Dinosaurs A to Z
Ankylosauridae

Euoplocephalus tutus YOO-oh-ploh-SEF-uh-lus

"Well-armored head"

Euoplocephalus silhouette
You 1.8 m (5.9 ft) tall
Euoplocephalus 6 m (19.7 ft) long
as long as 4 people standing fingertip to fingertip
silhouette · Andrew Farke (CC-BY) via PhyloPic
Length
6 m (19.7 ft) — About 6 m long, ~2 tonnes — slightly smaller than Ankylosaurus.
Period
Late Cretaceous (77–75 Mya)
Place
North America · Alberta, Canada
Food
Herbivore — Tough low-growing plants, probably ground level only — the head was too low to reach high vegetation.
Clade
Ankylosauridae Dinosauria Ornithischia Thyreophora Ankylosauria Club-tailed armored herbivores.

A tank-bodied plant-eater with a bony club tail and armor plates even over its eyelids.

Euoplocephalus reconstruction by Nobu Tamura (http://spinops.blogspot.com)
Reconstruction · Nobu Tamura (http://spinops.blogspot.com) (CC-BY)

Euoplocephalus was an earlier and slightly smaller ankylosaur, living about ten million years before Ankylosaurus in roughly the same part of North America. It had the same plated armor and club tail, plus an unusual extra: bony eyelids that worked like blinds, snapping shut to protect the eyes.

More about Euoplocephalus

Discovery

Named by Lawrence Morris Lambe · 1902 · the valley of the Red Deer River in present-day Dinosaur Provincial Park, Alberta, Canada

Canadian paleontologist Lawrence Morris Lambe found the first specimen on 18 August 1897. In 1902 he made it the holotype of a new species he called Stereocephalus tutus, later renamed Euoplocephalus.

Euoplocephalus means "well-armed head," from the Greek eu ("well"), hoplo~ ("armed"), and kephale ("head"). The species name tutus is Latin for "safely protected."

Lawrence Morris Lambe. A Canadian paleontologist who discovered the first specimen in Alberta and named the genus, having to rename it from Stereocephalus in 1910 after that name was found to be already in use.

Was its body armor a fixed shell or something more flexible?
The bony armor may have had a keratinThe tough protein in beaks, claws, horn sheaths, and feathers.ous covering, or it may have floated in the skin as is seen in modern crocodiles. Because the armor was heavily vascularized, it may also have played a role in thermoregulation rather than protection alone.
For the curious → What kind of plants could it actually chew?
Georg Haas (1969) studied two skulls and concluded the jaw muscles were relatively weak with movement only in the vertical plane, suggesting a diet of soft, non-abrasive vegetation. Later work argued the skull could withstand considerable force and allowed forward and sideways jaw movement, so its feeding ability is debated.

What we know

  • More than 40 skeletons known, more than any other ankylosaur.
  • Bony eyelids — unique among armored dinosaurs.
  • Tail club similar to Ankylosaurus, ending in a fused mass of bone.
  • Lived in the Dinosaur Park Formation alongside Centrosaurus, Corythosaurus, and Gorgosaurus.

What we guess

  • Whether multiple ankylosaur species in the same area filled different ecological roles.
  • Whether the tail club was used in male-male combat or only against predators.
  • Why some ankylosaurs had clubs and others (nodosaurids) had spikes instead.