Abstract
Few ankylosaurs are known from more than a single specimen,
but the ankylosaurid Euoplocephalus tutus (from the Late Cretaceous of Alberta,
Canada and Montana, USA) is represented by dozens of skulls and partial
skeletons, and is therefore an important taxon for understanding intraspecific
variation in ankylosaurs. Euoplocephalus is unusual compared to other dinosaurs
from the Late Cretaceous of Alberta because it is recognized from the Dinosaur
Park, Horseshoe Canyon, and Two Medicine formations. A comprehensive review of
material attributed to Euoplocephalus finds support for the resurrection of its
purported synonyms Anodontosaurus lambei and Scolosaurus cutleri, and the
previously resurrected Dyoplosaurus acutosquameus. Anodontosaurus is found
primarily in the Horseshoe Canyon Formation of Alberta and is characterized by
ornamentation posterior to the orbits and on the first cervical half ring, and
wide, triangular knob osteoderms. Euoplocephalus is primarily found in
Megaherbivore Assemblage Zone 1 in the Dinosaur Park Formation of Alberta and
is characterized by the absence of ornamentation posterior to the orbits and on
the first cervical half ring, and keeled medial osteoderms on the first
cervical half ring.