Euoplocephalus tutus

Euoplocephalus tutus was a large, four-legged plant eater from the Campanian coastal plain of southern Alberta. Its broad torso, short powerful limbs, reinforced skull and extensive skin armour produced the classic ankylosaur body plan. A tail club is represented among securely referred specimens, but the fragmentary holotype preserves only part of the skull roof and the first armoured neck band. For much of the twentieth century Euoplocephalus became a catch-all name for Albertan ankylosaurids spanning almost nine million years. A specimen-by-specimen revision in 2013 separated Anodontosaurus, Dyoplosaurus and Scolosaurus again, restricting E. tutus chiefly to the Dinosaur Park Formation.

Its fossils occur between approximately 76.5 and 74.9 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

Polygonal caputegulae formed a tiled surface over the low, wide skull, with small horn-like projections at its rear corners. A toothless beak cropped plants before rows of small leaf-shaped cheek teeth cut the food. Two cervical half-rings guarded the neck, and keeled osteoderms were embedded across the back and flanks, although no securely referred specimen preserves the entire armour layout in place. Toward the tail tip, tightly interlocking vertebrae and elongated tendons formed a rigid handle. Paired enlarged osteoderms created a rounded club knob capable of being swung from side to side.

• Low, broad skull covered by polygonal bony caputegulae
• Small leaf-shaped cheek teeth behind a keratinous beak
• Two segmented cervical half-rings protecting the neck
• Keeled osteoderms embedded across the back and flanks
• Short, robust limbs supporting a wide, low-slung torso
• Interlocking distal tail vertebrae forming a rigid club handle
• Rounded tail-club knob built from two enlarged major osteoderms
• Forward-facing nostrils unlike the lateral nostrils of Ankylosaurus

Lawrence M. Lambe collected holotype CMN 210 in 1897 on the east side of the Red Deer River near the mouth of Berry Creek, in what is now the northwestern part of Dinosaur Provincial Park. He named the species Stereocephalus tutus in 1902 from a fragmentary skull roof and part of the first cervical half-ring. Because Stereocephalus was already occupied by another animal, Lambe supplied the replacement genus name Euoplocephalus in 1910. Later expeditions recovered numerous skulls and partial skeletons, but modern revision showed that several of the most familiar historical specimens belong to other ankylosaur genera.

Discovery credit: Lawrence M. Lambe.

Naming authors: Lawrence M. Lambe.

Euoplocephalus lived on the warm, humid coastal plain represented by the Dinosaur Park Formation, west of the Western Interior Seaway. Meandering rivers, floodplains, ponds, swamps and forested areas supported conifers, ferns and flowering plants. The genus is most common in the formation's lower megaherbivore assemblage zone, alongside animals such as Centrosaurus, Corythosaurus, Parasaurolophus and the tyrannosaurids Gorgosaurus and Daspletosaurus.

The low muzzle and small teeth indicate selective browsing close to the ground, with swallowed vegetation probably broken down in a large fermenting gut. Biomechanical modelling shows that the largest ankylosaurid clubs could generate substantial impact forces, making defence or combat plausible. It does not reveal the target, frequency or social context of a strike. No trackway, nest or mass association securely demonstrates herd structure, parental care or other social behaviour in Euoplocephalus.

• The species was formally named in 1902, eight years before it received the genus name Euoplocephalus.
• Its holotype CMN 210 is only part of a skull roof and one armoured neck band; the familiar whole animal is a composite of referred specimens.
• A 2013 revision turned one supposed long-lived genus into at least four distinct ankylosaur genera.
• Some referred skulls preserve small bones over the eye region that could reinforce or partially cover the eyelid.
• Even after the taxonomic split, nearly the entire skeleton is represented across the securely referred material.

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1. 01
   The Paleobiology Database

   Open source
2. 02
   Estimating impact forces of tail club strikes by ankylosaurid dinosaurs

   Victoria M. Arbour · PLOS ONE · 2009

   Open source
3. 03
   Palaeobiology Collections

   Canadian Museum of Nature

   Open source
4. 04
   New genera and species from the Belly River Series (mid-Cretaceous)

   Lawrence M. Lambe · Contributions to Canadian Palaeontology · 1902

   Open source
5. 05
   Note on the parietal crest of Centrosaurus apertus and a proposed new generic name for Stereocephalus tutus

   Lawrence M. Lambe · The Ottawa Naturalist · 1910

   Open source
6. 06
   Euoplocephalus tutus and the diversity of ankylosaurid dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA

   Victoria M. Arbour, Philip J. Currie · PLOS ONE · 2013

   Open source
7. 07
   Museum Experience 2023–2024

   Royal Tyrrell Museum of Palaeontology · 2023

   Open source
8. 08
   Dinosaur Provincial Park

   UNESCO World Heritage Centre

   Open source