exhibition at the Natural History Museum, London.As all the skeletons discovered have been isolated, the conventional wisdom is that all ankylosaurids were solitary. However the discovery 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.
The underbelly of Euoplocephalus was not as heavily armored as its back. 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.
Partial skull of an Euoplocephalus tutus, on display at the Royal Ontario Museum, Toronto.Paleontologist Lawrence Morris Lambe discovered the first specimen (the holotype) 1902 and proposed the name Stereocephalus. However, the name was already preoccupied (the name had already been given to an insect), so he changed it to Euoplocephalus in 1910. This new name has been misspelled in more than a dozen different ways, in formal scientific literature. It was also once thought to be the same genus as Ankylosaurus.
Fossils from more than 40 individuals have been discovered in Alberta, Canada and Montana in the United States, making Euoplocephalus the best known ankylosaurid. This includes 15 skulls, teeth, and a few almost-complete skeletons, found with the armor still attached. Individual armor plates are the most commonly found element from them.
In 1971, Coombs published a landmark re-appraisal of North american ankylosaurs. He noted that among the many specimens similar to Euoplocephalus (many of which had been assigned their own genera and species), their skulls varied so much that either every known specimen must be a new species, or they all represented individual variation within a single species (E. tutus). Starting from this assumption that there was only one species of ankylosaur during the Campanian stage of the Upper Cretaceous, Coombs synonymized the genera Anodontosaurus, Dyoplosaurus, and Scolosaurus with Euoplocephalus or E. tutus, creating a species that spanned nearly ten million years, or the entire Campanian. This synonymy was followed for several decades, until scientists from the University of Alberta began to re-examine the fossils. Victoria Arbour, Michael Burns and Robin Sissons published a paper in 2009 arguing that Dyoplosaurus was in fact a valid taxon, and identified unique characteristics that differentiated it from Euoplocephalus, including its triangular claws.[2