tail club knob appears circular in dorsal view, unlike that of Anodontosaurus, which appears wider than it is long or that of Dyoplosaurus, which appears longer than it is wide the presence of anteriorly-directed nares, and the absence of a continuous keel between the squamosal horn and the supraorbital bones (unlike Ankylosaurus magniventris) Paleoecology Habitat Argon-argon radiometric dating indicates that the Two Medicine Formation was deposited between 83.5 and 70.6 million years ago, during the Campanian stage of the Late Cretaceous period, in what is now northwestern Montana. If Oohkotokia is the same as Scolosaurus it would mean that Scolosaurus existed for around 3 million years. The Two Medicine Formation correlates to the Belly River Group in southwest Alberta, and the Pakowki Formation eastward. The Two Medicine Formation was deposited by rivers and deltas between the western shoreline of the Western Interior Seaway and the eastward advancing margin of the Cordilleran Overthrust Belt. Since the mid-Cretaceous, North America had been divided in half by this seaway, with much of Montana and Alberta below the surface of the water. However, the uplift of the Rocky Mountains forced the seaway to retreat eastwards and southwards. Rivers flowed down from the mountains and drained into the seaway, carrying sediment that formed the Two Medicine Formation and the Judith River Group. About 73 million years ago, the seaway began to advance westwards and northwards again, and the entire region was covered by the Bearpaw Sea, now preserved throughout the Western US and Canada by the massive Bearpaw Shale, which overlies the Two Medicine. Below this formation are the nearshore deposits of the Virgelle Sandstone. Lithologies, invertebrate faunas, and plant and pollen data support that the Two Medicine Formation was deposited in a seasonal, semi-arid climate with possible rainshadows from the Cordilleran highlands. This region experienced a long dry season and warm temperatures. The extensive red beds and caliche horizons of the upper Two Medicine are evidence of at least seasonally arid conditions. Paleofauna Scolosaurus shared its paleoenvironment with other dinosaurs, such as the duck-billed hadrosaurs Hypacrosaurus, Acristavus, Gryposaurus, Brachylophosaurus, Glishades, Prosaurolophus and Maiasaura, and the ankylosaur Edmontonia. Volcanic eruptions from the west periodically blanketed the region with ash, resulting in large-scale mortality, while simultaneously enriching the soil for future plant growth. Fluctuating sea levels also resulted in a variety of other environments at different times and places within the Judith River Group, including offshore