Scolosaurus. The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie: The results of an earlier analysis of the ankylosaurid tree by Thompson et al. (2011), is shown by this cladogram. Paleoecology Euoplocephalus, following the synonymizations proposed by Coombs (1971), was thought to exist for far longer, and was a member of more distinct faunas, than any of its contemporaries, as these fossils date to between 76.5 and 67 million years ago, in the Campanian-Maastrichtian ages of the late Cretaceous period, and came from the Dinosaur Park and Horseshoe Canyon Formations of Alberta, Two Medicine Formation of Montana, and possibly from the Oldman Formation of Alberta. Fossils that were initially believed to be from the Judith River Formation of Montana, are actually from the Dinosaur Park Formation. However, recent studies referred all Horseshoe Canyon Formation specimens to Anodontosaurus, and all Two Medicine Formation specimens to Oohkotokia. A specimen from the lowermost Dinosaur Park, or possibly from the underlying Oldman Formation, was reassigned back to Scolosaurus. Although the stratigraphic range of the holotype of Euoplocephalus is uncertain, all specimens that can be reliably referred to E. tutus came from the lower 40 m and the upper >10 m of the Dinosaur Park Formation. There are no known ankylosaurids from the top 20–25 m of the Formation. Thus, all Euoplocephalus specimens date to between 76.4 (or less) and 75.6 million years ago, in the late Campanian stage. Paleobiology According to Coombs, Euoplocephalus may have had cursorial abilities on par with those of the modern rhinoceros and hippopotamus. Based on the form of the humerus-shoulder articulation and the arrangement of the protracting muscles of the upper arm, it appears that the upper arm sloped away from the body. Coombs and Maryanska (1990) observed that Euoplocephalus specimens are usually discovered as isolated elements or partial skeletons, which suggested that this animal engaged in solitary habits and was usually either solitary or participated in small group clusters. The armor of Euoplocephalus may have had a keratinous covering, or it may have floated in the skin, as is seen in modern crocodiles. In addition to protection, the heavily vascularized armor may have had a role in thermoregulation. The palpebral bones over the eyes may have provided additional protection for the eyes. Such bones with Euoplocephalus have been discovered in the upper part of the eye socket, instead of