Euoplocephalus

Euoplocephalus tutus is a well-documented ankylosaurid. Researchers have discovered multiple complete skulls and at least one near-complete articulated skeleton. Its name translates to "well-armoured head," referring to its skull armour that is so extensively co-ossified it hides all cranial sutures under a layer of bone. Even the animal's eyelids were armoured with small palpebral bones that could swing into a protective position.

This moderate-sized dinosaur reached about 6 m in length and weighed roughly 2 tonnes. It followed a typical ankylosaurid body plan with an armoured back, a broad beak for cropping plants, and small, leaf-shaped teeth at the back of its jaws. Its hips were exceptionally wide and its limbs were short and stout, with the forelimbs slightly shorter than the hindlimbs. Its stiff tail ended in the famous tail club, a fused mass of vertebrae and bone. While the club on Euoplocephalus was smaller than that of Ankylosaurus, it was likely just as functional.

Shoulder and flank spikes provided additional protection, while smaller bony studs covered its back. Bony plates also protected its head, neck, and pelvis. Internally, the skull contained complex, convoluted nasal passages. These may have helped with vocalisation, moisture conservation, or regulating body temperature.

In the Dinosaur Park Formation, Euoplocephalus lived alongside various Late Cretaceous dinosaurs, including Centrosaurus, Lambeosaurus, and the predatory Gorgosaurus. It was a generalist herbivore that fed on low-lying plants like ferns, cycads, and conifers. Biomechanical analysis of the tail club (Arbour & Snively 2009) confirms it could deliver bone-breaking force. Whether these clubs were used primarily for defense against predators or for combat within the species is still a matter of scientific debate.

Some researchers, such as Bourke et al. (2018), argue that the dinosaur's complex nasal passages acted as heat-and-moisture exchangers. By condensing water from exhaled air, the animal could conserve moisture, an important adaptation for large herbivores in seasonally dry environments.

• NMC 0210 — Lambe's holotype skull, Canadian Museum of Nature.
• AMNH 5337, AMNH 5403 — multiple American Museum of Natural History specimens.
• TMP 1991.127.1 — Royal Tyrrell Museum near-complete articulated specimen.
• Multiple Dinosaur Park Formation skulls and partial skeletons across institutions.

Genus-level taxonomy — Penkalski (2018) and others have proposed splitting Euoplocephalus into multiple genera (Anodontosaurus, Scolosaurus, Dyoplosaurus) based on skull and ornament differences; current consensus is mixed, with several of these names treated by some workers as valid genera and by others as junior synonyms of Euoplocephalus tutus. Tail-club function — defence vs intraspecific combat; consensus accepts both possible. Nasal-passage function — heat-moisture recovery hypothesis (Bourke et al. 2018) is supported.

Euoplocephalus is less famous than Ankylosaurus but is the more-completely-known ankylosaurid in technical literature. It appears in many natural history museum displays, especially the Royal Tyrrell Museum and AMNH, and is a fixture of Canadian dinosaur exhibitions.

• ankylosauria
• ankylosaurus
• nodosaurus
• ornithischia

• Penkalski, P. (2018). Revised systematics of the armoured dinosaur Euoplocephalus and its allies. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, 287, 261–306.
• Arbour, V. M., & Currie, P. J. (2013). Euoplocephalus tutus and the diversity of ankylosaurid dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA. PLOS ONE, 8, e62421.
• Arbour, V. M., & Snively, E. (2009). Finite element analyses of ankylosaurid dinosaur tail club impacts. Anatomical Record, 292, 1412–1426.
• Bourke, J. M., et al. (2018). Convoluted nasal passages function as efficient heat exchangers in ankylosaurs. PLOS ONE, 13, e0207381.